Get 20M+ Full-Text Papers For Less Than $1.50/day. Start a 14-Day Trial for You or Your Team.

Learn More →

Fine Exploration and Control of Subway Crossing Karst Area

Fine Exploration and Control of Subway Crossing Karst Area applied sciences Article Fine Exploration and Control of Subway Crossing Karst Area Jing Wang , Liping Li *, Shaoshuai Shi * , Shangqu Sun, Xingzhi Ba and Yijie Zhang School of Qilu Transportation, Shandong University, Jinan 250061, China * Correspondence: liliping@sdu.edu.cn (L.L.); shishaoshuai@sdu.edu.cn (S.S.) Received: 13 May 2019; Accepted: 22 June 2019; Published: 26 June 2019 Featured Application: Accurate exploration and safety control of karst caves in subway construction. Abstract: A large number of subway projects need to cross all kinds of disaster sources during the construction process. When a disaster source is unknown and uncertain, it is dicult for tunnel stability analysis to conform to the actual situation, which is likely to cause serious geological disasters. Firstly, the accurate location of the source of the disaster is realized via the geophysical method, and the orientation of the target is determined. Secondly, real imaging of the geological disaster source is realized using fine three-dimensional scanning equipment. Finally, the coupling law of the seepage field, displacement field, and stress field of the tunnel surrounding rock are analyzed. The stability of the tunnel is analyzed, and the reasonable karst treatment method is put forward. Keywords: disaster source; geophysical method; orientation of the target; reasonable karst treatment method 1. Introduction The distribution area of karst in China is 3.65 million square kilometers, accounting for more than one-third of the territory. Karst is most developed in the Southern provinces of Guizhou, Hunan, Jiangxi, Sichuan, Yunnan, and Hubei, and in the Northern provinces of Hebei, Shandong, and Liaoning. Additionally, many karst development areas are distributed in metro construction cities, such as Jinan Metro, which needs to pass through hard rock water-rich caves [1], Wuhan Metro, which needs to pass through “honeycomb caves”, Changsha Metro, which needs to pass through complex underwater caves, and so on. In the soluble strata, limestone may contain limestone fragments and fissures locally (Figure 1). The existence of limestone fissures provides water storage conditions and transportation channels for groundwater [2]. Caves of di erent sizes, shapes, and buried depths are formed due to the dissolution and erosion of groundwater [3]. If these caves are not accurately identified, the following risks are likely to occur: 1. Shield machine pitch, jamming or water inrush (Figure 2); 2. Karst cave collapse above the tunnel leading to the surface collapse; 3. During the operation period, vehicle vibration causing surface collapse or karst cave collapse under the segment, which leads to risks in train operation; 4. The existence of karst water leading to the continuous development of karst caves, which threatens the long-term operation of the metro. Appl. Sci. 2019, 9, 2588; doi:10.3390/app9132588 www.mdpi.com/journal/applsci Appl. Sci. 2019, 9, x 2 of 17 Appl. Sci. 2019, 9, 2588 2 of 17 Appl. Sci. 2019, 9, x 2 of 17 (a) (b) Figure 1. Dissolution limestone and limestone fragments. (a) dissolution limestone; (b) limestone (a) (b) fragments. Figure Figure 1. 1. D Dis isso so lulu tition lim on limeste osnto ene and l and limesitm oneesto frange frag mentsm . (e ants. ) diss(o al) di utiosso n lilu mtion lim estone; (best ) lio m ne; ( estob ne ) lim fragest meo nne ts. fragments. (a) (b) Figure 2. Figure 2. Wate Water r inru inrush sh from from s shield hield tunnel. tunnel. ( (a a) front of the ) front of the tunnel; ( tunnel; (b b) ) inside inside the tunnel. the tunnel. (a) (b) In the aspect of karst detection, a large number of geophysical methods (including electrical, In the aspect of karst detection, a large number of geophysical methods (including electrical, Figure 2. Water inrush from shield tunnel. (a) front of the tunnel; (b) inside the tunnel. electromagnetic, elastic wave, and microgravity) have emerged [4–13]. However, the geological electromagnetic, elastic wave, and microgravity) have emerged [4–13]. However, the geological conditions In the a insthe pect of karst ka ar rst detecti ea are complex, on, a la and rge number it is di of geophysic cult to accurately al minvestigate ethods (incthe luding electric underground al, conditions in the karst area are complex, and it is difficult to accurately investigate the underground conditions by a single geophysical method [14,15]. With the advancement of geophysical methods and electromagnetic, elastic wave, and microgravity) have emerged [4–13]. However, the geological conditions by a single geophysical method [14,15]. With the advancement of geophysical methods interpr conditions etation in ttechniques, he karst are gr a eat are achievements complex, and it have is di been fficmade ult to in acc karst urate exploration ly investigat [16 e t ].hMor e underg e successful round and interpretation techniques, great achievements have been made in karst exploration [16]. More detection cases demonstrate that comprehensive detection method can e ectively reduce the uncertainty conditions by a single geophysical method [14,15]. With the advancement of geophysical methods successful detection cases demonstrate that comprehensive detection method can effectively reduce and and interpret reduce the ation error techniques, g interpretation reat results achievements when exploring have been the under made in karst explora ground karst structur tion [16 e. Ho ]. Mor wever e, the uncertainty and reduce the error interpretation results when exploring the underground karst geophysical prospecting methods can only locate karst caves, which is dicult to quantify. Borehole successful detection cases demonstrate that comprehensive detection method can effectively reduce structure. However, geophysical prospecting methods can only locate karst caves, which is difficult laser the uncertain scanningty and red technology ucis e the error in a method toterpretati get the point on recloud sults when data of exploring the three-dimensional the undergroun surface d karof st to quantify. Borehole laser scanning technology is a method to get the point cloud data of the three- the inner wall of the cavity by extending the probe with integrated laser scanning function into the structure. However, geophysical prospecting methods can only locate karst caves, which is difficult dimensional surface of the inner wall of the cavity by extending the probe with integrated laser cavity to qua.nIts tify. Borehol principle is e la the ser sca same nni asng that technol of theostanding gy is a method to get the poi laser scanner, but its ng t cl reatest oud da advantage ta of the three- is the scanning function into the cavity. Its principle is the same as that of the standing laser scanner, but miniaturization of the laser probe, which can adapt to various narrow channels and space and get data dimensional surface of the inner wall of the cavity by extending the probe with integrated laser its greatest advantage is the miniaturization of the laser probe, which can adapt to various narrow deep scanni into ng functi the rock on i mass nto the ca [17,18vi ]. ty. Its pri At present, ncidrilling ple is the laser same technology as that of is the sta mainly nding l used in aser sca the goaf nner, but of coal channels and space and get data deep into the rock mass [17,18]. At present, drilling laser technology mine, but it is not combined with geophysical prospecting methods, which leads to the problem of its greatest advantage is the miniaturization of the laser probe, which can adapt to various narrow is mainly used in the goaf of coal mine, but it is not combined with geophysical prospecting methods, blind channel drilling. s and sp Ther ace efor and get e, this dat paper a deep synthetically into the rock determines mass [17,18the ]. At karst present development , drilling laar ser ea teby chn means ology which leads to the problem of blind drilling. Therefore, this paper synthetically determines the karst of various geophysical prospecting. Targeted drilling and quantitative exploration of karst cave by is mainly used in the goaf of coal mine, but it is not combined with geophysical prospecting methods, development area by means of various geophysical prospecting. Targeted drilling and quantitative drilling which lelaser ads to ar tehcarried e proble out. m of blind drilling. Therefore, this paper synthetically determines the karst exploration of karst cave by drilling laser are carried out. development area by means of various geophysical prospecting. Targeted drilling and quantitative 2 explorat . Quanti ionta oti f k ve a rstEx cplorati ave byo drn Met illing lh aod ser arof Ka e carrirst ed out Cave Ba . sed on Three-Dimensional Laser Measurement 2. Quantitative Exploration Method of Karst Cave Based on Three-Dimensional Laser Measurement Appl. Sci. 2019, 9, 2588 3 of 17 Appl. Sci. 2019, 9, x 3 of 17 2. Quantitative Exploration Method of Karst Cave Based on Three-Dimensional Laser Measurement 2.1. 3-D Automatic Laser Scanning Technology 2.1. 3-D Automatic Laser Scanning Technology Three-dimensional automatic laser scanning technology uses laser diodes to emit laser pulses. Three-dimensional automatic laser scanning technology uses laser diodes to emit laser pulses. Laser pulses propagate to the target point under testing [19]. The photosensitive secondary tube Laser pulses propagate to the target point under testing [19]. The photosensitive secondary tube receives laser signals reflected from the surface of the object. The “flight time” of the laser is receives laser signals reflected from the surface of the object. The “flight time” of the laser is calculated. calculated. The distance L between the scanner and the target point under testing is calculated by the The distance L between the scanner and the target point under testing is calculated by the speed of speed of light C and the “flight time” Δt. A precision clock control encoder synchronously measures light C and the “flight time” Dt. A precision clock control encoder synchronously measures transverse transverse scanning angle observation value alpha and longitudinal scanning angle observation scanning angle observation value alpha and longitudinal scanning angle observation value beta of value beta of each laser pulse. Laser scanning three-dimensional measurement uses the internal each laser pulse. Laser scanning three-dimensional measurement uses the internal coordinate system coordinate system of the instrument. The X-axis is in the transverse scanning plane, the Y-axis is of the instrument. The X-axis is in the transverse scanning plane, the Y-axis is perpendicular to the perpendicular to the X-axis in the transverse scanning plane, and the Z-axis is perpendicular to the X-axis in the transverse scanning plane, and the Z-axis is perpendicular to the transverse scanning transverse scanning plane (Figure 3). The formula for calculating the coordinates of three- plane (Figure 3). The formula for calculating the coordinates of three-dimensional laser foot points can dimensional laser foot points can be obtained as follows: be obtained as follows: L = cDt (1) (1) 𝐿 𝑐∆𝑡 8 9 8 > x > > L cos cos > > > > > > 𝐿cos𝛽cos𝛼 < = < y = L cos sin (2) > > > > >𝑦 > 𝐿cos𝛽sin𝛼 (2) > > > : ; : z L sin 𝐿sin𝛽 In the formula, C is the propagation speed of the laser in the atmosphere, Dt is the round-trip In the formula, 𝐶 is the propagation speed of the laser in the atmosphere, ∆𝑡 is the round-trip propagation time of the laser at the distance to be measured, is the observation value of the transverse propagation time of the laser at the distance to be measured, 𝛼 is the observation value of the scanning angle, and is the observation value of the longitudinal scanning angle. transverse scanning angle, and 𝛽 is the observation value of the longitudinal scanning angle. (a) (b) Figure 3. Schema of propagation time ranging method and internal coordinate system of laser Figure 3. Schema of propagation time ranging method and internal coordinate system of laser detector. ( detector a) schema . (aof ) schema of propagation time ranging method; propagation time ranging method; (b) the internal (b) the coor internal dinatecoordinate system of syst laser em of detector laser . detector. The automatic laser scanning system of the empty area is mainly divided into horizontal scanning mode and vertical scanning mode. The automatic laser scanning system of the empty area is mainly divided into horizontal scanning mode and vertical scanning mode. Horizontal scanning mode: The most commonly used scanning mode. First, the scanning head • Horizontal scanning mode: The most commonly used scanning mode. First, the scanning head rotates vertically to the position of vertical angle 0 (the upper part of the detector is straight) rotates vertically to the position of vertical angle 0° (the upper part of the detector is straight) and begins the first round of complete 360 horizontal scanning. After each circle of horizontal and begins the first round of complete 360° horizontal scanning. After each circle of horizontal scanning, the scanning head increases the increment of steps set by the user along the vertical scanning, the scanning head increases the increment of steps set by the user along the vertical direction and starts the next circle of horizontal scanning until the vertical axis rotates 180 in direction and starts the next circle of horizontal scanning until the vertical axis rotates 180° in the vertical direction. During the last horizontal scan of the scanner head, the laser emission and the vertical direction. During the last horizontal scan of the scanner head, the laser emission and receiving lens of the scanner head point in front of the detector (Figure 4). receiving lens of the scanner head point in front of the detector (Figure 4). Vertical scanning mode: Vertical scanning is suitable for scanning under some special conditions. • Vertical scanning mode: Vertical scanning is suitable for scanning under some special Especially, the scanning line obtained is perpendicular to the horizontal characteristics of the conditions. Especially, the scanning line obtained is perpendicular to the horizontal scanning object so that more details that are comprehensive can be captured. As shown in the characteristics of the scanning object so that more details that are comprehensive can be figure, in the vertical scanning process, the scanning head first rotates from vertical angle position captured. As shown in the figure, in the vertical scanning process, the scanning head first rotates 0 (the vertical direction behind the detector) to vertical angle position 180 (the laser-transmitting from vertical angle position 0 (the vertical direction behind the detector) to vertical angle and -receiving lens of the scanning head points in front of the detector) along the vertical direction position 180° (the laser-transmitting and -receiving lens of the scanning head points in front of the detector) along the vertical direction and completes the first vertical scanning. After each vertical scan, the scanning head increases a user-set increment along the horizontal direction Appl. Sci. 2019, 9, 2588 4 of 17 Appl. Appl. Sci. Sci. 2019 2019, , 9 9, x , x 4 of 4 of 17 17 and completes the first vertical scanning. After each vertical scan, the scanning head increases a user-set increment along the horizontal direction and starts the next vertical scan until the and starts the next vertical scan until the horizontal axis rotates 360 degrees in the horizontal and starts the next vertical scan until the horizontal axis rotates 360 degrees in the horizontal horizontal axis rotates 360 degrees in the horizontal direction (Figure 5). direct direction ion (F (Fig igure ure 5) 5).. Figure 4. Figure 4. Horizontal scanning mode. Horizontal scanning mode. Figure 4. Horizontal scanning mode. Figure 5. Vertical scanning mode. Figure 5. Vertical scanning mode. Figure 5. Vertical scanning mode. 2.2. Data Processing of Laser Point Cloud 2.2. Data Processing of Laser Point Cloud 2.2. Data Processing of Laser Point Cloud Aft Afte er r obt obta ain ini in ng t g th he o e or rig igin ina al l point point clo clou ud d dat data a vi via a a lase a laser three-dimen r three-dimens sion iona al measur l measurement sy ement system, stem, After obtaining the original point cloud data via a laser three-dimensional measurement system, it is necessary to filter, stitch, and model the original point cloud data. Specifically, as follows: it is necessary to filter, stitch, and model the original point cloud data. Specifically, as follows: it is necessary to filter, stitch, and model the original point cloud data. Specifically, as follows: Data Data filterin filtering g:: Due to the Due to the influence o influence of f e ex xternal ternal envir enviro onmental nmental factors factors and the and the uneven re uneven reflection flection Data filtering: Due to the influence of external environmental factors and the uneven reflection characteristics of the empty area wall during the scanning process, the final scanned point cloud data characteristics of the empty area wall during the scanning process, the final scanned point cloud data characteristics of the empty area wall during the scanning process, the final scanned point cloud contain no contain no distance po distance points and bad points. At th ints and bad points. At the same e same time, time, the rapid the rapid oper operation ation of a laser of a laser range range data contain no distance points and bad points. At the same time, the rapid operation of a laser finder during scanning will also lead to the phenomenon of an “intermediate medium point” in finder during scanning will also lead to the phenomenon of an “intermediate medium point” in range finder during scanning will also lead to the phenomenon of an “intermediate medium point” in dif diff ferent erent pha phas ses of t es of th he e la lase ser beam, re r beam, resu sult lting in po ing in point int displ displa acement cement. . For t For th his re is reaso ason n, point , point clou cloud dat d data a di erent phases of the laser beam, resulting in point displacement. For this reason, point cloud data are processed by filtering out single obvious bad points in scanning. are processed by filtering out single obvious bad points in scanning. are processed by filtering out single obvious bad points in scanning. Fi Firstly, rstly, a accordi ccordin ng to the fixed spa g to the fixed spac ce e ra range of nge of th the worki e workin ng g a ar rea ea, the poi , the poin nt beyond thi t beyond this s ra range ca nge can n Firstly, according to the fixed space range of the working area, the point beyond this range can be be considered as noise point filtering. Secondly, on the same scanning plane, if the distance between be considered as noise point filtering. Secondly, on the same scanning plane, if the distance between considered as noise point filtering. Secondly, on the same scanning plane, if the distance between a a point a point and and it its adj s adja acent cent t tw wo point o points s exce exceeds a ce eds a cert rtain t ain tr rust uste ed va d valu lue, e, t th he point e point is consider is considered di ed dis st tort ortiion on point and its adjacent two points exceeds a certain trusted value, the point is considered distortion point filtering. However, considering the point of edge, because it is far from the scanning center, the point filtering. However, considering the point of edge, because it is far from the scanning center, the point filtering. However, considering the point of edge, because it is far from the scanning center, d diis st tan anc ce e b be et tw we ee en n s sa am mp plliin ng g p po oiin nt ts s i is s v ve er ry y lla ar rg ge e.. At At this ti this time, the a me, the an ngl gle between t e between th he combi e combin niin ng poi g poin nt t the distance between sampling points is very large. At this time, the angle between the combining and the front and back points on the scanning line is considered as a distortion point if the angle and the front and back points on the scanning line is considered as a distortion point if the angle point and the front and back points on the scanning line is considered as a distortion point if the angle bet betw ween t een th hem is em is les less s t th han an a c a ce ert rta aiin con n conf fidenc idence e va valu lue e (F (Figu igur re e 6) 6).. between them is less than a certain confidence value (Figure 6). Appl. Sci. 2019, 9, 2588 5 of 17 Appl. Sci. 2019, 9, x 5 of 17 Appl. Sci. 2019, 9, x 5 of 17 Figure 6. Distortion points on scanning line. Figure 6. Distortion points on scanning line. Figure 6. Distortion points on scanning line. Data mosaic: Because the laser travels along a straight line, some areas will not be detected Data mosaic: Because the laser travels along a straight line, some areas will not be detected accurately if occlusion or obstruction occurs during the scanning process. Therefore, in order to detect accurately if occlusion or obstruction occurs during the scanning process. Therefore, in order to detect Data mosaic: Because the laser travels along a straight line, some areas will not be detected the actual boundary of the airspace as accurately as possible, it is very important to select a reasonable the act accurately ual bounda if occlusion ry of the or ob airsstruct pace a ion s ac occ curat urs during ely as p th oe sc ssib annin le, itg i pr s ver ocess. There y importf ant ore, to in o sel rder ect to detect a reasonable detection location. For the complex shape of the empty area, we should try to carry out multi-point the actual boundary of the airspace as accurately as possible, it is very important to select a reasonable detection location. For the complex shape of the empty area, we should try to carry out multi-point detection and then splice the point data obtained by multiple detection scans to form an area completely detection location. For the complex shape of the empty area, we should try to carry out multi-point detection and then splice the point data obtained by multiple detection scans to form an area void of detection an point cloud d then sp data. lice The the point d essence ofathe ta obt data ained mosaic by mu islt to iplcompute e detection thescrans t otation o form and an translation area completely void of point cloud data. The essence of the data mosaic is to compute the rotation and completely void of point cloud data. The essence of the data mosaic is to compute the rotation and transformation matrix R, T, which satisfies the following objective functions: translation transformation matrix 𝑅 , 𝑇 , which satisfies the following objective functions: translation transformation matrix 𝑅 , 𝑇 , which satisfies the following objective functions: ( ) [ ] f𝑓 R 𝑅,,𝑇 T =m min in R𝑅∙𝑝p +𝑇T𝑞 q (3 (3) ) i i 𝑓 𝑅,𝑇 min 𝑅∙𝑝 𝑇𝑞 (3) where, 𝑝 and 𝑞 are point clouds that need to be aligned, and the upper formula is a highly where, p and q are point clouds that need to be aligned, and the upper formula is a highly nonlinear where, i 𝑝 and i 𝑞 are point clouds that need to be aligned, and the upper formula is a highly nonlinear problem. The research of the data mosaic focuses on finding a fast and effective solution to problem. nonline The ar pro resear blem. The ch of the res data earch mosaic of the d focuses ata mosa on ic finding focuses on a fast findi and ng a e fective ast andsolution effective so to this lution t problem. o this problem this problem . . Because the point coordinates of the point cloud data obtained by each scan are relative to the Because the point coordinates of the point cloud data obtained by each scan are relative to the Because the point coordinates of the point cloud data obtained by each scan are relative to the coordinate system of the scan, the three-dimensional coordinates of the points obtained by di erent coordinate system of the scan, the three-dimensional coordinates of the points obtained by different coordinate system of the scan, the three-dimensional coordinates of the points obtained by different scanning times (di erent locations or angles of view) are in di erent coordinate systems. Therefore, scanning times (different locations or angles of view) are in different coordinate systems. Therefore, scanning times (different locations or angles of view) are in different coordinate systems. Therefore, we must try to put the three-dimensional point cloud data acquired by multiple scans into a common we must try to put the three-dimensional point cloud data acquired by multiple scans into a common we must try to put the three-dimensional point cloud data acquired by multiple scans into a common coordinate system, to obtain the complete three-dimensional point data in the empty space. This process coordinate system, to obtain the complete three-dimensional point data in the empty space. This coordinate system, to obtain the complete three-dimensional point data in the empty space. This is called a multi-point scanning data mosaic. The principle is shown in Figure 7. process is called a multi-point scanning data mosaic. The principle is shown in Figure 7. process is called a multi-point scanning data mosaic. The principle is shown in Figure 7. Figure 7. Mosaic of multi-point scanning data. Figure 7. Mosaic of multi-point scanning data. Specific cases are as follows: Boreholes #1 and #2 are selected to detect a karst cave twice, and Specific cases are as follows: Boreholes #1 and #2 are selected to detect a karst cave twice, and the Figure 7. Mosaic of multi-point scanning data. the original point clouds detected by two boreholes are obtained through detection. The original original point clouds detected by two boreholes are obtained through detection. The original point point cloud data of borehole #1 are filtered as shown in Figure 8a, and those of borehole #2 are filtered cloud data of borehole #1 are filtered as shown in Figure 8a, and those of borehole #2 are filtered as Specific cases are as follows: Boreholes #1 and #2 are selected to detect a karst cave twice, and as shown in Figure 8b. In each detection process, the borehole coordinates and initial azimuth angle shown in Figure 8b. In each detection process, the borehole coordinates and initial azimuth angle are the original point clouds detected by two boreholes are obtained through detection. The original are recorded. In the process below the probe, the system software automatically records the changes recorded. In the process below the probe, the system software automatically records the changes of point cloud d of depth, aazimuth, an ta of borehole #1 d dip ang are filter le belo ew and d as show then sp n inlices the tw Figure 8a, an o detected d d those of bor ata ine the so hole #ftware to 2 are filtered depth, azimuth, and dip angle below and then splices the two detected data in the software to make make the same detection point position coincide completely. The 3-D point cloud model of the karst as shown in Figure 8b. In each detection process, the borehole coordinates and initial azimuth angle the same detection point position coincide completely. The 3-D point cloud model of the karst cave are recorded. In the process below the probe, the system software automatically records the changes formed by the splicing of boreholes #1 and #2 are shown in Figure 8c,d. The “point cloud creating of depth, azimuth, and dip angle below and then splices the two detected data in the software to make the same detection point position coincide completely. The 3-D point cloud model of the karst Appl. Sci. 2019, 9, 2588 6 of 17 Appl. Sci. 2019, 9, x 6 of 17 cave formed by the splicing of boreholes #1 and #2 are shown in Figure 8c,d. The “point cloud creating entity” of “entity modeling” is used to automatically construct the three-dimensional figure contour of entity” of "entity modeling" is used to automatically construct the three-dimensional figure contour the cave and generate the three-dimensional entity model of the cave (Figure 8). of the cave and generate the three-dimensional entity model of the cave (Figure 8). (a) (b) (c) (d) (e) (f) Figure 8. Construction of three-dimensional real model of karst cave. (a) Primitive point cloud Figure 8. Construction of three-dimensional real model of karst cave. (a) Primitive point cloud of of borehole #1; (b) Primitive point cloud of borehole #2; (c) Point cloud after splicing borehole #1; borehole #1; (b) Primitive point cloud of borehole #2; (c) Point cloud after splicing borehole #1; (d) (d) Point cloud after splicing borehole #2; (e) Point cloud model after splicing boreholes #1 and #2; Point cloud after splicing borehole #2; (e) Point cloud model after splicing boreholes #1 and #2; (f) (f) Three-dimensional solid model of karst cave. Three-dimensional solid model of karst cave. Appl. Sci. 2019, 9, x 7 of 17 Appl. Sci. 2019, 9, 2588 7 of 17 3. General Situation of Engineering Geology and Location and Quantitative Exploration Method 3. General Situation of Engineering Geology and Location and Quantitative Exploration Method of Jinan Metro’s Karst Cave of Jinan Metro’s Karst Cave Traffic congestion in Jinan ranks first in the country all year round, and it is urgent to build the Trac congestion in Jinan ranks first in the country all year round, and it is urgent to build the subway. Jinan Metro proposed the planning of the urban core area express line (R line) and the central subway. Jinan Metro proposed the planning of the urban core area express line (R line) and the central city general line (M line). The express line consists of three lines: R1, R2, and R3. The central city’s city general line (M line). The express line consists of three lines: R1, R2, and R3. The central city’s general line includes 7 lines, the loop line and the M1 to M6 lines, forming a "loop + radiation" line general line includes 7 lines, the loop line and the M1 to M6 lines, forming a “loop + radiation” line network structure. In 2015, the R1 line of the first line of Jinan Metro officially started. Since then, network structure. In 2015, the R1 line of the first line of Jinan Metro ocially started. Since then, three lines in total have been started. three lines in total have been started. Jinan is also famous for its spring water. The origin of the spring water is mainly due to the Jinan is also famous for its spring water. The origin of the spring water is mainly due to the barrier of the northern impermeable magmatic rock in the process of the northward runoff of karst barrier of the northern impermeable magmatic rock in the process of the northward runo of karst water, and then the groundwater flows out in the limestone sky window under the large pressure of water, and then the groundwater flows out in the limestone sky window under the large pressure of the water head. Therefore, the construction of Jinan Metro needs to pass through a large number of the water head. Therefore, the construction of Jinan Metro needs to pass through a large number of limestone formations with strong karst development. In order to ensure the rapid and safe limestone formations with strong karst development. In order to ensure the rapid and safe construction construction of the subway, it is very necessary to carry out meticulous exploration and treatment of of the subway, it is very necessary to carry out meticulous exploration and treatment of karst caves in karst caves in karst areas. karst areas. 3.1. General Situation of Engineering Geology 3.1. General Situation of Engineering Geology The length of the Wangfu village station to the Dayang village station on the R1 line of Jinan The length of the Wangfu village station to the Dayang village station on the R1 line of Jinan Metro Metro is about 2033 m. This subway section passes through the middle weathered-limestone is about 2033 m. This subway section passes through the middle weathered-limestone development development area. The length of the left line tunnel through limestone is about 725 m, and the length area. The length of the left line tunnel through limestone is about 725 m, and the length of the right of the right line tunnel is about 798 m. Preliminary investigation data show that the uniaxial line tunnel is about 798 m. Preliminary investigation data show that the uniaxial compressive strength compressive strength of moderately weathered limestone is 34.2–83.2 Mpa. The geological boreholes of moderately weathered limestone is 34.2–83.2 Mpa. The geological boreholes along the tunnel reveal along the tunnel reveal karst caves in the middle weathered-limestone section. The main source of karst caves in the middle weathered-limestone section. The main source of groundwater is limestone groundwater is limestone fracture karst water, which is the largest water area in the central and fracture karst water, which is the largest water area in the central and western parts of Jinan. The section western parts of Jinan. The section is a rich water area, where the water supply is large, and the is a rich water area, where the water supply is large, and the groundwater is confined (Figure 9). groundwater is confined (Figure 9). Figure 9. Geologic profile of the distance between the Wangfu village station and the Dayang Figure 9. Geologic profile of the distance between the Wangfu village station and the Dayang village village station. station. The hydrogeological map shows that the interval through the weathered-limestone section is the The hydrogeological map shows that the interval through the weathered-limestone section is largest water area in the central and western part of Jinan. The output of a single well of fractured the largest water area in the central and western part of Jinan. The output of a single well of fractured karst water is more than 10,000 m /d, which indicates that this section is a water-rich area with large karst water is more than 10,000 m /d, which indicates that this section is a water-rich area with large water recharge and confined groundwater (Figure 10). The figure below shows one of the exposed water recharge and confined groundwater (Figure 10). The figure below shows one of the exposed karst caves (Figure 11). karst caves (Figure 11). Appl. Sci. 2019, 9, 2588 8 of 17 Appl. Sci. 2019, 9, x 8 of 17 Appl. Sci. 2019, 9, x 8 of 17 Figure 10. Figure 10. G Ge eo ollogic profil ogic profile of e of t th he dis e dist tance bet ance betw ween the een the Wangfu Wangfu village village stati statio on and the Day n and the Daya ang village ng village Figure 10. Geologic profile of the distance between the Wangfu village station and the Dayang station. station. village station. Figure 11. Exposed water-bearing karst cave. Figure 11. Exposed water-bearing karst cave. Figure 11. Exposed water-bearing karst cave. 3.2. Location Exploration Method of Karst Cave 3. 3.2. 2. Locati Location on E Expl xplora orat tiio on n Met Meth hod od of of K Ka arst rst C Ca ave ve Table 1 mainly introduces six common geophysical methods under di erent detection principles. Ta Table ble 11 mainly introduces six mainly introduces six common geop common geophy hysic sicaal method l methods under s under different detection different detection Each of them has di erent characteristics. principles. Each of them h principles. Each of them ha as different ch s different char aracterist acteristics. ics. In accordance with the characteristics of geophysical prospecting and the engineering geology of the R1 line, the most suitable geophysical method was selected. First, the subway was built in the urban Table 1. Table 1. The The characteristi characteristic cs s of of different g different ge eop ophy hysical m sical me ethod thods. s. area, where the surface soil is thicker. The seismic wave reflection method and the ground-penetrating Prediction met Prediction meth hod od Characteristic Characteristic radar method lead to more disturbances. Therefore, these two methods are not applicable. Second, The dete The detection a ction accuracy is ccuracy is higher in the range higher in the range of 20–200 mete of 20–200 meters and the rs and the dete detection ction The seismic wa The seismic wave ve because of the abundance of groundwater in the interval, the microgravity method is not applicable. effect effect is is better f better fo or karst cav r karst cave es. s. However, However, the a the ad daptability aptability to t to th hick overbu ick overburde rden n soil soil reflection reflection method [20] method [20] Third, the upper part of the subway line is a highway, and the high-density electrical method leads is poor is poor, and , and en energy attenu ergy attenuation is ation is faster. faster. to certain destructiveness on the road surface. Finally, the transient electromagnetic method is more The land The land sonar method sonar method The predict The predictiion on of medium and of medium and small small cav cave ern rns s and fractu and fractured z red zo ones i nes is s eff effe ecti ctiv ve, bu e, but t suitable for the comparison between the land sonar method and the transient electromagnetic method. [21] [21] the velo the velocity city of of each lay each laye er r ca cannot be accurately obtained. nnot be accurately obtained. No filling cavern or water-rich cavern with the obvious electrical difference with The principle of the transient No fi electr lling omagnetic cavern or water-ric method h cavern with is that a pulsed the obviou magnetic s elec field trical is differenc transmitted e with to The high-density The high-density su surrou rroun nding ding rock rock stratu stratum m is is g good. ood. It It can onl can only y be qu be qualitat alitative ive bu but not t not the front of the working face using an ungrounded line. When the current in the transmission line electrical method [22] electrical method [22] quantitatively explored. quantitatively explored. is abruptly disconnected, the two eddy fields will be excited to maintain the magnetic field (that is, It is sensitive to large water-filled low-resistivity zones and has the ability to It is sensitive to large water-filled low-resistivity zones and has the ability to one field) before the disconnected current, the size, and attenuation of the two eddy current field The transient The transient penetrate low-resistance coverage. The depth of detection is large. However, the penetrate low-resistance coverage. The depth of detection is large. However, the and the electricity of the surrounding medium. This is related to the electrical distribution of the electromagnetic method electromagnetic method resolu resolution of tion of e em mpty caves or pty caves or dry-filling kars dry-filling karst cave t caves s is is not e not en nou ough, so it gh, so it is is diffi difficu cult lt surrounding [23,24] [23,24] medium. The variation of the secondary field with time is observed during the first to di to distingu stinguish. ish. field intermittence. After processing, the electric property, the scale, and the form of the underground In the high-resistivity area, the detection depth is 20–30 meters and the detection In the high-resistivity area, the detection depth is 20–30 meters and the detection The ground-penetrating The ground-penetrating medium can be understood to achieve the aim of detecting the target. effect is good for karst caves and faults. However, it is easy to be affected by the effect is good for karst caves and faults. However, it is easy to be affected by the radar method [ radar method [25,26] 25,26] su surface so rface soil il, an , and the d the detec detecttion ion depth i depth is s g gr reatl eatly y redu reduced. ced. Under flat terrain, it is widely used in karst investigation. However, factors such Under flat terrain, it is widely used in karst investigation. However, factors such The microgravity The microgravity as topography fluctuation, sediment thickness, and fluctuation of diving surface as topography fluctuation, sediment thickness, and fluctuation of diving surface method [27] method [27] are relative are relatively l ly la arge. rge. Appl. Sci. 2019, 9, 2588 9 of 17 Table 1. The characteristics of di erent geophysical methods. Prediction Method Characteristic The detection accuracy is higher in the range of 20–200 m and the The seismic wave reflection detection e ect is better for karst caves. However, the adaptability to thick method [20] overburden soil is poor, and energy attenuation is faster. The prediction of medium and small caverns and fractured zones is The land sonar method [21] e ective, but the velocity of each layer cannot be accurately obtained. No filling cavern or water-rich cavern with the obvious electrical The high-density electrical di erence with surrounding rock stratum is good. It can only be method [22] qualitative but not quantitatively explored. It is sensitive to large water-filled low-resistivity zones and has the ability The transient electromagnetic to penetrate low-resistance coverage. The depth of detection is large. method [23,24] However, the resolution of empty caves or dry-filling karst caves is not enough, so it is dicult to distinguish. In the high-resistivity area, the detection depth is 20–30 m and the The ground-penetrating radar detection e ect is good for karst caves and faults. However, it is easy to be method [25,26] a ected by the surface soil, and the detection depth is greatly reduced. Under flat terrain, it is widely used in karst investigation. However, The microgravity method [27] factors such as topography fluctuation, sediment thickness, and fluctuation of diving surface are relatively large. The main reason for choosing high-density resistivity method and transient electromagnetic method for comprehensive detection is that the resistivity of underground rock is mainly influenced by mineral composition, water content, and temperature of rock. These complex factors result in the instability of rock resistivity and change in a large range. When there are fissures or fault zones in underground rocks and water-rich rocks with water-conducting channels, the resistivity of natural rocks located in these structural areas will be significantly reduced. There are obvious electrical di erences with surrounding strata. Previous geological survey and site exposure show that it has the geological and physical basis of electrical detection. Each geophysical prospecting method has its own advantages and disadvantages. It is often dicult to satisfy the requirement of detection accuracy by using a single method. The combination of various geophysical methods can complement each other and verify each other. We have made a total of 500 meters of detection, from L30+900–L31+450. Figure 12b transient electromagnetic (TEM) locations are from L30+900–L31+40 and L31+110–L31+290, totaling 500 m. Five sets of high-density resistivity have been made, each of which is 100 m. Figure 12a shows the third group, which is from L31+150–L31+250. By means of resistivity anomaly, areas with strong karst development are detected. In these areas, we determined the locations of five boreholes, h1(110), h2 (230), h3 (280), h4 (315), and h5 (350) in Figure 12b, respectively. From the results of core drilling, it can be seen that all five boreholes encounter karst caves. Appl. Sci. 2019, 9, x 10 of 17 Appl. Sci. 2019, 9, x 10 of 17 Appl. Sci. 2019, 9, 2588 10 of 17 (a) (a) (b) (b) Figure 12. Comprehensive interpretation diagram of the high-density resistivity method and transient Figure 12. Comprehensive interpretation diagram of the high-density resistivity method and transient Figure 12. Comprehensive interpretation diagram of the high-density resistivity method and transient electromagnetic. (a) The result of high-density resistivity method; (b) The result of transient electromagnetic. (a) The result of high-density resistivity method; (b) The result of transient electromagnetic. (a) The result of high-density resistivity method; (b) The result of transient electromagnetic. electromagnetic. electromagnetic. The core of each drill is shown in Figure 13. The core of each drill is shown in Figure 13. The core of each drill is shown in Figure 13. (a) (b) (a) (b) (c) (d) (c) (d) Figure 13. Drilling core drawing. (a) Coring of hole h1; (b) Coring of hole h2; (c) Coring of hole h3; Figure 13. Drilling core drawing. (a) Coring of hole h1; (b) Coring of hole h2; (c) Coring of hole h3; Figure 13. Drilling core drawing. (a) Coring of hole h1; (b) Coring of hole h2; (c) Coring of hole h3; (d) Coring of hole h4; (e) Coring of hole h5. (d) Coring of hole h4; (e) Coring of hole h5. (d) Coring of hole h4; (e) Coring of hole h5. Appl. Sci. 2019, 9, x 11 of 17 Appl. Sci. 2019, 9, 2588 11 of 17 Appl. Sci. 2019, 9, x 11 of 17 Using five target drilling points, through the improvement of exploration equipment and Using five target drilling points, through the improvement of exploration equipment and exploration method, using panoramic probe sampling, combined with automatic ray compensation Using five target drilling points, through the improvement of exploration equipment and exploration method, using panoramic probe sampling, combined with automatic ray compensation and automatic positioning technology, the acquisition of geological images in a borehole dark exploration method, using panoramic probe sampling, combined with automatic ray compensation and and automatic positioning technology, the acquisition of geological images in a borehole dark environment was achieved. Long distance accurate detection and real imaging of disaster sources automatic positioning technology, the acquisition of geological images in a borehole dark environment environment was achieved. Long distance accurate detection and real imaging of disaster sources such as karst cave were realized by 3D laser scanning (MDL, Edinburgh, Scotland). was achieved. Long distance accurate detection and real imaging of disaster sources such as karst cave such as karst cave were realized by 3D laser scanning (MDL, Edinburgh, Scotland). The characteristics of 3D laser scanning (Figure 14) are as follows: (1) Rapidity: The spatial were realized by 3D laser scanning (MDL, Edinburgh, Scotland). The characteristics of 3D laser scanning (Figure 14) are as follows: (1) Rapidity: The spatial information of the karst cave can be obtained quickly, and the coordinate information of the karst The characteristics of 3D laser scanning (Figure 14) are as follows: (1) Rapidity: The spatial information of the karst cave can be obtained quickly, and the coordinate information of the karst cave surface can be measured in time. (2) Non-contact: We can scan the targets in a non-contact way. information of the karst cave can be obtained quickly, and the coordinate information of the karst cave surface can be measured in time. (2) Non-contact: We can scan the targets in a non-contact way. (3) Penetration: Under the water cut condition of the cave, it can cross the water body and reach the cave surface can be measured in time. (2) Non-contact: We can scan the targets in a non-contact way. (3) Penetration: Under the water cut condition of the cave, it can cross the water body and reach the target surface. (4) Real-time, dynamic, and active: The target information is obtained by the reflection (3) Penetration: Under the water cut condition of the cave, it can cross the water body and reach the target surface. (4) Real-time, dynamic, and active: The target information is obtained by the reflection of light emitted by itself. It cannot be constrained by time and space, and the beam is quasi-parallel target surface. (4) Real-time, dynamic, and active: The target information is obtained by the reflection of of light emitted by itself. It cannot be constrained by time and space, and the beam is quasi-parallel light, which avoids the inherent optical distortion error of conventional optical measurement. (5) light emitted by itself. It cannot be constrained by time and space, and the beam is quasi-parallel light, light, which avoids the inherent optical distortion error of conventional optical measurement. (5) High density and high precision: Laser scanning obtains target characteristics in a high-density and which avoids the inherent optical distortion error of conventional optical measurement. (5) High density High density and high precision: Laser scanning obtains target characteristics in a high-density and high-precision way. The laser point cloud is composed of point position coordinate data. Using a and high precision: Laser scanning obtains target characteristics in a high-density and high-precision way. high-precision way. The laser point cloud is composed of point position coordinate data. Using a large lattice and a certain density grid to describe the entity information, the target information can The laser point cloud is composed of point position coordinate data. Using a large lattice and a certain large lattice and a certain density grid to describe the entity information, the target information can be described more accurately. density grid to describe the entity information, the target information can be described more accurately. be described more accurately. Three-dimensional laser scanning devices are placed in five boreholes, as shown in Figure 15. Three-dimensional laser scanning devices are placed in five boreholes, as shown in Figure 15. Three-dimensional laser scanning devices are placed in five boreholes, as shown in Figure 15. (a) (b) (c) (a) (b) (c) Figure 14. Laser scanning equipment and operation interface. (a,b) Laser scanning equipment; (c) Figure 14. Figure 14. Laser scanning eq Laser scanning equipment uipment and operation interf and operation interface. ace. (a,b() La a,b)se Laser r scanning scanning equiequipment; pment; (c) operation interface. operation inter (c) operation interface. face. Figure 15. Karst cave distribution map. Figure 15. Karst cave distribution map. Figure 15. Karst cave distribution map. 3.3. Three-Dimensional Model of Karst Cave 3.3. Three-Dimensional Model of Karst Cave 3.3. Three-Dimensional Model of Karst Cave h1 measured a cave about 1 m high at about 19.1 m underground, with a volume of about 2 cubic h1 measured a cave about 1 m high at about 19.1 m underground, with a volume of about 2 cubic h1 measured a cave about 1 m high at about 19.1 m underground, with a volume of about 2 cubic meters. The three-dimensional model of the cave is shown in Figure 16. meters. The three-dimensional model of the cave is shown in Figure 16. meters. The three-dimensional model of the cave is shown in Figure 16. Appl. Sci. 2019, 9, 2588 12 of 17 Appl. Sci. 2019, 9, x 12 of 17 Appl. Sci. 2019, 9, x 12 of 17 Appl. Sci. 2019, 9, x 12 of 17 Figure 16. The three-dimensional model of the cave (h1). Figure 16. The three-dimensional model of the cave (h1). Figure 16. The three-dimensional model of the cave (h1). Figure 16. The three-dimensional model of the cave (h1). h2 h2 m measur easure ed d a a cave cave about about 1 1.5 .5 m m high high at at a about bout 21 m 21 m un under dergro ground, und, w with ith a volum a volume e of ab of about out 3 3 cub cubic ic h2 measured a cave about 1.5 m high at about 21 m underground, with a volume of about 3 cubic h2 measured a cave about 1.5 m high at about 21 m underground, with a volume of about 3 cubic meters. meters. The t The thr hree-d ee-dimensional imensional model of model of t the he cave cave is is sh shown own in in Figur Figure e 1 17 7.. meters. The three-dimensional model of the cave is shown in Figure 17. meters. The three-dimensional model of the cave is shown in Figure 17. Figure 17. The three-dimensional model of the cave (h2). Figure 17. The three-dimensional model of the cave (h2). Figure 17. The three-dimensional model of the cave (h2). Figure 17. The three-dimensional model of the cave (h2). h3 measured the beaded cave at about 19–22.5 m from the ground, with a volume of about 3.44 h3 measured the beaded cave at about 19–22.5 m from the ground, with a volume of about 3.44 h3 measured the beaded cave at about 19–22.5 m from the ground, with a volume of about 3.44 h3 measured the beaded cave at about 19–22.5 m from the ground, with a volume of about 3.44 and 3.6 cubic meters, respectively. The three-dimensional model of the cave is shown in Figure 18. and 3.6 cubic meters, respectively. The three-dimensional model of the cave is shown in Figure 18. and 3.6 cubic meters, respectively. The three-dimensional model of the cave is shown in Figure 18. and 3.6 cubic meters, respectively. The three-dimensional model of the cave is shown in Figure 18. Figure 18. The three-dimensional model of the cave (h3). Figure 18. The three-dimensional model of the cave (h3). Figure 18. The three-dimensional model of the cave (h3). Figure 18. The three-dimensional model of the cave (h3). h4 measured the cavern at about 2.8–20.5 m from the ground, with a volume of about 9 cubic h4 measured the cavern at about 2.8–20.5 m from the ground, with a volume of about 9 cubic h4 measured the cavern at about 2.8–20.5 m from the ground, with a volume of about 9 cubic h4 measured the cavern at about 2.8–20.5 m from the ground, with a volume of about 9 cubic meters. The three-dimensional model of the cave is shown in Figure 19. meters. The three-dimensional model of the cave is shown in Figure 19. meters. The three-dimensional model of the cave is shown in Figure 19. meters. The three-dimensional model of the cave is shown in Figure 19. Appl. Sci. 2019, 9, x 13 of 17 Appl. Sci. 2019, 9, x 13 of 17 Appl. Sci. 2019, 9, x 13 of 17 Appl. Sci. 2019, 9, x 13 of 17 Appl. Sci. 2019, 9, 2588 13 of 17 Appl. Sci. 2019, 9, x 13 of 17 Appl. Sci. 2019, 9, x 13 of 17 Figure 19. The three-dimensional model of the cave (h4). Figure 19. The three-dimensional model of the cave (h4). Figure 19. The three-dimensional model of the cave (h4). Figure 19. The three-dimensional model of the cave (h4). h5 measured caves at about 16–21.5 m from the ground with a vol ume of about 2.1–2.7 cubic h5 measured caves at about 16–21.5 m from the ground with a volume of about 2.1–2.7 cubic h5 measured caves at about 16–21.5 m from the ground with a volume of about 2.1–2.7 cubic Figure 19. The three-dimensional model of the cave (h4). h5 measured caves at about 16–21.5 m from the ground with a volume of about 2.1–2.7 cubic Figure 19. The three-dimensional model of the cave (h4). meters. The three-dimensional model of the cave is shown in Figure 20. meters. The three-dimensional model of the cave is shown in Figure 20. Figure 19. The three-dimensional model of the cave (h4). meters. The three-dimensional model of the cave is shown in Figure 20. meters. The three-dimensional model of the cave is shown in Figure 20. h5 measured caves at about 16–21.5 m from the ground with a volume of about 2.1–2.7 cubic h5 measured caves at about 16–21.5 m from the ground with a volume of about 2.1–2.7 cubic h5 measured caves at about 16–21.5 m from the ground with a volume of about 2.1–2.7 cubic meters. The three-dimensional model of the cave is shown in Figure 20. meters. The three-dimensional model of the cave is shown in Figure 20. meters. The three-dimensional model of the cave is shown in Figure 20. Figure 20. Figure 20. The The three-dimensio three-dimensio nal model nal model of th of th e cave e cave (h5). (h5). Figure 20. The three-dimensional model of the cave (h5). Figure 20. The three-dimensional model of the cave (h5). Figure 20. The three-dimensional model of the cave (h5). Figure 20. The three-dimensional model of the cave (h5). The volume of each cave is shown in Table 2. The volume of each cave is shown in Table 2. The volume of each cave is shown in Table 2. Figure 20. The three-dimensional model of the cave (h5). The volume of each cave is shown in Table 2. The volume of each cave is shown in Table 2. The volume of each cave is shown in Table 2. Table 2. The volume of each cave. Table 2. The volume of each cave. Table 2. The volume of each cave. The volume of each cave is shown in Table 2. Table 2. The volume of each cave. Table 2. The volume of each cave. Table 2. The volume of each cave. Drill Hole Limestone Cave Volume (m ) Drill Hole Limestone Cave Volume (m 3) Drill Hole Limestone Cave Volume (m3 ) Drill Hole Limestone Cave 3 Volume (m ) Drill Hole Table 2. L The imesto volume of ea ne Cave ch cave. Volume (m ) Drill Hole Limestone Cave Volume (m ) Drill Hole Limestone Cave Volume (m ) h1 3.02 h1 3.02 h1 3.02 h1 3.02 h1 3.02 h1 3.02 h1 3.02 h2 3.89 h2 h2 3. 3. 89 89 h2 h2 3.89 3.89 h2 3.89 h2 3.89 3.44 3.44 3.44 3.44 3.44 3.44 h3 h3 h3 h3 h3 h3 3.44 3.66 3.66 3.66 3.66 3.66 3.66 h3 3.66 Appl. Sci. 2019, 9, 2588 14 of 17 Table 2. Cont. Appl. Sci. 2019, 9, x 14 of 17 Appl. Sci. 2019, 9, x 14 of 17 Appl. Appl. Sci. Sci. 2019 2019, , 9 9, x , x 14 of 14 of 17 17 Appl. Sci. 2019, 9, x 14 of 17 Drill Hole Limestone Cave Volume (m ) h4 3.84 h4 h4 h4 h4 3.84 3. 3. 3.84 84 84 h4 3.84 3.15 3.15 3. 3. 3.15 15 15 3.15 h5 h5 3.7 h5 h5 h5 3.7 3.7 3. 3.7 7 h5 3.7 3.29 3.29 3. 3. 3.29 29 29 3.29 At the same time, the high-definition camera function was mounted on the laser three- At the same time, the high-definition camera function was mounted on the laser three-dimensional At At At t t thh he s e s e saaame me me t t tiiime, me, me, t t thh he h e h e hiiigh-de gh-de gh-defin fin finitit ition ion ion camer camer cameraaa functi functi function was m on was m on was mooounted on the la unted on the la unted on the laser three- ser three- ser three- At the same time, the high-definition camera function was mounted on the laser three- dimensional detection system. The results are shown in Figure 21. detection dimensional system. detection sy The results stem. The are shown resu in lts are Figur shown e 21. in Figure 21. dimensional dimensional detection sy detection system. The stem. The re resu sults are lts are shown shown in Fig in Figu ure re 21. 21. dimensional detection system. The results are shown in Figure 21. Figure 21. Intra-hole photography. Figure Figure 21. 21. Intra-hole Intra-hole photography. photography. Figure 21. Figure 21. Intr Intra-hole photography. a-hole photography. Figure 21. Intra-hole photography. 4. T 4. reatment Treatment of Karst of Kars Cave t Cave 4. 4. 4. T T Trr re e ea a atm tm tment ent ent of Kars of Kars of Karstt t C C Ca a av v ve e e 4. Treatment of Karst Cave During the construction of metro, it is easy to cause the risk of ground subsidence. If there are During the construction of metro, it is easy to cause the risk of ground subsidence. If there are Duri Duri During the constructi ng the constructi ng the construction of on of on of metro, i metro, i metro, itt t iiiss s ea ea easy to sy to sy to cc ca a ause use use the risk o the risk o the risk off f gr gr ground subside ound subside ound subsiden n nce. If there ce. If there ce. If there are are are During the construction of metro, it is easy to cause the risk of ground subsidence. If there are kars ka t crst ca aves ves above the sub above the subway,w tha eyr, the isk ofrig sk of roun ground d collapsc eoillapse ncrease incre s sha arse pls sh y. Tarply. hereforTherefore e, the abo,v the above e karst ka ka karst ca rst ca rst caves above the sub ves above the sub ves above the subw w waa ay y y, the , the , the ri ri risk of sk of sk of ground ground ground cc co o ollapse llapse llapse incre incre increaa ase se ses sh s sh s sharply. arply. arply. Therefore Therefore Therefore,,, the above the above the above karst caves above the subway, the risk of ground collapse increases sharply. Therefore, the above karst caves need to be harnessed. Sufficient safety distance should be ensured for karst caves under caves need to be harnessed. Sufficient safety distance should be ensured for karst caves under metro. kar kar karss st caves n t caves n t caves need to be har eed to be har eed to be harn n nessed essed essed... Suffic Suffic Sufficient safety ient safety ient safety d d diiistance sho stance sho stance shou u uld ld ld be ensur be ensur be ensured for kar ed for kar ed for karss st cave t cave t caves under s under s under karst caves need to be harnessed. Sufficient safety distance should be ensured for karst caves under If th metro. If the sa e safety distanf ce ety di from sta th ne ce f floro om r is the toofs lo m or is too all, it is sm easal y l, to itc is ea ausesy to the scau ettle se m the settl ent of th ement of e subwa the subway y tunnel. metro. If the sa metro. If the sa metro. If the saff fe e ety di ty di ty dista sta stan n nce f ce f ce fr r rom om om the the the ff fll lo o oor is too or is too or is too sm sm smal al all, l, l, ii itt t is ea is ea is easy to sy to sy to cau cau caus s se e e the settl the settl the settlement of ement of ement of the subway the subway the subway metro. If the safety distance from the floor is too small, it is easy to cause the settlement of the subway tunnel. According to the design experience, it is necessary to treat the floor karst cave within twice tt tu u unnel. nnel. nnel. Accor Accor Accord d ding t ing t ing to o o t t th h he d e d e de e esign sign sign experi experi experie e en n nce, it ce, it ce, it is ne is ne is necessary to trea cessary to trea cessary to treat the f t the f t the fllloor oor oor karst ca karst ca karst cave wi ve wi ve withi thi thin n n twi twi twicc ce e e tunnel. According to the design experience, it is necessary to treat the floor karst cave within twice the diameter of the tunnel. For the karst caves on both sides of metro tunnel, the disturbance effect of the diameter of the tunnel. For the karst caves on both sides of metro tunnel, the disturbance effect of the dia the diam meter eter of of the tunnel. the tunnel. For the ka For the karst rst ca caves on bo ves on both si th sides of metro tunnel des of metro tunnel, , the the disturb disturba ance nce e effect ffect of of the diameter of the tunnel. For the karst caves on both sides of metro tunnel, the disturbance effect of shield excavation is mainly considered. According to engineering experience, when shield machine shie shie shield exc ld exc ld exca a ava va vatt tiiion is m on is m on is ma a ain in inly ly ly conside conside considerr red. ed. ed. Accordin Accordin According to engineer g to engineer g to engineering ing ing e e ex x xperience, w perience, w perience, wh h hen shie en shie en shield m ld m ld ma a achine chine chine shield excavation is mainly considered. According to engineering experience, when shield machine is excavated, the influence of karst caves beyond 5 m on both sides of the tunnel is small, only the is excavated, the influence of karst caves beyond 5 m on both sides of the tunnel is small, only the is excav is excava ated, ted, the in the influence fluence of of kar kars st c t ca aves beyond ves beyond 5 5 m m on both si on both sides of the tu des of the tunnel is nnel is smal small, l, only the only the is excavated, the influence of karst caves beyond 5 m on both sides of the tunnel is small, only the Appl. Sci. 2019, 9, 2588 15 of 17 According to the design experience, it is necessary to treat the floor karst cave within twice the diameter of the tunnel. For the karst caves on both sides of metro tunnel, the disturbance effect of shield excavation is Appl. Sci. 2019, 9, x 15 of 17 mainly considered. According to engineering experience, when shield machine is excavated, the influence of karst caves beyond 5 m on both sides of the tunnel is small, only the karst caves within 5 m need karst caves within 5 m need to be treated. Reserve special holes for karst treatment in the segment to be treated. Reserve special holes for karst treatment in the segment structure for newly discovered structure for newly discovered karst caves during tunnel excavation and areas where settlement karst caves during tunnel excavation and areas where settlement exceeds, or abnormality occurs in the exceeds, or abnormality occurs in the later stages of the tunnel. Supplementary drilling is carried out later stages of the tunnel. Supplementary drilling is carried out in every 10 annular segments along the in every 10 annular segments along the line, and the drilling depth is twice as far down as the tunnel line, and the drilling depth is twice as far down as the tunnel bottom. According to the drilling results, bottom. According to the drilling results, grouting filling is carried out at the tunnel bottom to ensure grouting filling is carried out at the tunnel bottom to ensure the safety of operation. the safety of operation. If a karst cave is found, it can be treated. For a karst cave whose diameter is less than 1 m, If a karst cave is found, it can be treated. For a karst cave whose diameter is less than 1 m, the the volume is smaller and the cement slurry needed for filling is less. Pressure grouting with 1:1 volume is smaller and the cement slurry needed for filling is less. Pressure grouting with 1:1 cement cement slurry is directly applied to non-filled and semi-filled karst caves whose height is not more than slurry is directly applied to non-filled and semi-filled karst caves whose height is not more than 1 m. 1 m. For karst caves with a larger diameter, the volume required is larger. Sand blowing treatment For karst caves with a larger diameter, the volume required is larger. Sand blowing treatment can be can be carried out first, and then grouting reinforcement can be carried out. The small void of sand carried out first, and then grouting reinforcement can be carried out. The small void of sand is is conducive to cement deposition, reduces the di usion of cement slurry in the range of ine ective conducive to cement deposition, reduces the diffusion of cement slurry in the range of ineffective di usion, and e ectively reduces the filling cost while guaranteeing the strength. diffusion, and effectively reduces the filling cost while guaranteeing the strength. Through the limestone section, the uniaxial saturated compressive strength of limestone lies in the Through the limestone section, the uniaxial saturated compressive strength of limestone lies in range of 34–83 MPa, the buried depth of the left tunnel is 14.7–25.4 m, and the buried depth of the right the range of 34–83 MPa, the buried depth of the left tunnel is 14.7–25.4 m, and the buried depth of the tunnel is 14.7–25.2 m. The current maximum water level is 5.2 m below the ground, the anti-floating right tunnel is 14.7–25.2 m. The current maximum water level is 5.2 m below the ground, the anti- waterproof level is 1.9 m below the ground, and the maximum water head height at the bottom of the floating waterproof level is 1.9 m below the ground, and the maximum water head height at the left and right tunnels is 23.5 m during the whole operation period. When the allowable opening of bottom of the left and right tunnels is 23.5 m during the whole operation period. When the allowable segment joint is 6 mm, the elastic gasket can still resist water pressure of 0.8 MPa. Considering the high opening of segment joint is 6 mm, the elastic gasket can still resist water pressure of 0.8 MPa. strength of rocks, the development of karst and fractured zones, the abundant karst water, the dicult Considering the high strength of rocks, the development of karst and fractured zones, the abundant control of tunneling posture during shield tunneling, and the diculty in reaching the ideal state of karst water, the difficult control of tunneling posture during shield tunneling, and the difficulty in segment assembling quality, in order to improve the waterproofing ability of shield segments, flexible reaching the ideal state of segment assembling quality, in order to improve the waterproofing ability seams with full rings are used in rock-piercing sections (Figure 22). of shield segments, flexible seams with full rings are used in rock-piercing sections (Figure 22). Figure 22. Figure 22. Drawing of grouting borehole. Drawing of grouting borehole. 5. Conclusions 5. Conclusions 1. The apparent resistivity of karst caves is higher than that of relatively intact strata. In a complex 1. The apparent resistivity of karst caves is higher than that of relatively intact strata. In a complex urban environment, high-density electrical method and transient electromagnetic method have urban environment, high-density electrical method and transient electromagnetic method have high resolution for karst caves. Through the results of geophysical prospecting, targeted drilling high resolution for karst caves. Through the results of geophysical prospecting, targeted drilling can be carried out to avoid blind drilling. can be carried out to avoid blind drilling. 2. The laser point cloud is composed of point position coordinate data. Using a large lattice and a certain density grid to describe the entity information, the target information can be described more accurately. Making full use of the target drill hole and fine scanning of the cave via a 3-D automatic laser scanner, parameters such as the real shape and volume of the cave were obtained. Appl. Sci. 2019, 9, 2588 16 of 17 2. The laser point cloud is composed of point position coordinate data. Using a large lattice and a certain density grid to describe the entity information, the target information can be described more accurately. Making full use of the target drill hole and fine scanning of the cave via a 3-D automatic laser scanner, parameters such as the real shape and volume of the cave were obtained. 3. According to the construction experience and design principle, the treatment scope and method of karst caves in di erent locations are determined. The karst caves above the metro must be filled. The karst caves below the tunnel within twice the diameter need to be filled. The karst caves within 5 m on both sides of the tunnel need to be filled. When the diameter of karst cave is less than 1 m, it can be filled with cement slurry directly. When the diameter of karst cave is larger than 1 m, it needs to be filled with sand before grouting. Author Contributions: Conceptualization, J.W. and L.L.; Methodology, S.S. (Shaoshuai Shi); Software, S.S. (Shangqu Sun); Validation, J.W., L.L. and S.S. (Shaoshuai Shi); Formal Analysis, J.W.; Investigation, S.S. (Shaoshuai Shi); Resources, J.W.; Data Curation, S.S. (Shangqu Sun); Writing—Original Draft Preparation, X.B.; Writing—Review & Editing, Y.Z.; Visualization, X.B.; Supervision, L.L.; Project Administration, L.L.; Funding Acquisition, J.W. Funding: The work is supported by National Natural Science Foundation of China (Grant No. 51809158, 51609129, 51809157), Shandong Provincial Natural Science Foundation, China (Grant No. ZR2018BEE045), China Postdoctoral Science Foundation (2018M630780). Conflicts of Interest: The authors declare no conflict of interest. References 1. Sun, S.; Li, L.; Wang, J.; Shi, S.; Song, S.; Fang, Z.; Ba, X.; Jin, H. Karst Development Mechanism and Characteristics Based on Comprehensive Exploration along Jinan Metro, China. Sustainability 2018, 10, 3383. [CrossRef] 2. Foley, A.E. The Use and Development of Some Groundwater Tracing Techniques for Wellhead Protection: Studies from the Corallian Limestone of Yorkshire. Ph.D. Thesis, University College London, 2006. 3. Hui, G.; Xu, J. A numerical simulation of impact of groundwater seepage on temperature distribution in karst collapse pillar. Arab. J. Geosci. 2017, 10, 10. 4. Li, S.; Liu, B.; Nie, L.; Liu, Z.; Tian, M.; Wang, S.; Su, M.; Guo, Q. Detecting and monitoring of water inrush in tunnels and coal mines using direct current resistivity method: A review. J. Rock Mech. Geotech. Eng. 2015, 7, 469–478. [CrossRef] 5. Zhong, S.; Wang, R. New Landsonar Method for Survey of Ground in Busy Town, Karst Caves in Mountain and Sea Bottom on Water. J. Eng. Geol. 2013, 21, 422–432. 6. Peng, C. The Combined Application of Seismic Imaging Method and High-Density Electric Method to the Survey of Karst CollapseAreas. Chin. J. Eng. Geophys. 2016, 13, 60–63. 7. Knapp, R.W.; Steeples, D.W. High-resolution common-depth-point reflection profiling: Field acquisition parameter design. Geophysics 1986, 51, 283–294. [CrossRef] 8. Carbonel, D.; Rodríguez, V.; Gutiérrez, F.; McCalpin, J.P.; Linares, R.; Roqué, C.; Zarroca, M.; Guerrero, J.; Sasowsky, I. Evaluation of trenching, ground penetrating radar (GPR) and electrical resistivity tomography (ERT) for sinkhole characterization. Earth Surf. Process. Landf. 2014, 39, 214–227. [CrossRef] 9. Ardestani, V.E. Detecting, delineating and modeling the connected solution cavities in a dam site via microgravity data. Acta Geod. Geophys. 2013, 48, 123–138. [CrossRef] 10. He, W.; Yu, R. Application of High-Density Resistivity Survey to Reconnaissance the Highway’s Geological Disaster in the Mountainous Area. Geotech. Investig. Surv. 2009, 37, 89–94. 11. Xue, G.; Li, X.; Di, Q. The Progress of TEM in Theory and Application. Prog. Geophys. 2007, 22, 1195–1200. 12. Milsom, J.; Eriksen, A. Ground Penetrating Radar. In Groundwater Geophysics; Wiley: Chichester, UK, 1998. 13. Al-Fares, W.; Bakalowicz, M.; Guérin, R.; Dukhan, M. Analysis of the karst aquifer structure of the Lamalou area (Hérault, France) with ground penetrating radar. J. Appl. Geophys. 2004, 51, 97–106. [CrossRef] 14. Li, S.; Li, S.; Zhang, Q.; Xue, Y.; Ding, W.; Zhong, S.; He, F.; Lin, Y. Forecast of Karst-Fractured Groundwater and Defective Geological Condition. Chin. J. Rock Mech. Eng. 2007, 26, 217–225. 15. Jiang, W. Combination of Geophysical and Conventional Boring Methods for the Investigation of an Industrial Building over Abandoned Mining Areas in Zhangqiu. Soil Eng. Found. 2017, 3, 364–368. Appl. Sci. 2019, 9, 2588 17 of 17 16. Waltham, D.T.; Bell, F.G.; Culshaw, M.G. Sinkholes and Subsidence; Springer: Berlin, Germany, 2005. 17. Yang, B.; Fang, L. Automated Extraction of 3-D Railway Tracks from Mobile Laser Scanning Point Clouds. IEEE J. Sel. Top. Appl. Earth Obs. Remote Sens. 2015, 7, 4750–4761. [CrossRef] 18. Gallay, M.; Hochmuth, Z.; Kanuk, ˇ J.; Hofierka, J. Geomorphometric analysis of cave ceiling channels mapped with 3-D terrestrial laser scanning. Hydrol. Earth Syst. Sci. 2016, 20, 1827. [CrossRef] 19. Ordóñez, C.; Cabo, C.; Sanzablanedo, E. Automatic Detection and Classification of Pole-Like Objects for Urban Cartography Using Mobile Laser Scanning Data. Sensors 2017, 17, 1465. [CrossRef] [PubMed] 20. Liu, G.; Meng, X.; Ni, J.; Chen, Z.; Zhang, D. Evaluation of the two-dimension reflection seismic method towards the exploration of thrust-controlled mineral deposits in southwestern Fujian province, China. Geophysics 2018. [CrossRef] 21. Zhong, S. Land sonar method and e ectiveness. Geophys. Geochem. Explor. 1997, 21, 172–179. 22. Guo, D.D.; Zhao, L.H.; Gao, Z.J. High-density electrical method used in the application of karst collapse. Ground Water 2011, 33, 108–110. 23. Christiansen, A.V.; Auken, E.; Sørensen, K. The transient electromagnetic method. In Groundwater Geophysics; Springer: Berlin/Heidelberg, Germany, 2006; pp. 179–226. 24. Li, X.; Xue, G.; Yin, C. Migration Imaging of the Transient Electromagnetic Method; Springer: Singapore, 2017. 25. Arifi, M.H.; Jamaluddin, T.A.; Husin, H.; Ismail, A.; Abbas, A.A.; Nordin, M.N.M.; Othman, N.A. Comparison of Geological Mapping with Electrical Resistivity and Ground Penetration Radar Methods for Rock Fractured System Study. Chiang Mai J. Sci. 2016, 43, 1346–1357. 26. Annan, A.P.; Diamanti, N.; Redman, J.D.; Jackson, S.R. Ground-penetrating radar for assessing winter roads. Geophysics 2016, 81, WA101–WA109. [CrossRef] 27. Orfanos, C.; Apostolopoulos, G. 2D–3D resistivity and microgravity measurements for the detection of an ancient tunnel in the Lavrion area, Greece. Near Surf. Geophys. 2011, 9, 449–457. [CrossRef] © 2019 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (http://creativecommons.org/licenses/by/4.0/). http://www.deepdyve.com/assets/images/DeepDyve-Logo-lg.png Applied Sciences Multidisciplinary Digital Publishing Institute

Fine Exploration and Control of Subway Crossing Karst Area

Download PDF
17 pages

Loading next page...
 
/lp/multidisciplinary-digital-publishing-institute/fine-exploration-and-control-of-subway-crossing-karst-area-Ls9eZQ7rdq

References (28)

Publisher
Multidisciplinary Digital Publishing Institute
Copyright
© 1996-2019 MDPI (Basel, Switzerland) unless otherwise stated
ISSN
2076-3417
DOI
10.3390/app9132588
Publisher site
See Article on Publisher Site

Abstract

applied sciences Article Fine Exploration and Control of Subway Crossing Karst Area Jing Wang , Liping Li *, Shaoshuai Shi * , Shangqu Sun, Xingzhi Ba and Yijie Zhang School of Qilu Transportation, Shandong University, Jinan 250061, China * Correspondence: liliping@sdu.edu.cn (L.L.); shishaoshuai@sdu.edu.cn (S.S.) Received: 13 May 2019; Accepted: 22 June 2019; Published: 26 June 2019 Featured Application: Accurate exploration and safety control of karst caves in subway construction. Abstract: A large number of subway projects need to cross all kinds of disaster sources during the construction process. When a disaster source is unknown and uncertain, it is dicult for tunnel stability analysis to conform to the actual situation, which is likely to cause serious geological disasters. Firstly, the accurate location of the source of the disaster is realized via the geophysical method, and the orientation of the target is determined. Secondly, real imaging of the geological disaster source is realized using fine three-dimensional scanning equipment. Finally, the coupling law of the seepage field, displacement field, and stress field of the tunnel surrounding rock are analyzed. The stability of the tunnel is analyzed, and the reasonable karst treatment method is put forward. Keywords: disaster source; geophysical method; orientation of the target; reasonable karst treatment method 1. Introduction The distribution area of karst in China is 3.65 million square kilometers, accounting for more than one-third of the territory. Karst is most developed in the Southern provinces of Guizhou, Hunan, Jiangxi, Sichuan, Yunnan, and Hubei, and in the Northern provinces of Hebei, Shandong, and Liaoning. Additionally, many karst development areas are distributed in metro construction cities, such as Jinan Metro, which needs to pass through hard rock water-rich caves [1], Wuhan Metro, which needs to pass through “honeycomb caves”, Changsha Metro, which needs to pass through complex underwater caves, and so on. In the soluble strata, limestone may contain limestone fragments and fissures locally (Figure 1). The existence of limestone fissures provides water storage conditions and transportation channels for groundwater [2]. Caves of di erent sizes, shapes, and buried depths are formed due to the dissolution and erosion of groundwater [3]. If these caves are not accurately identified, the following risks are likely to occur: 1. Shield machine pitch, jamming or water inrush (Figure 2); 2. Karst cave collapse above the tunnel leading to the surface collapse; 3. During the operation period, vehicle vibration causing surface collapse or karst cave collapse under the segment, which leads to risks in train operation; 4. The existence of karst water leading to the continuous development of karst caves, which threatens the long-term operation of the metro. Appl. Sci. 2019, 9, 2588; doi:10.3390/app9132588 www.mdpi.com/journal/applsci Appl. Sci. 2019, 9, x 2 of 17 Appl. Sci. 2019, 9, 2588 2 of 17 Appl. Sci. 2019, 9, x 2 of 17 (a) (b) Figure 1. Dissolution limestone and limestone fragments. (a) dissolution limestone; (b) limestone (a) (b) fragments. Figure Figure 1. 1. D Dis isso so lulu tition lim on limeste osnto ene and l and limesitm oneesto frange frag mentsm . (e ants. ) diss(o al) di utiosso n lilu mtion lim estone; (best ) lio m ne; ( estob ne ) lim fragest meo nne ts. fragments. (a) (b) Figure 2. Figure 2. Wate Water r inru inrush sh from from s shield hield tunnel. tunnel. ( (a a) front of the ) front of the tunnel; ( tunnel; (b b) ) inside inside the tunnel. the tunnel. (a) (b) In the aspect of karst detection, a large number of geophysical methods (including electrical, In the aspect of karst detection, a large number of geophysical methods (including electrical, Figure 2. Water inrush from shield tunnel. (a) front of the tunnel; (b) inside the tunnel. electromagnetic, elastic wave, and microgravity) have emerged [4–13]. However, the geological electromagnetic, elastic wave, and microgravity) have emerged [4–13]. However, the geological conditions In the a insthe pect of karst ka ar rst detecti ea are complex, on, a la and rge number it is di of geophysic cult to accurately al minvestigate ethods (incthe luding electric underground al, conditions in the karst area are complex, and it is difficult to accurately investigate the underground conditions by a single geophysical method [14,15]. With the advancement of geophysical methods and electromagnetic, elastic wave, and microgravity) have emerged [4–13]. However, the geological conditions by a single geophysical method [14,15]. With the advancement of geophysical methods interpr conditions etation in ttechniques, he karst are gr a eat are achievements complex, and it have is di been fficmade ult to in acc karst urate exploration ly investigat [16 e t ].hMor e underg e successful round and interpretation techniques, great achievements have been made in karst exploration [16]. More detection cases demonstrate that comprehensive detection method can e ectively reduce the uncertainty conditions by a single geophysical method [14,15]. With the advancement of geophysical methods successful detection cases demonstrate that comprehensive detection method can effectively reduce and and interpret reduce the ation error techniques, g interpretation reat results achievements when exploring have been the under made in karst explora ground karst structur tion [16 e. Ho ]. Mor wever e, the uncertainty and reduce the error interpretation results when exploring the underground karst geophysical prospecting methods can only locate karst caves, which is dicult to quantify. Borehole successful detection cases demonstrate that comprehensive detection method can effectively reduce structure. However, geophysical prospecting methods can only locate karst caves, which is difficult laser the uncertain scanningty and red technology ucis e the error in a method toterpretati get the point on recloud sults when data of exploring the three-dimensional the undergroun surface d karof st to quantify. Borehole laser scanning technology is a method to get the point cloud data of the three- the inner wall of the cavity by extending the probe with integrated laser scanning function into the structure. However, geophysical prospecting methods can only locate karst caves, which is difficult dimensional surface of the inner wall of the cavity by extending the probe with integrated laser cavity to qua.nIts tify. Borehol principle is e la the ser sca same nni asng that technol of theostanding gy is a method to get the poi laser scanner, but its ng t cl reatest oud da advantage ta of the three- is the scanning function into the cavity. Its principle is the same as that of the standing laser scanner, but miniaturization of the laser probe, which can adapt to various narrow channels and space and get data dimensional surface of the inner wall of the cavity by extending the probe with integrated laser its greatest advantage is the miniaturization of the laser probe, which can adapt to various narrow deep scanni into ng functi the rock on i mass nto the ca [17,18vi ]. ty. Its pri At present, ncidrilling ple is the laser same technology as that of is the sta mainly nding l used in aser sca the goaf nner, but of coal channels and space and get data deep into the rock mass [17,18]. At present, drilling laser technology mine, but it is not combined with geophysical prospecting methods, which leads to the problem of its greatest advantage is the miniaturization of the laser probe, which can adapt to various narrow is mainly used in the goaf of coal mine, but it is not combined with geophysical prospecting methods, blind channel drilling. s and sp Ther ace efor and get e, this dat paper a deep synthetically into the rock determines mass [17,18the ]. At karst present development , drilling laar ser ea teby chn means ology which leads to the problem of blind drilling. Therefore, this paper synthetically determines the karst of various geophysical prospecting. Targeted drilling and quantitative exploration of karst cave by is mainly used in the goaf of coal mine, but it is not combined with geophysical prospecting methods, development area by means of various geophysical prospecting. Targeted drilling and quantitative drilling which lelaser ads to ar tehcarried e proble out. m of blind drilling. Therefore, this paper synthetically determines the karst exploration of karst cave by drilling laser are carried out. development area by means of various geophysical prospecting. Targeted drilling and quantitative 2 explorat . Quanti ionta oti f k ve a rstEx cplorati ave byo drn Met illing lh aod ser arof Ka e carrirst ed out Cave Ba . sed on Three-Dimensional Laser Measurement 2. Quantitative Exploration Method of Karst Cave Based on Three-Dimensional Laser Measurement Appl. Sci. 2019, 9, 2588 3 of 17 Appl. Sci. 2019, 9, x 3 of 17 2. Quantitative Exploration Method of Karst Cave Based on Three-Dimensional Laser Measurement 2.1. 3-D Automatic Laser Scanning Technology 2.1. 3-D Automatic Laser Scanning Technology Three-dimensional automatic laser scanning technology uses laser diodes to emit laser pulses. Three-dimensional automatic laser scanning technology uses laser diodes to emit laser pulses. Laser pulses propagate to the target point under testing [19]. The photosensitive secondary tube Laser pulses propagate to the target point under testing [19]. The photosensitive secondary tube receives laser signals reflected from the surface of the object. The “flight time” of the laser is receives laser signals reflected from the surface of the object. The “flight time” of the laser is calculated. calculated. The distance L between the scanner and the target point under testing is calculated by the The distance L between the scanner and the target point under testing is calculated by the speed of speed of light C and the “flight time” Δt. A precision clock control encoder synchronously measures light C and the “flight time” Dt. A precision clock control encoder synchronously measures transverse transverse scanning angle observation value alpha and longitudinal scanning angle observation scanning angle observation value alpha and longitudinal scanning angle observation value beta of value beta of each laser pulse. Laser scanning three-dimensional measurement uses the internal each laser pulse. Laser scanning three-dimensional measurement uses the internal coordinate system coordinate system of the instrument. The X-axis is in the transverse scanning plane, the Y-axis is of the instrument. The X-axis is in the transverse scanning plane, the Y-axis is perpendicular to the perpendicular to the X-axis in the transverse scanning plane, and the Z-axis is perpendicular to the X-axis in the transverse scanning plane, and the Z-axis is perpendicular to the transverse scanning transverse scanning plane (Figure 3). The formula for calculating the coordinates of three- plane (Figure 3). The formula for calculating the coordinates of three-dimensional laser foot points can dimensional laser foot points can be obtained as follows: be obtained as follows: L = cDt (1) (1) 𝐿 𝑐∆𝑡 8 9 8 > x > > L cos cos > > > > > > 𝐿cos𝛽cos𝛼 < = < y = L cos sin (2) > > > > >𝑦 > 𝐿cos𝛽sin𝛼 (2) > > > : ; : z L sin 𝐿sin𝛽 In the formula, C is the propagation speed of the laser in the atmosphere, Dt is the round-trip In the formula, 𝐶 is the propagation speed of the laser in the atmosphere, ∆𝑡 is the round-trip propagation time of the laser at the distance to be measured, is the observation value of the transverse propagation time of the laser at the distance to be measured, 𝛼 is the observation value of the scanning angle, and is the observation value of the longitudinal scanning angle. transverse scanning angle, and 𝛽 is the observation value of the longitudinal scanning angle. (a) (b) Figure 3. Schema of propagation time ranging method and internal coordinate system of laser Figure 3. Schema of propagation time ranging method and internal coordinate system of laser detector. ( detector a) schema . (aof ) schema of propagation time ranging method; propagation time ranging method; (b) the internal (b) the coor internal dinatecoordinate system of syst laser em of detector laser . detector. The automatic laser scanning system of the empty area is mainly divided into horizontal scanning mode and vertical scanning mode. The automatic laser scanning system of the empty area is mainly divided into horizontal scanning mode and vertical scanning mode. Horizontal scanning mode: The most commonly used scanning mode. First, the scanning head • Horizontal scanning mode: The most commonly used scanning mode. First, the scanning head rotates vertically to the position of vertical angle 0 (the upper part of the detector is straight) rotates vertically to the position of vertical angle 0° (the upper part of the detector is straight) and begins the first round of complete 360 horizontal scanning. After each circle of horizontal and begins the first round of complete 360° horizontal scanning. After each circle of horizontal scanning, the scanning head increases the increment of steps set by the user along the vertical scanning, the scanning head increases the increment of steps set by the user along the vertical direction and starts the next circle of horizontal scanning until the vertical axis rotates 180 in direction and starts the next circle of horizontal scanning until the vertical axis rotates 180° in the vertical direction. During the last horizontal scan of the scanner head, the laser emission and the vertical direction. During the last horizontal scan of the scanner head, the laser emission and receiving lens of the scanner head point in front of the detector (Figure 4). receiving lens of the scanner head point in front of the detector (Figure 4). Vertical scanning mode: Vertical scanning is suitable for scanning under some special conditions. • Vertical scanning mode: Vertical scanning is suitable for scanning under some special Especially, the scanning line obtained is perpendicular to the horizontal characteristics of the conditions. Especially, the scanning line obtained is perpendicular to the horizontal scanning object so that more details that are comprehensive can be captured. As shown in the characteristics of the scanning object so that more details that are comprehensive can be figure, in the vertical scanning process, the scanning head first rotates from vertical angle position captured. As shown in the figure, in the vertical scanning process, the scanning head first rotates 0 (the vertical direction behind the detector) to vertical angle position 180 (the laser-transmitting from vertical angle position 0 (the vertical direction behind the detector) to vertical angle and -receiving lens of the scanning head points in front of the detector) along the vertical direction position 180° (the laser-transmitting and -receiving lens of the scanning head points in front of the detector) along the vertical direction and completes the first vertical scanning. After each vertical scan, the scanning head increases a user-set increment along the horizontal direction Appl. Sci. 2019, 9, 2588 4 of 17 Appl. Appl. Sci. Sci. 2019 2019, , 9 9, x , x 4 of 4 of 17 17 and completes the first vertical scanning. After each vertical scan, the scanning head increases a user-set increment along the horizontal direction and starts the next vertical scan until the and starts the next vertical scan until the horizontal axis rotates 360 degrees in the horizontal and starts the next vertical scan until the horizontal axis rotates 360 degrees in the horizontal horizontal axis rotates 360 degrees in the horizontal direction (Figure 5). direct direction ion (F (Fig igure ure 5) 5).. Figure 4. Figure 4. Horizontal scanning mode. Horizontal scanning mode. Figure 4. Horizontal scanning mode. Figure 5. Vertical scanning mode. Figure 5. Vertical scanning mode. Figure 5. Vertical scanning mode. 2.2. Data Processing of Laser Point Cloud 2.2. Data Processing of Laser Point Cloud 2.2. Data Processing of Laser Point Cloud Aft Afte er r obt obta ain ini in ng t g th he o e or rig igin ina al l point point clo clou ud d dat data a vi via a a lase a laser three-dimen r three-dimens sion iona al measur l measurement sy ement system, stem, After obtaining the original point cloud data via a laser three-dimensional measurement system, it is necessary to filter, stitch, and model the original point cloud data. Specifically, as follows: it is necessary to filter, stitch, and model the original point cloud data. Specifically, as follows: it is necessary to filter, stitch, and model the original point cloud data. Specifically, as follows: Data Data filterin filtering g:: Due to the Due to the influence o influence of f e ex xternal ternal envir enviro onmental nmental factors factors and the and the uneven re uneven reflection flection Data filtering: Due to the influence of external environmental factors and the uneven reflection characteristics of the empty area wall during the scanning process, the final scanned point cloud data characteristics of the empty area wall during the scanning process, the final scanned point cloud data characteristics of the empty area wall during the scanning process, the final scanned point cloud contain no contain no distance po distance points and bad points. At th ints and bad points. At the same e same time, time, the rapid the rapid oper operation ation of a laser of a laser range range data contain no distance points and bad points. At the same time, the rapid operation of a laser finder during scanning will also lead to the phenomenon of an “intermediate medium point” in finder during scanning will also lead to the phenomenon of an “intermediate medium point” in range finder during scanning will also lead to the phenomenon of an “intermediate medium point” in dif diff ferent erent pha phas ses of t es of th he e la lase ser beam, re r beam, resu sult lting in po ing in point int displ displa acement cement. . For t For th his re is reaso ason n, point , point clou cloud dat d data a di erent phases of the laser beam, resulting in point displacement. For this reason, point cloud data are processed by filtering out single obvious bad points in scanning. are processed by filtering out single obvious bad points in scanning. are processed by filtering out single obvious bad points in scanning. Fi Firstly, rstly, a accordi ccordin ng to the fixed spa g to the fixed spac ce e ra range of nge of th the worki e workin ng g a ar rea ea, the poi , the poin nt beyond thi t beyond this s ra range ca nge can n Firstly, according to the fixed space range of the working area, the point beyond this range can be be considered as noise point filtering. Secondly, on the same scanning plane, if the distance between be considered as noise point filtering. Secondly, on the same scanning plane, if the distance between considered as noise point filtering. Secondly, on the same scanning plane, if the distance between a a point a point and and it its adj s adja acent cent t tw wo point o points s exce exceeds a ce eds a cert rtain t ain tr rust uste ed va d valu lue, e, t th he point e point is consider is considered di ed dis st tort ortiion on point and its adjacent two points exceeds a certain trusted value, the point is considered distortion point filtering. However, considering the point of edge, because it is far from the scanning center, the point filtering. However, considering the point of edge, because it is far from the scanning center, the point filtering. However, considering the point of edge, because it is far from the scanning center, d diis st tan anc ce e b be et tw we ee en n s sa am mp plliin ng g p po oiin nt ts s i is s v ve er ry y lla ar rg ge e.. At At this ti this time, the a me, the an ngl gle between t e between th he combi e combin niin ng poi g poin nt t the distance between sampling points is very large. At this time, the angle between the combining and the front and back points on the scanning line is considered as a distortion point if the angle and the front and back points on the scanning line is considered as a distortion point if the angle point and the front and back points on the scanning line is considered as a distortion point if the angle bet betw ween t een th hem is em is les less s t th han an a c a ce ert rta aiin con n conf fidenc idence e va valu lue e (F (Figu igur re e 6) 6).. between them is less than a certain confidence value (Figure 6). Appl. Sci. 2019, 9, 2588 5 of 17 Appl. Sci. 2019, 9, x 5 of 17 Appl. Sci. 2019, 9, x 5 of 17 Figure 6. Distortion points on scanning line. Figure 6. Distortion points on scanning line. Figure 6. Distortion points on scanning line. Data mosaic: Because the laser travels along a straight line, some areas will not be detected Data mosaic: Because the laser travels along a straight line, some areas will not be detected accurately if occlusion or obstruction occurs during the scanning process. Therefore, in order to detect accurately if occlusion or obstruction occurs during the scanning process. Therefore, in order to detect Data mosaic: Because the laser travels along a straight line, some areas will not be detected the actual boundary of the airspace as accurately as possible, it is very important to select a reasonable the act accurately ual bounda if occlusion ry of the or ob airsstruct pace a ion s ac occ curat urs during ely as p th oe sc ssib annin le, itg i pr s ver ocess. There y importf ant ore, to in o sel rder ect to detect a reasonable detection location. For the complex shape of the empty area, we should try to carry out multi-point the actual boundary of the airspace as accurately as possible, it is very important to select a reasonable detection location. For the complex shape of the empty area, we should try to carry out multi-point detection and then splice the point data obtained by multiple detection scans to form an area completely detection location. For the complex shape of the empty area, we should try to carry out multi-point detection and then splice the point data obtained by multiple detection scans to form an area void of detection an point cloud d then sp data. lice The the point d essence ofathe ta obt data ained mosaic by mu islt to iplcompute e detection thescrans t otation o form and an translation area completely void of point cloud data. The essence of the data mosaic is to compute the rotation and completely void of point cloud data. The essence of the data mosaic is to compute the rotation and transformation matrix R, T, which satisfies the following objective functions: translation transformation matrix 𝑅 , 𝑇 , which satisfies the following objective functions: translation transformation matrix 𝑅 , 𝑇 , which satisfies the following objective functions: ( ) [ ] f𝑓 R 𝑅,,𝑇 T =m min in R𝑅∙𝑝p +𝑇T𝑞 q (3 (3) ) i i 𝑓 𝑅,𝑇 min 𝑅∙𝑝 𝑇𝑞 (3) where, 𝑝 and 𝑞 are point clouds that need to be aligned, and the upper formula is a highly where, p and q are point clouds that need to be aligned, and the upper formula is a highly nonlinear where, i 𝑝 and i 𝑞 are point clouds that need to be aligned, and the upper formula is a highly nonlinear problem. The research of the data mosaic focuses on finding a fast and effective solution to problem. nonline The ar pro resear blem. The ch of the res data earch mosaic of the d focuses ata mosa on ic finding focuses on a fast findi and ng a e fective ast andsolution effective so to this lution t problem. o this problem this problem . . Because the point coordinates of the point cloud data obtained by each scan are relative to the Because the point coordinates of the point cloud data obtained by each scan are relative to the Because the point coordinates of the point cloud data obtained by each scan are relative to the coordinate system of the scan, the three-dimensional coordinates of the points obtained by di erent coordinate system of the scan, the three-dimensional coordinates of the points obtained by different coordinate system of the scan, the three-dimensional coordinates of the points obtained by different scanning times (di erent locations or angles of view) are in di erent coordinate systems. Therefore, scanning times (different locations or angles of view) are in different coordinate systems. Therefore, scanning times (different locations or angles of view) are in different coordinate systems. Therefore, we must try to put the three-dimensional point cloud data acquired by multiple scans into a common we must try to put the three-dimensional point cloud data acquired by multiple scans into a common we must try to put the three-dimensional point cloud data acquired by multiple scans into a common coordinate system, to obtain the complete three-dimensional point data in the empty space. This process coordinate system, to obtain the complete three-dimensional point data in the empty space. This coordinate system, to obtain the complete three-dimensional point data in the empty space. This is called a multi-point scanning data mosaic. The principle is shown in Figure 7. process is called a multi-point scanning data mosaic. The principle is shown in Figure 7. process is called a multi-point scanning data mosaic. The principle is shown in Figure 7. Figure 7. Mosaic of multi-point scanning data. Figure 7. Mosaic of multi-point scanning data. Specific cases are as follows: Boreholes #1 and #2 are selected to detect a karst cave twice, and Specific cases are as follows: Boreholes #1 and #2 are selected to detect a karst cave twice, and the Figure 7. Mosaic of multi-point scanning data. the original point clouds detected by two boreholes are obtained through detection. The original original point clouds detected by two boreholes are obtained through detection. The original point point cloud data of borehole #1 are filtered as shown in Figure 8a, and those of borehole #2 are filtered cloud data of borehole #1 are filtered as shown in Figure 8a, and those of borehole #2 are filtered as Specific cases are as follows: Boreholes #1 and #2 are selected to detect a karst cave twice, and as shown in Figure 8b. In each detection process, the borehole coordinates and initial azimuth angle shown in Figure 8b. In each detection process, the borehole coordinates and initial azimuth angle are the original point clouds detected by two boreholes are obtained through detection. The original are recorded. In the process below the probe, the system software automatically records the changes recorded. In the process below the probe, the system software automatically records the changes of point cloud d of depth, aazimuth, an ta of borehole #1 d dip ang are filter le belo ew and d as show then sp n inlices the tw Figure 8a, an o detected d d those of bor ata ine the so hole #ftware to 2 are filtered depth, azimuth, and dip angle below and then splices the two detected data in the software to make make the same detection point position coincide completely. The 3-D point cloud model of the karst as shown in Figure 8b. In each detection process, the borehole coordinates and initial azimuth angle the same detection point position coincide completely. The 3-D point cloud model of the karst cave are recorded. In the process below the probe, the system software automatically records the changes formed by the splicing of boreholes #1 and #2 are shown in Figure 8c,d. The “point cloud creating of depth, azimuth, and dip angle below and then splices the two detected data in the software to make the same detection point position coincide completely. The 3-D point cloud model of the karst Appl. Sci. 2019, 9, 2588 6 of 17 Appl. Sci. 2019, 9, x 6 of 17 cave formed by the splicing of boreholes #1 and #2 are shown in Figure 8c,d. The “point cloud creating entity” of “entity modeling” is used to automatically construct the three-dimensional figure contour of entity” of "entity modeling" is used to automatically construct the three-dimensional figure contour the cave and generate the three-dimensional entity model of the cave (Figure 8). of the cave and generate the three-dimensional entity model of the cave (Figure 8). (a) (b) (c) (d) (e) (f) Figure 8. Construction of three-dimensional real model of karst cave. (a) Primitive point cloud Figure 8. Construction of three-dimensional real model of karst cave. (a) Primitive point cloud of of borehole #1; (b) Primitive point cloud of borehole #2; (c) Point cloud after splicing borehole #1; borehole #1; (b) Primitive point cloud of borehole #2; (c) Point cloud after splicing borehole #1; (d) (d) Point cloud after splicing borehole #2; (e) Point cloud model after splicing boreholes #1 and #2; Point cloud after splicing borehole #2; (e) Point cloud model after splicing boreholes #1 and #2; (f) (f) Three-dimensional solid model of karst cave. Three-dimensional solid model of karst cave. Appl. Sci. 2019, 9, x 7 of 17 Appl. Sci. 2019, 9, 2588 7 of 17 3. General Situation of Engineering Geology and Location and Quantitative Exploration Method 3. General Situation of Engineering Geology and Location and Quantitative Exploration Method of Jinan Metro’s Karst Cave of Jinan Metro’s Karst Cave Traffic congestion in Jinan ranks first in the country all year round, and it is urgent to build the Trac congestion in Jinan ranks first in the country all year round, and it is urgent to build the subway. Jinan Metro proposed the planning of the urban core area express line (R line) and the central subway. Jinan Metro proposed the planning of the urban core area express line (R line) and the central city general line (M line). The express line consists of three lines: R1, R2, and R3. The central city’s city general line (M line). The express line consists of three lines: R1, R2, and R3. The central city’s general line includes 7 lines, the loop line and the M1 to M6 lines, forming a "loop + radiation" line general line includes 7 lines, the loop line and the M1 to M6 lines, forming a “loop + radiation” line network structure. In 2015, the R1 line of the first line of Jinan Metro officially started. Since then, network structure. In 2015, the R1 line of the first line of Jinan Metro ocially started. Since then, three lines in total have been started. three lines in total have been started. Jinan is also famous for its spring water. The origin of the spring water is mainly due to the Jinan is also famous for its spring water. The origin of the spring water is mainly due to the barrier of the northern impermeable magmatic rock in the process of the northward runoff of karst barrier of the northern impermeable magmatic rock in the process of the northward runo of karst water, and then the groundwater flows out in the limestone sky window under the large pressure of water, and then the groundwater flows out in the limestone sky window under the large pressure of the water head. Therefore, the construction of Jinan Metro needs to pass through a large number of the water head. Therefore, the construction of Jinan Metro needs to pass through a large number of limestone formations with strong karst development. In order to ensure the rapid and safe limestone formations with strong karst development. In order to ensure the rapid and safe construction construction of the subway, it is very necessary to carry out meticulous exploration and treatment of of the subway, it is very necessary to carry out meticulous exploration and treatment of karst caves in karst caves in karst areas. karst areas. 3.1. General Situation of Engineering Geology 3.1. General Situation of Engineering Geology The length of the Wangfu village station to the Dayang village station on the R1 line of Jinan The length of the Wangfu village station to the Dayang village station on the R1 line of Jinan Metro Metro is about 2033 m. This subway section passes through the middle weathered-limestone is about 2033 m. This subway section passes through the middle weathered-limestone development development area. The length of the left line tunnel through limestone is about 725 m, and the length area. The length of the left line tunnel through limestone is about 725 m, and the length of the right of the right line tunnel is about 798 m. Preliminary investigation data show that the uniaxial line tunnel is about 798 m. Preliminary investigation data show that the uniaxial compressive strength compressive strength of moderately weathered limestone is 34.2–83.2 Mpa. The geological boreholes of moderately weathered limestone is 34.2–83.2 Mpa. The geological boreholes along the tunnel reveal along the tunnel reveal karst caves in the middle weathered-limestone section. The main source of karst caves in the middle weathered-limestone section. The main source of groundwater is limestone groundwater is limestone fracture karst water, which is the largest water area in the central and fracture karst water, which is the largest water area in the central and western parts of Jinan. The section western parts of Jinan. The section is a rich water area, where the water supply is large, and the is a rich water area, where the water supply is large, and the groundwater is confined (Figure 9). groundwater is confined (Figure 9). Figure 9. Geologic profile of the distance between the Wangfu village station and the Dayang Figure 9. Geologic profile of the distance between the Wangfu village station and the Dayang village village station. station. The hydrogeological map shows that the interval through the weathered-limestone section is the The hydrogeological map shows that the interval through the weathered-limestone section is largest water area in the central and western part of Jinan. The output of a single well of fractured the largest water area in the central and western part of Jinan. The output of a single well of fractured karst water is more than 10,000 m /d, which indicates that this section is a water-rich area with large karst water is more than 10,000 m /d, which indicates that this section is a water-rich area with large water recharge and confined groundwater (Figure 10). The figure below shows one of the exposed water recharge and confined groundwater (Figure 10). The figure below shows one of the exposed karst caves (Figure 11). karst caves (Figure 11). Appl. Sci. 2019, 9, 2588 8 of 17 Appl. Sci. 2019, 9, x 8 of 17 Appl. Sci. 2019, 9, x 8 of 17 Figure 10. Figure 10. G Ge eo ollogic profil ogic profile of e of t th he dis e dist tance bet ance betw ween the een the Wangfu Wangfu village village stati statio on and the Day n and the Daya ang village ng village Figure 10. Geologic profile of the distance between the Wangfu village station and the Dayang station. station. village station. Figure 11. Exposed water-bearing karst cave. Figure 11. Exposed water-bearing karst cave. Figure 11. Exposed water-bearing karst cave. 3.2. Location Exploration Method of Karst Cave 3. 3.2. 2. Locati Location on E Expl xplora orat tiio on n Met Meth hod od of of K Ka arst rst C Ca ave ve Table 1 mainly introduces six common geophysical methods under di erent detection principles. Ta Table ble 11 mainly introduces six mainly introduces six common geop common geophy hysic sicaal method l methods under s under different detection different detection Each of them has di erent characteristics. principles. Each of them h principles. Each of them ha as different ch s different char aracterist acteristics. ics. In accordance with the characteristics of geophysical prospecting and the engineering geology of the R1 line, the most suitable geophysical method was selected. First, the subway was built in the urban Table 1. Table 1. The The characteristi characteristic cs s of of different g different ge eop ophy hysical m sical me ethod thods. s. area, where the surface soil is thicker. The seismic wave reflection method and the ground-penetrating Prediction met Prediction meth hod od Characteristic Characteristic radar method lead to more disturbances. Therefore, these two methods are not applicable. Second, The dete The detection a ction accuracy is ccuracy is higher in the range higher in the range of 20–200 mete of 20–200 meters and the rs and the dete detection ction The seismic wa The seismic wave ve because of the abundance of groundwater in the interval, the microgravity method is not applicable. effect effect is is better f better fo or karst cav r karst cave es. s. However, However, the a the ad daptability aptability to t to th hick overbu ick overburde rden n soil soil reflection reflection method [20] method [20] Third, the upper part of the subway line is a highway, and the high-density electrical method leads is poor is poor, and , and en energy attenu ergy attenuation is ation is faster. faster. to certain destructiveness on the road surface. Finally, the transient electromagnetic method is more The land The land sonar method sonar method The predict The predictiion on of medium and of medium and small small cav cave ern rns s and fractu and fractured z red zo ones i nes is s eff effe ecti ctiv ve, bu e, but t suitable for the comparison between the land sonar method and the transient electromagnetic method. [21] [21] the velo the velocity city of of each lay each laye er r ca cannot be accurately obtained. nnot be accurately obtained. No filling cavern or water-rich cavern with the obvious electrical difference with The principle of the transient No fi electr lling omagnetic cavern or water-ric method h cavern with is that a pulsed the obviou magnetic s elec field trical is differenc transmitted e with to The high-density The high-density su surrou rroun nding ding rock rock stratu stratum m is is g good. ood. It It can onl can only y be qu be qualitat alitative ive bu but not t not the front of the working face using an ungrounded line. When the current in the transmission line electrical method [22] electrical method [22] quantitatively explored. quantitatively explored. is abruptly disconnected, the two eddy fields will be excited to maintain the magnetic field (that is, It is sensitive to large water-filled low-resistivity zones and has the ability to It is sensitive to large water-filled low-resistivity zones and has the ability to one field) before the disconnected current, the size, and attenuation of the two eddy current field The transient The transient penetrate low-resistance coverage. The depth of detection is large. However, the penetrate low-resistance coverage. The depth of detection is large. However, the and the electricity of the surrounding medium. This is related to the electrical distribution of the electromagnetic method electromagnetic method resolu resolution of tion of e em mpty caves or pty caves or dry-filling kars dry-filling karst cave t caves s is is not e not en nou ough, so it gh, so it is is diffi difficu cult lt surrounding [23,24] [23,24] medium. The variation of the secondary field with time is observed during the first to di to distingu stinguish. ish. field intermittence. After processing, the electric property, the scale, and the form of the underground In the high-resistivity area, the detection depth is 20–30 meters and the detection In the high-resistivity area, the detection depth is 20–30 meters and the detection The ground-penetrating The ground-penetrating medium can be understood to achieve the aim of detecting the target. effect is good for karst caves and faults. However, it is easy to be affected by the effect is good for karst caves and faults. However, it is easy to be affected by the radar method [ radar method [25,26] 25,26] su surface so rface soil il, an , and the d the detec detecttion ion depth i depth is s g gr reatl eatly y redu reduced. ced. Under flat terrain, it is widely used in karst investigation. However, factors such Under flat terrain, it is widely used in karst investigation. However, factors such The microgravity The microgravity as topography fluctuation, sediment thickness, and fluctuation of diving surface as topography fluctuation, sediment thickness, and fluctuation of diving surface method [27] method [27] are relative are relatively l ly la arge. rge. Appl. Sci. 2019, 9, 2588 9 of 17 Table 1. The characteristics of di erent geophysical methods. Prediction Method Characteristic The detection accuracy is higher in the range of 20–200 m and the The seismic wave reflection detection e ect is better for karst caves. However, the adaptability to thick method [20] overburden soil is poor, and energy attenuation is faster. The prediction of medium and small caverns and fractured zones is The land sonar method [21] e ective, but the velocity of each layer cannot be accurately obtained. No filling cavern or water-rich cavern with the obvious electrical The high-density electrical di erence with surrounding rock stratum is good. It can only be method [22] qualitative but not quantitatively explored. It is sensitive to large water-filled low-resistivity zones and has the ability The transient electromagnetic to penetrate low-resistance coverage. The depth of detection is large. method [23,24] However, the resolution of empty caves or dry-filling karst caves is not enough, so it is dicult to distinguish. In the high-resistivity area, the detection depth is 20–30 m and the The ground-penetrating radar detection e ect is good for karst caves and faults. However, it is easy to be method [25,26] a ected by the surface soil, and the detection depth is greatly reduced. Under flat terrain, it is widely used in karst investigation. However, The microgravity method [27] factors such as topography fluctuation, sediment thickness, and fluctuation of diving surface are relatively large. The main reason for choosing high-density resistivity method and transient electromagnetic method for comprehensive detection is that the resistivity of underground rock is mainly influenced by mineral composition, water content, and temperature of rock. These complex factors result in the instability of rock resistivity and change in a large range. When there are fissures or fault zones in underground rocks and water-rich rocks with water-conducting channels, the resistivity of natural rocks located in these structural areas will be significantly reduced. There are obvious electrical di erences with surrounding strata. Previous geological survey and site exposure show that it has the geological and physical basis of electrical detection. Each geophysical prospecting method has its own advantages and disadvantages. It is often dicult to satisfy the requirement of detection accuracy by using a single method. The combination of various geophysical methods can complement each other and verify each other. We have made a total of 500 meters of detection, from L30+900–L31+450. Figure 12b transient electromagnetic (TEM) locations are from L30+900–L31+40 and L31+110–L31+290, totaling 500 m. Five sets of high-density resistivity have been made, each of which is 100 m. Figure 12a shows the third group, which is from L31+150–L31+250. By means of resistivity anomaly, areas with strong karst development are detected. In these areas, we determined the locations of five boreholes, h1(110), h2 (230), h3 (280), h4 (315), and h5 (350) in Figure 12b, respectively. From the results of core drilling, it can be seen that all five boreholes encounter karst caves. Appl. Sci. 2019, 9, x 10 of 17 Appl. Sci. 2019, 9, x 10 of 17 Appl. Sci. 2019, 9, 2588 10 of 17 (a) (a) (b) (b) Figure 12. Comprehensive interpretation diagram of the high-density resistivity method and transient Figure 12. Comprehensive interpretation diagram of the high-density resistivity method and transient Figure 12. Comprehensive interpretation diagram of the high-density resistivity method and transient electromagnetic. (a) The result of high-density resistivity method; (b) The result of transient electromagnetic. (a) The result of high-density resistivity method; (b) The result of transient electromagnetic. (a) The result of high-density resistivity method; (b) The result of transient electromagnetic. electromagnetic. electromagnetic. The core of each drill is shown in Figure 13. The core of each drill is shown in Figure 13. The core of each drill is shown in Figure 13. (a) (b) (a) (b) (c) (d) (c) (d) Figure 13. Drilling core drawing. (a) Coring of hole h1; (b) Coring of hole h2; (c) Coring of hole h3; Figure 13. Drilling core drawing. (a) Coring of hole h1; (b) Coring of hole h2; (c) Coring of hole h3; Figure 13. Drilling core drawing. (a) Coring of hole h1; (b) Coring of hole h2; (c) Coring of hole h3; (d) Coring of hole h4; (e) Coring of hole h5. (d) Coring of hole h4; (e) Coring of hole h5. (d) Coring of hole h4; (e) Coring of hole h5. Appl. Sci. 2019, 9, x 11 of 17 Appl. Sci. 2019, 9, 2588 11 of 17 Appl. Sci. 2019, 9, x 11 of 17 Using five target drilling points, through the improvement of exploration equipment and Using five target drilling points, through the improvement of exploration equipment and exploration method, using panoramic probe sampling, combined with automatic ray compensation Using five target drilling points, through the improvement of exploration equipment and exploration method, using panoramic probe sampling, combined with automatic ray compensation and automatic positioning technology, the acquisition of geological images in a borehole dark exploration method, using panoramic probe sampling, combined with automatic ray compensation and and automatic positioning technology, the acquisition of geological images in a borehole dark environment was achieved. Long distance accurate detection and real imaging of disaster sources automatic positioning technology, the acquisition of geological images in a borehole dark environment environment was achieved. Long distance accurate detection and real imaging of disaster sources such as karst cave were realized by 3D laser scanning (MDL, Edinburgh, Scotland). was achieved. Long distance accurate detection and real imaging of disaster sources such as karst cave such as karst cave were realized by 3D laser scanning (MDL, Edinburgh, Scotland). The characteristics of 3D laser scanning (Figure 14) are as follows: (1) Rapidity: The spatial were realized by 3D laser scanning (MDL, Edinburgh, Scotland). The characteristics of 3D laser scanning (Figure 14) are as follows: (1) Rapidity: The spatial information of the karst cave can be obtained quickly, and the coordinate information of the karst The characteristics of 3D laser scanning (Figure 14) are as follows: (1) Rapidity: The spatial information of the karst cave can be obtained quickly, and the coordinate information of the karst cave surface can be measured in time. (2) Non-contact: We can scan the targets in a non-contact way. information of the karst cave can be obtained quickly, and the coordinate information of the karst cave surface can be measured in time. (2) Non-contact: We can scan the targets in a non-contact way. (3) Penetration: Under the water cut condition of the cave, it can cross the water body and reach the cave surface can be measured in time. (2) Non-contact: We can scan the targets in a non-contact way. (3) Penetration: Under the water cut condition of the cave, it can cross the water body and reach the target surface. (4) Real-time, dynamic, and active: The target information is obtained by the reflection (3) Penetration: Under the water cut condition of the cave, it can cross the water body and reach the target surface. (4) Real-time, dynamic, and active: The target information is obtained by the reflection of light emitted by itself. It cannot be constrained by time and space, and the beam is quasi-parallel target surface. (4) Real-time, dynamic, and active: The target information is obtained by the reflection of of light emitted by itself. It cannot be constrained by time and space, and the beam is quasi-parallel light, which avoids the inherent optical distortion error of conventional optical measurement. (5) light emitted by itself. It cannot be constrained by time and space, and the beam is quasi-parallel light, light, which avoids the inherent optical distortion error of conventional optical measurement. (5) High density and high precision: Laser scanning obtains target characteristics in a high-density and which avoids the inherent optical distortion error of conventional optical measurement. (5) High density High density and high precision: Laser scanning obtains target characteristics in a high-density and high-precision way. The laser point cloud is composed of point position coordinate data. Using a and high precision: Laser scanning obtains target characteristics in a high-density and high-precision way. high-precision way. The laser point cloud is composed of point position coordinate data. Using a large lattice and a certain density grid to describe the entity information, the target information can The laser point cloud is composed of point position coordinate data. Using a large lattice and a certain large lattice and a certain density grid to describe the entity information, the target information can be described more accurately. density grid to describe the entity information, the target information can be described more accurately. be described more accurately. Three-dimensional laser scanning devices are placed in five boreholes, as shown in Figure 15. Three-dimensional laser scanning devices are placed in five boreholes, as shown in Figure 15. Three-dimensional laser scanning devices are placed in five boreholes, as shown in Figure 15. (a) (b) (c) (a) (b) (c) Figure 14. Laser scanning equipment and operation interface. (a,b) Laser scanning equipment; (c) Figure 14. Figure 14. Laser scanning eq Laser scanning equipment uipment and operation interf and operation interface. ace. (a,b() La a,b)se Laser r scanning scanning equiequipment; pment; (c) operation interface. operation inter (c) operation interface. face. Figure 15. Karst cave distribution map. Figure 15. Karst cave distribution map. Figure 15. Karst cave distribution map. 3.3. Three-Dimensional Model of Karst Cave 3.3. Three-Dimensional Model of Karst Cave 3.3. Three-Dimensional Model of Karst Cave h1 measured a cave about 1 m high at about 19.1 m underground, with a volume of about 2 cubic h1 measured a cave about 1 m high at about 19.1 m underground, with a volume of about 2 cubic h1 measured a cave about 1 m high at about 19.1 m underground, with a volume of about 2 cubic meters. The three-dimensional model of the cave is shown in Figure 16. meters. The three-dimensional model of the cave is shown in Figure 16. meters. The three-dimensional model of the cave is shown in Figure 16. Appl. Sci. 2019, 9, 2588 12 of 17 Appl. Sci. 2019, 9, x 12 of 17 Appl. Sci. 2019, 9, x 12 of 17 Appl. Sci. 2019, 9, x 12 of 17 Figure 16. The three-dimensional model of the cave (h1). Figure 16. The three-dimensional model of the cave (h1). Figure 16. The three-dimensional model of the cave (h1). Figure 16. The three-dimensional model of the cave (h1). h2 h2 m measur easure ed d a a cave cave about about 1 1.5 .5 m m high high at at a about bout 21 m 21 m un under dergro ground, und, w with ith a volum a volume e of ab of about out 3 3 cub cubic ic h2 measured a cave about 1.5 m high at about 21 m underground, with a volume of about 3 cubic h2 measured a cave about 1.5 m high at about 21 m underground, with a volume of about 3 cubic meters. meters. The t The thr hree-d ee-dimensional imensional model of model of t the he cave cave is is sh shown own in in Figur Figure e 1 17 7.. meters. The three-dimensional model of the cave is shown in Figure 17. meters. The three-dimensional model of the cave is shown in Figure 17. Figure 17. The three-dimensional model of the cave (h2). Figure 17. The three-dimensional model of the cave (h2). Figure 17. The three-dimensional model of the cave (h2). Figure 17. The three-dimensional model of the cave (h2). h3 measured the beaded cave at about 19–22.5 m from the ground, with a volume of about 3.44 h3 measured the beaded cave at about 19–22.5 m from the ground, with a volume of about 3.44 h3 measured the beaded cave at about 19–22.5 m from the ground, with a volume of about 3.44 h3 measured the beaded cave at about 19–22.5 m from the ground, with a volume of about 3.44 and 3.6 cubic meters, respectively. The three-dimensional model of the cave is shown in Figure 18. and 3.6 cubic meters, respectively. The three-dimensional model of the cave is shown in Figure 18. and 3.6 cubic meters, respectively. The three-dimensional model of the cave is shown in Figure 18. and 3.6 cubic meters, respectively. The three-dimensional model of the cave is shown in Figure 18. Figure 18. The three-dimensional model of the cave (h3). Figure 18. The three-dimensional model of the cave (h3). Figure 18. The three-dimensional model of the cave (h3). Figure 18. The three-dimensional model of the cave (h3). h4 measured the cavern at about 2.8–20.5 m from the ground, with a volume of about 9 cubic h4 measured the cavern at about 2.8–20.5 m from the ground, with a volume of about 9 cubic h4 measured the cavern at about 2.8–20.5 m from the ground, with a volume of about 9 cubic h4 measured the cavern at about 2.8–20.5 m from the ground, with a volume of about 9 cubic meters. The three-dimensional model of the cave is shown in Figure 19. meters. The three-dimensional model of the cave is shown in Figure 19. meters. The three-dimensional model of the cave is shown in Figure 19. meters. The three-dimensional model of the cave is shown in Figure 19. Appl. Sci. 2019, 9, x 13 of 17 Appl. Sci. 2019, 9, x 13 of 17 Appl. Sci. 2019, 9, x 13 of 17 Appl. Sci. 2019, 9, x 13 of 17 Appl. Sci. 2019, 9, 2588 13 of 17 Appl. Sci. 2019, 9, x 13 of 17 Appl. Sci. 2019, 9, x 13 of 17 Figure 19. The three-dimensional model of the cave (h4). Figure 19. The three-dimensional model of the cave (h4). Figure 19. The three-dimensional model of the cave (h4). Figure 19. The three-dimensional model of the cave (h4). h5 measured caves at about 16–21.5 m from the ground with a vol ume of about 2.1–2.7 cubic h5 measured caves at about 16–21.5 m from the ground with a volume of about 2.1–2.7 cubic h5 measured caves at about 16–21.5 m from the ground with a volume of about 2.1–2.7 cubic Figure 19. The three-dimensional model of the cave (h4). h5 measured caves at about 16–21.5 m from the ground with a volume of about 2.1–2.7 cubic Figure 19. The three-dimensional model of the cave (h4). meters. The three-dimensional model of the cave is shown in Figure 20. meters. The three-dimensional model of the cave is shown in Figure 20. Figure 19. The three-dimensional model of the cave (h4). meters. The three-dimensional model of the cave is shown in Figure 20. meters. The three-dimensional model of the cave is shown in Figure 20. h5 measured caves at about 16–21.5 m from the ground with a volume of about 2.1–2.7 cubic h5 measured caves at about 16–21.5 m from the ground with a volume of about 2.1–2.7 cubic h5 measured caves at about 16–21.5 m from the ground with a volume of about 2.1–2.7 cubic meters. The three-dimensional model of the cave is shown in Figure 20. meters. The three-dimensional model of the cave is shown in Figure 20. meters. The three-dimensional model of the cave is shown in Figure 20. Figure 20. Figure 20. The The three-dimensio three-dimensio nal model nal model of th of th e cave e cave (h5). (h5). Figure 20. The three-dimensional model of the cave (h5). Figure 20. The three-dimensional model of the cave (h5). Figure 20. The three-dimensional model of the cave (h5). Figure 20. The three-dimensional model of the cave (h5). The volume of each cave is shown in Table 2. The volume of each cave is shown in Table 2. The volume of each cave is shown in Table 2. Figure 20. The three-dimensional model of the cave (h5). The volume of each cave is shown in Table 2. The volume of each cave is shown in Table 2. The volume of each cave is shown in Table 2. Table 2. The volume of each cave. Table 2. The volume of each cave. Table 2. The volume of each cave. The volume of each cave is shown in Table 2. Table 2. The volume of each cave. Table 2. The volume of each cave. Table 2. The volume of each cave. Drill Hole Limestone Cave Volume (m ) Drill Hole Limestone Cave Volume (m 3) Drill Hole Limestone Cave Volume (m3 ) Drill Hole Limestone Cave 3 Volume (m ) Drill Hole Table 2. L The imesto volume of ea ne Cave ch cave. Volume (m ) Drill Hole Limestone Cave Volume (m ) Drill Hole Limestone Cave Volume (m ) h1 3.02 h1 3.02 h1 3.02 h1 3.02 h1 3.02 h1 3.02 h1 3.02 h2 3.89 h2 h2 3. 3. 89 89 h2 h2 3.89 3.89 h2 3.89 h2 3.89 3.44 3.44 3.44 3.44 3.44 3.44 h3 h3 h3 h3 h3 h3 3.44 3.66 3.66 3.66 3.66 3.66 3.66 h3 3.66 Appl. Sci. 2019, 9, 2588 14 of 17 Table 2. Cont. Appl. Sci. 2019, 9, x 14 of 17 Appl. Sci. 2019, 9, x 14 of 17 Appl. Appl. Sci. Sci. 2019 2019, , 9 9, x , x 14 of 14 of 17 17 Appl. Sci. 2019, 9, x 14 of 17 Drill Hole Limestone Cave Volume (m ) h4 3.84 h4 h4 h4 h4 3.84 3. 3. 3.84 84 84 h4 3.84 3.15 3.15 3. 3. 3.15 15 15 3.15 h5 h5 3.7 h5 h5 h5 3.7 3.7 3. 3.7 7 h5 3.7 3.29 3.29 3. 3. 3.29 29 29 3.29 At the same time, the high-definition camera function was mounted on the laser three- At the same time, the high-definition camera function was mounted on the laser three-dimensional At At At t t thh he s e s e saaame me me t t tiiime, me, me, t t thh he h e h e hiiigh-de gh-de gh-defin fin finitit ition ion ion camer camer cameraaa functi functi function was m on was m on was mooounted on the la unted on the la unted on the laser three- ser three- ser three- At the same time, the high-definition camera function was mounted on the laser three- dimensional detection system. The results are shown in Figure 21. detection dimensional system. detection sy The results stem. The are shown resu in lts are Figur shown e 21. in Figure 21. dimensional dimensional detection sy detection system. The stem. The re resu sults are lts are shown shown in Fig in Figu ure re 21. 21. dimensional detection system. The results are shown in Figure 21. Figure 21. Intra-hole photography. Figure Figure 21. 21. Intra-hole Intra-hole photography. photography. Figure 21. Figure 21. Intr Intra-hole photography. a-hole photography. Figure 21. Intra-hole photography. 4. T 4. reatment Treatment of Karst of Kars Cave t Cave 4. 4. 4. T T Trr re e ea a atm tm tment ent ent of Kars of Kars of Karstt t C C Ca a av v ve e e 4. Treatment of Karst Cave During the construction of metro, it is easy to cause the risk of ground subsidence. If there are During the construction of metro, it is easy to cause the risk of ground subsidence. If there are Duri Duri During the constructi ng the constructi ng the construction of on of on of metro, i metro, i metro, itt t iiiss s ea ea easy to sy to sy to cc ca a ause use use the risk o the risk o the risk off f gr gr ground subside ound subside ound subsiden n nce. If there ce. If there ce. If there are are are During the construction of metro, it is easy to cause the risk of ground subsidence. If there are kars ka t crst ca aves ves above the sub above the subway,w tha eyr, the isk ofrig sk of roun ground d collapsc eoillapse ncrease incre s sha arse pls sh y. Tarply. hereforTherefore e, the abo,v the above e karst ka ka karst ca rst ca rst caves above the sub ves above the sub ves above the subw w waa ay y y, the , the , the ri ri risk of sk of sk of ground ground ground cc co o ollapse llapse llapse incre incre increaa ase se ses sh s sh s sharply. arply. arply. Therefore Therefore Therefore,,, the above the above the above karst caves above the subway, the risk of ground collapse increases sharply. Therefore, the above karst caves need to be harnessed. Sufficient safety distance should be ensured for karst caves under caves need to be harnessed. Sufficient safety distance should be ensured for karst caves under metro. kar kar karss st caves n t caves n t caves need to be har eed to be har eed to be harn n nessed essed essed... Suffic Suffic Sufficient safety ient safety ient safety d d diiistance sho stance sho stance shou u uld ld ld be ensur be ensur be ensured for kar ed for kar ed for karss st cave t cave t caves under s under s under karst caves need to be harnessed. Sufficient safety distance should be ensured for karst caves under If th metro. If the sa e safety distanf ce ety di from sta th ne ce f floro om r is the toofs lo m or is too all, it is sm easal y l, to itc is ea ausesy to the scau ettle se m the settl ent of th ement of e subwa the subway y tunnel. metro. If the sa metro. If the sa metro. If the saff fe e ety di ty di ty dista sta stan n nce f ce f ce fr r rom om om the the the ff fll lo o oor is too or is too or is too sm sm smal al all, l, l, ii itt t is ea is ea is easy to sy to sy to cau cau caus s se e e the settl the settl the settlement of ement of ement of the subway the subway the subway metro. If the safety distance from the floor is too small, it is easy to cause the settlement of the subway tunnel. According to the design experience, it is necessary to treat the floor karst cave within twice tt tu u unnel. nnel. nnel. Accor Accor Accord d ding t ing t ing to o o t t th h he d e d e de e esign sign sign experi experi experie e en n nce, it ce, it ce, it is ne is ne is necessary to trea cessary to trea cessary to treat the f t the f t the fllloor oor oor karst ca karst ca karst cave wi ve wi ve withi thi thin n n twi twi twicc ce e e tunnel. According to the design experience, it is necessary to treat the floor karst cave within twice the diameter of the tunnel. For the karst caves on both sides of metro tunnel, the disturbance effect of the diameter of the tunnel. For the karst caves on both sides of metro tunnel, the disturbance effect of the dia the diam meter eter of of the tunnel. the tunnel. For the ka For the karst rst ca caves on bo ves on both si th sides of metro tunnel des of metro tunnel, , the the disturb disturba ance nce e effect ffect of of the diameter of the tunnel. For the karst caves on both sides of metro tunnel, the disturbance effect of shield excavation is mainly considered. According to engineering experience, when shield machine shie shie shield exc ld exc ld exca a ava va vatt tiiion is m on is m on is ma a ain in inly ly ly conside conside considerr red. ed. ed. Accordin Accordin According to engineer g to engineer g to engineering ing ing e e ex x xperience, w perience, w perience, wh h hen shie en shie en shield m ld m ld ma a achine chine chine shield excavation is mainly considered. According to engineering experience, when shield machine is excavated, the influence of karst caves beyond 5 m on both sides of the tunnel is small, only the is excavated, the influence of karst caves beyond 5 m on both sides of the tunnel is small, only the is excav is excava ated, ted, the in the influence fluence of of kar kars st c t ca aves beyond ves beyond 5 5 m m on both si on both sides of the tu des of the tunnel is nnel is smal small, l, only the only the is excavated, the influence of karst caves beyond 5 m on both sides of the tunnel is small, only the Appl. Sci. 2019, 9, 2588 15 of 17 According to the design experience, it is necessary to treat the floor karst cave within twice the diameter of the tunnel. For the karst caves on both sides of metro tunnel, the disturbance effect of shield excavation is Appl. Sci. 2019, 9, x 15 of 17 mainly considered. According to engineering experience, when shield machine is excavated, the influence of karst caves beyond 5 m on both sides of the tunnel is small, only the karst caves within 5 m need karst caves within 5 m need to be treated. Reserve special holes for karst treatment in the segment to be treated. Reserve special holes for karst treatment in the segment structure for newly discovered structure for newly discovered karst caves during tunnel excavation and areas where settlement karst caves during tunnel excavation and areas where settlement exceeds, or abnormality occurs in the exceeds, or abnormality occurs in the later stages of the tunnel. Supplementary drilling is carried out later stages of the tunnel. Supplementary drilling is carried out in every 10 annular segments along the in every 10 annular segments along the line, and the drilling depth is twice as far down as the tunnel line, and the drilling depth is twice as far down as the tunnel bottom. According to the drilling results, bottom. According to the drilling results, grouting filling is carried out at the tunnel bottom to ensure grouting filling is carried out at the tunnel bottom to ensure the safety of operation. the safety of operation. If a karst cave is found, it can be treated. For a karst cave whose diameter is less than 1 m, If a karst cave is found, it can be treated. For a karst cave whose diameter is less than 1 m, the the volume is smaller and the cement slurry needed for filling is less. Pressure grouting with 1:1 volume is smaller and the cement slurry needed for filling is less. Pressure grouting with 1:1 cement cement slurry is directly applied to non-filled and semi-filled karst caves whose height is not more than slurry is directly applied to non-filled and semi-filled karst caves whose height is not more than 1 m. 1 m. For karst caves with a larger diameter, the volume required is larger. Sand blowing treatment For karst caves with a larger diameter, the volume required is larger. Sand blowing treatment can be can be carried out first, and then grouting reinforcement can be carried out. The small void of sand carried out first, and then grouting reinforcement can be carried out. The small void of sand is is conducive to cement deposition, reduces the di usion of cement slurry in the range of ine ective conducive to cement deposition, reduces the diffusion of cement slurry in the range of ineffective di usion, and e ectively reduces the filling cost while guaranteeing the strength. diffusion, and effectively reduces the filling cost while guaranteeing the strength. Through the limestone section, the uniaxial saturated compressive strength of limestone lies in the Through the limestone section, the uniaxial saturated compressive strength of limestone lies in range of 34–83 MPa, the buried depth of the left tunnel is 14.7–25.4 m, and the buried depth of the right the range of 34–83 MPa, the buried depth of the left tunnel is 14.7–25.4 m, and the buried depth of the tunnel is 14.7–25.2 m. The current maximum water level is 5.2 m below the ground, the anti-floating right tunnel is 14.7–25.2 m. The current maximum water level is 5.2 m below the ground, the anti- waterproof level is 1.9 m below the ground, and the maximum water head height at the bottom of the floating waterproof level is 1.9 m below the ground, and the maximum water head height at the left and right tunnels is 23.5 m during the whole operation period. When the allowable opening of bottom of the left and right tunnels is 23.5 m during the whole operation period. When the allowable segment joint is 6 mm, the elastic gasket can still resist water pressure of 0.8 MPa. Considering the high opening of segment joint is 6 mm, the elastic gasket can still resist water pressure of 0.8 MPa. strength of rocks, the development of karst and fractured zones, the abundant karst water, the dicult Considering the high strength of rocks, the development of karst and fractured zones, the abundant control of tunneling posture during shield tunneling, and the diculty in reaching the ideal state of karst water, the difficult control of tunneling posture during shield tunneling, and the difficulty in segment assembling quality, in order to improve the waterproofing ability of shield segments, flexible reaching the ideal state of segment assembling quality, in order to improve the waterproofing ability seams with full rings are used in rock-piercing sections (Figure 22). of shield segments, flexible seams with full rings are used in rock-piercing sections (Figure 22). Figure 22. Figure 22. Drawing of grouting borehole. Drawing of grouting borehole. 5. Conclusions 5. Conclusions 1. The apparent resistivity of karst caves is higher than that of relatively intact strata. In a complex 1. The apparent resistivity of karst caves is higher than that of relatively intact strata. In a complex urban environment, high-density electrical method and transient electromagnetic method have urban environment, high-density electrical method and transient electromagnetic method have high resolution for karst caves. Through the results of geophysical prospecting, targeted drilling high resolution for karst caves. Through the results of geophysical prospecting, targeted drilling can be carried out to avoid blind drilling. can be carried out to avoid blind drilling. 2. The laser point cloud is composed of point position coordinate data. Using a large lattice and a certain density grid to describe the entity information, the target information can be described more accurately. Making full use of the target drill hole and fine scanning of the cave via a 3-D automatic laser scanner, parameters such as the real shape and volume of the cave were obtained. Appl. Sci. 2019, 9, 2588 16 of 17 2. The laser point cloud is composed of point position coordinate data. Using a large lattice and a certain density grid to describe the entity information, the target information can be described more accurately. Making full use of the target drill hole and fine scanning of the cave via a 3-D automatic laser scanner, parameters such as the real shape and volume of the cave were obtained. 3. According to the construction experience and design principle, the treatment scope and method of karst caves in di erent locations are determined. The karst caves above the metro must be filled. The karst caves below the tunnel within twice the diameter need to be filled. The karst caves within 5 m on both sides of the tunnel need to be filled. When the diameter of karst cave is less than 1 m, it can be filled with cement slurry directly. When the diameter of karst cave is larger than 1 m, it needs to be filled with sand before grouting. Author Contributions: Conceptualization, J.W. and L.L.; Methodology, S.S. (Shaoshuai Shi); Software, S.S. (Shangqu Sun); Validation, J.W., L.L. and S.S. (Shaoshuai Shi); Formal Analysis, J.W.; Investigation, S.S. (Shaoshuai Shi); Resources, J.W.; Data Curation, S.S. (Shangqu Sun); Writing—Original Draft Preparation, X.B.; Writing—Review & Editing, Y.Z.; Visualization, X.B.; Supervision, L.L.; Project Administration, L.L.; Funding Acquisition, J.W. Funding: The work is supported by National Natural Science Foundation of China (Grant No. 51809158, 51609129, 51809157), Shandong Provincial Natural Science Foundation, China (Grant No. ZR2018BEE045), China Postdoctoral Science Foundation (2018M630780). Conflicts of Interest: The authors declare no conflict of interest. References 1. Sun, S.; Li, L.; Wang, J.; Shi, S.; Song, S.; Fang, Z.; Ba, X.; Jin, H. Karst Development Mechanism and Characteristics Based on Comprehensive Exploration along Jinan Metro, China. Sustainability 2018, 10, 3383. [CrossRef] 2. Foley, A.E. The Use and Development of Some Groundwater Tracing Techniques for Wellhead Protection: Studies from the Corallian Limestone of Yorkshire. Ph.D. Thesis, University College London, 2006. 3. Hui, G.; Xu, J. A numerical simulation of impact of groundwater seepage on temperature distribution in karst collapse pillar. Arab. J. Geosci. 2017, 10, 10. 4. Li, S.; Liu, B.; Nie, L.; Liu, Z.; Tian, M.; Wang, S.; Su, M.; Guo, Q. Detecting and monitoring of water inrush in tunnels and coal mines using direct current resistivity method: A review. J. Rock Mech. Geotech. Eng. 2015, 7, 469–478. [CrossRef] 5. Zhong, S.; Wang, R. New Landsonar Method for Survey of Ground in Busy Town, Karst Caves in Mountain and Sea Bottom on Water. J. Eng. Geol. 2013, 21, 422–432. 6. Peng, C. The Combined Application of Seismic Imaging Method and High-Density Electric Method to the Survey of Karst CollapseAreas. Chin. J. Eng. Geophys. 2016, 13, 60–63. 7. Knapp, R.W.; Steeples, D.W. High-resolution common-depth-point reflection profiling: Field acquisition parameter design. Geophysics 1986, 51, 283–294. [CrossRef] 8. Carbonel, D.; Rodríguez, V.; Gutiérrez, F.; McCalpin, J.P.; Linares, R.; Roqué, C.; Zarroca, M.; Guerrero, J.; Sasowsky, I. Evaluation of trenching, ground penetrating radar (GPR) and electrical resistivity tomography (ERT) for sinkhole characterization. Earth Surf. Process. Landf. 2014, 39, 214–227. [CrossRef] 9. Ardestani, V.E. Detecting, delineating and modeling the connected solution cavities in a dam site via microgravity data. Acta Geod. Geophys. 2013, 48, 123–138. [CrossRef] 10. He, W.; Yu, R. Application of High-Density Resistivity Survey to Reconnaissance the Highway’s Geological Disaster in the Mountainous Area. Geotech. Investig. Surv. 2009, 37, 89–94. 11. Xue, G.; Li, X.; Di, Q. The Progress of TEM in Theory and Application. Prog. Geophys. 2007, 22, 1195–1200. 12. Milsom, J.; Eriksen, A. Ground Penetrating Radar. In Groundwater Geophysics; Wiley: Chichester, UK, 1998. 13. Al-Fares, W.; Bakalowicz, M.; Guérin, R.; Dukhan, M. Analysis of the karst aquifer structure of the Lamalou area (Hérault, France) with ground penetrating radar. J. Appl. Geophys. 2004, 51, 97–106. [CrossRef] 14. Li, S.; Li, S.; Zhang, Q.; Xue, Y.; Ding, W.; Zhong, S.; He, F.; Lin, Y. Forecast of Karst-Fractured Groundwater and Defective Geological Condition. Chin. J. Rock Mech. Eng. 2007, 26, 217–225. 15. Jiang, W. Combination of Geophysical and Conventional Boring Methods for the Investigation of an Industrial Building over Abandoned Mining Areas in Zhangqiu. Soil Eng. Found. 2017, 3, 364–368. Appl. Sci. 2019, 9, 2588 17 of 17 16. Waltham, D.T.; Bell, F.G.; Culshaw, M.G. Sinkholes and Subsidence; Springer: Berlin, Germany, 2005. 17. Yang, B.; Fang, L. Automated Extraction of 3-D Railway Tracks from Mobile Laser Scanning Point Clouds. IEEE J. Sel. Top. Appl. Earth Obs. Remote Sens. 2015, 7, 4750–4761. [CrossRef] 18. Gallay, M.; Hochmuth, Z.; Kanuk, ˇ J.; Hofierka, J. Geomorphometric analysis of cave ceiling channels mapped with 3-D terrestrial laser scanning. Hydrol. Earth Syst. Sci. 2016, 20, 1827. [CrossRef] 19. Ordóñez, C.; Cabo, C.; Sanzablanedo, E. Automatic Detection and Classification of Pole-Like Objects for Urban Cartography Using Mobile Laser Scanning Data. Sensors 2017, 17, 1465. [CrossRef] [PubMed] 20. Liu, G.; Meng, X.; Ni, J.; Chen, Z.; Zhang, D. Evaluation of the two-dimension reflection seismic method towards the exploration of thrust-controlled mineral deposits in southwestern Fujian province, China. Geophysics 2018. [CrossRef] 21. Zhong, S. Land sonar method and e ectiveness. Geophys. Geochem. Explor. 1997, 21, 172–179. 22. Guo, D.D.; Zhao, L.H.; Gao, Z.J. High-density electrical method used in the application of karst collapse. Ground Water 2011, 33, 108–110. 23. Christiansen, A.V.; Auken, E.; Sørensen, K. The transient electromagnetic method. In Groundwater Geophysics; Springer: Berlin/Heidelberg, Germany, 2006; pp. 179–226. 24. Li, X.; Xue, G.; Yin, C. Migration Imaging of the Transient Electromagnetic Method; Springer: Singapore, 2017. 25. Arifi, M.H.; Jamaluddin, T.A.; Husin, H.; Ismail, A.; Abbas, A.A.; Nordin, M.N.M.; Othman, N.A. Comparison of Geological Mapping with Electrical Resistivity and Ground Penetration Radar Methods for Rock Fractured System Study. Chiang Mai J. Sci. 2016, 43, 1346–1357. 26. Annan, A.P.; Diamanti, N.; Redman, J.D.; Jackson, S.R. Ground-penetrating radar for assessing winter roads. Geophysics 2016, 81, WA101–WA109. [CrossRef] 27. Orfanos, C.; Apostolopoulos, G. 2D–3D resistivity and microgravity measurements for the detection of an ancient tunnel in the Lavrion area, Greece. Near Surf. Geophys. 2011, 9, 449–457. [CrossRef] © 2019 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (http://creativecommons.org/licenses/by/4.0/).

Journal

Applied Sciences – Multidisciplinary Digital Publishing Institute

Published: Jun 26, 2019

There are no references for this article.