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Engineering geological characteristics of the underground surge pool cavern: a case study, India

Engineering geological characteristics of the underground surge pool cavern: a case study, India anaithania@gmail.com National Institute of Rock For better rock mass characterization, 3D engineering geological mapping and in-situ Mechanics, Bengaluru, India testing was carried for the heading portion of surge pool of Palamuru Ranga Reddy lift irrigation scheme lift-II. The direction of the longest axis of the surge pool cavern was finalized based on the in-situ hydrofracturing testing inside the borehole and aligning the appurtenant structures of pump house and surge pool cavern on the ground. Rock types mapped were grey and pink granites belongs to the Peninsular Gneissic Complex of Archaean age. The assessment of Tunnel Quality Index ‘Q’ for the exposed granitic rock mass was done based on the information available of the rock joints and their nature, 3D geological mapping and in-situ stress measurement. The rock mass quality (Q) is related with the ultimate support pressure requirement. Excavation Support Ratio (ESR) as given in the ESR updated classification standard of NMT Q-system is applied to 1.0 for this cavern. On the basis of NMT Q-system chart and site geological characteris- tics, support system is recommended and its efficacy is assessed. Keywords: Engineering geology, Surge pool cavern, Support system, Rock bolt, Steel fibre reinforced shotcrete Introduction 357.00  m long, 89.81  m high and 31.00  m wide underground surge pool cavern for a lift irrigation scheme is being constructed in the part of Telangana State of India. The main design approaches for underground cavern excavation in rock are analytical, observational, and empirical. In this paper empirical approach for support design of underground surge pool cavern of a Palamuru Ranga Reddy lift irrigation scheme lift- II (PRLIS-L-II) is discussed. Rock mass classifications as practiced in civil and mining engineering works form an integral part of the empirical design methods, which is the most predominant design approach [4]. The main objectives of the rock mass classifica - tions are to identify the most significant parameters influencing the behavior of a rock mass, divide area into rock mass classes of varying quality and provide quantitative data for engineering design purpose. Empirical approaches are developed for the stability of underground structures based on the large number of case studies. © The Author(s) 2022. Open Access This article is licensed under a Creative Commons Attribution 4.0 International License, which permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons licence, and indicate if changes were made. The images or other third party material in this article are included in the article’s Creative Commons licence, unless indicated otherwise in a credit line to the mate- rial. If material is not included in the article’s Creative Commons licence and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder. To view a copy of this licence, visit http:// creat iveco mmons. org/ licen ses/ by/4. 0/. Naithani et al. International Journal of Geo-Engineering (2022) 13:7 Page 2 of 12 Table 1 Summary of input data 1. Length of surge pool 357.00 m 9. Rise of arc 9.00 m 2. Excavated width of cavern (B) 31.00 m 10. Bottom floor level 274.19 m 3. Height of surge pool 89.81 m 11. Minimum down surge level 313.89 m 4. Height of surge pool walls 80.81 m 12. Maximum upsurge level 341.80 m 5. Crown level 364.00 m 13. Service bay level 346.0 m 6. Spring level 355.00 m 14. Vertical stress (σ ) 3.44 MPa 7. Height of overburden above 67.48 m (average) 15. Maximum horizontal principal 5.46 ± 1.23 MPa crown (H) stress (σ ) 8. Ground levels 431.48 m 16. Minimum horizontal principal 3.64 ± 0.82 MPa stress (σ ) Fig. 1 3D view of pump house complex including surge pool and pump house For surge pool cavern of PRLIS lift-II, rock mass characterization was done based on 3D geologic mapping and in-situ stress measurement. For the orientation of the long axis of the surge pool underground cavern, hydrofrac test inside the NX bore- hole BH-01 was carried out by NIRM. Vertical borehole (BH-01) of 130 m depth was drilled from the surface. From this test, magnitudes of the principal stresses as well as the direction of maximum horizontal principal stress were determined. After detailed analysis it was concluded that the K-value (σ /σ = 1.58) indicates a medium stress H v magnitude and the maximum horizontal principal stress direction N30°, which was recommended for the orientation of the long axis of the cavity to reduce ground con- trol problems [1]. For this cavern the vertical cover is more than 67 m and summary of input data used for the recommendation of support system for underground surge pool cavern is given in Table  1 and 3D view of pump house complex including surge pool and pump house is given in Fig. 1. Naithani  et al. International Journal of Geo-Engineering (2022) 13:7 Page 3 of 12 Site geological condition Surge pool site of Palamuru Ranga Reddy lift irrigation scheme lift-II forms a part of the Peninsular Shield of the Indian Sub-continent [16]. The site forms a part of Eastern Block of Dharwar Craton mainly comprised of Archaean granites which are intruded by mafic dykes age ranging from Archaean to Upper Proterozoic [18]. Gran - ites and gneisses are exposed in and around the surge pool area. Granites and gneisses have deformational history documenting three phases of folding [7, 16]. Granites and gneisses are intruded by different types of younger granites [17]. The surge pool area exhibits a gently undulated topography with isolated hillocks and undulated hilly terrain with intermittent broad valley portions. On the surface along the surge pool alignment medium to coarse grained pink/grey granites were exposed. 3D engineering geological mapping of the heading portion of surge pool cavern was carried out in 1:100 scale. This will be a permanent record of all geologic defects pre - sent in the excavated portion. After proper cleaning and scaling, in adequate lighting geological logging was done. Rock types mapped after the excavation were grey and pink granite belongs to the Peninsular Gneissic Complex of Archaean age [15, 16]. Granites were medium to coarse grained, hard, jointed and fresh in nature. The rock mass was characterized by generally two plus random joint sets, which were generally more than 15 m in persistent, slightly rough, rough undulating, rough planar to smooth planar, with unaltered joint walls (Table  2). Minor staining has been recorded along some joint surfaces. Joints were moderately to widely spaced in nature. The rock mass was characterized by dry condition. Minor cracks/fractures developed due to blasting were also recorded. About 20  cm wide dolerite dyke was recorded towards right side edge, where the granite rock mass was sheared at the contact with the dyke. Dolerite dyke was fresh, hard and compact in nature. However, the contact zones of dolerite and the adjoin- ing granite were slightly sheared. Along the contact zones i.e., over a width of 0.40 m, welded wire mesh was placed and 50  mm extra SFRS layer was put to prevent any rock fall during benching down. Table 2 Joint sets recorded in pink/grey granite Joint sets Azimuth/ Spacing Strike Roughness Aperture Infilling Ground dip amount (cm) length (m) (mm) water J1 280–310/V 20–60 > 20 Slightly Tight to 1 Fresh/ Dry rough, stained smooth planar J2 220/10–15 30–40 10–20 Slightly Tight to 1 Fresh/ Dry rough, stained smooth planar J3 220/V 20–70 > 20 Rough undu- Tight to 1 Fresh/ Dry lating stained J4 130/60–65 30–40 > 15 Smooth Tight to 1 Fresh/ Dry planar stained J5 30–50/V 20–70 > 20 Rough Tight Fresh Dry planar Naithani et al. International Journal of Geo-Engineering (2022) 13:7 Page 4 of 12 Rock mass classification The rock mass of the heading portion of surge pool cavern was classified based on tun - nelling quality index (Q). Based on six parameters i.e. rock quality designation (RQD), number of joint sets (J ), joint roughness number (J ), joint alteration number (J ), joint n r a water reduction factor (J ) and stress reduction factor (SRF), the Q-values are calculated using the Eq. (1) [2, 5, 6]. High Q-values means good stability while low Q-values indi- cates poor stability. World-wide this classification is being used for the characterization of rock mass of an underground opening in jointed rock masses. RQD J J r w Q = + + (1) J J SRF n a All the parameters were determined during geological mapping using tables that give numerical values to be assigned to a described situation. All the discontinuities per 5 m length were taken into consideration for the calculation of Q-values and in general two plus random (R) joint sets were intersecting at 5 m length and circumference. RQD val- ues were ranging from 60 to 80% and average RQD value was 70%. Total excavation was done in dry condition. The assessment of Q-values based on the information available of the rock joints and their nature and 3D geological logging, is tabulated in Table 3. Roof support pressure, wall support pressure and ground squeezing condition were estimated based on Q-values. The grade of rock mass based on the rock joints characteristics has the Q-values varying from 3.89 to 13.33, and it comes under poor to good rock mass category. The average Q-value calculated is 10.87. The poor Q-value was estimated at the intersection portion only. Estimation of support pressure and ground squeezing condition Barton et  al. [2] gives an empirical equation relating rock mass quality ‘Q’ and perma- nent support pressure based on the case records Eq.  (2). They also give an improved empirical fit by incorporating separate weighting for the number of joint sets (J ) Eq. (3). For the surge pool cavern of PRLIS lift-II, roof support and wall support pressures are estimated as per Eqs. (4) and (5), which are applicable for the non-squeezing ground condition [8, 19]. 2.0 −1/3 P = Q roof (2) 1/2 −1/3 2J (Q) P = (3) roof 3J 2.0 −1/3 P = Q × f roof (4) 2.0 −1/3 P = Q × f Wall (5) r Naithani  et al. International Journal of Geo-Engineering (2022) 13:7 Page 5 of 12 Table 3 Q-values recorded from the heading portion of the surge pool Chainage Rock type Rock quality Number Joint Joint Joint water Stress Q (m) designation of joint roughness alteration reduction reduction Value Class (%) sets number number factor factor 0–10 Medium 70 2 + R Smooth, Unaltered Dry excava- Medium 3.89 Poor to coarse (intersec- planar tion stress granite tion) 10–25 Medium 70 2 + R Smooth, Unaltered, Dry excava- Medium 11.67 Good to coarse planar stained tion stress granite 25–50 Medium 65 2 + R Smooth, Unaltered Dry excava- Medium 10.83 Good to coarse planar tion stress granite 50–75 Medium 80 2 + R Smooth, Unaltered Dry excava- Medium 13.33 Good to coarse planar tion stress granite 75–100 Medium 75 2 + R Smooth, Unaltered, Dry excava- Medium 12.50 Good to coarse planar stained tion stress granite 100–125 Medium 70 2 + R Smooth, Unaltered, Dry excava- Medium 11.66 Good to coarse planar stained tion stress granite 125–150 Medium 75 3 Smooth, Unaltered Dry excava- Medium 8.33 Fair to coarse planar tion stress granite 150–175 Medium 80 2 + R Smooth, Unaltered, Dry excava- Medium 13.33 Good to coarse planar stained tion stress granite 175–200 Medium 60 2 + R Smooth, Unaltered Dry excava- Medium 10.00 Good to coarse planar tion stress granite 200–239 Medium 70 2 + R Smooth, Unaltered, Dry excava- Medium 11.67 Good to coarse planar stained tion stress granite 239–260 Medium 65 2 + R Smooth, Unaltered, Dry excava- Medium 10.83 Good to coarse planar stained tion stress granite 260–285 Medium 60 2 + R Smooth, Unaltered Dry excava- Medium 10.00 Good to coarse planar tion stress granite 285–300 Medium 70 2 + R Smooth, Unaltered, Dry excava- Medium 11.67 Good to coarse planar stained tion stress granite 300–357 Medium 75 2 + R Smooth, Unaltered Dry excava- Medium 12.50 Good to coarse planar tion stress granite where P is permanent/ultimate roof support pressure in kg/cm , P is ultimate wall roof wall support pressure in kg/cm , Jr is joint roughness number, Q is rock mass quality, Q is wall quality/factor equal to 2.5Q for intermediate qualities (0.1 < Q < 10) and 5Q for good qualities (Q > 10) in case of medium stress, J is joint set number and f is correction factor for overburden. Correction factor for overburden can be estimated from Eq. (6), where ‘H’ is the height of overburden above crown in metres. (H − 320) (67.48 − 320) f = 1 + ≥ 1 = 1 + = 0.68 (6) 800 800 For the estimation of non-squeezing ground condition Singh et al. [19] suggested an empirical approach Eq. (7) based on case histories and by collecting Barton et al. [2] Naithani et al. International Journal of Geo-Engineering (2022) 13:7 Page 6 of 12 ‘Q’ data and overburden (H). Minimum Q-value is used for the estimation of ground squeezing condition. Ground condition is non-squeezing because above surge pool cavern, cover is 67.48  m only. The required support pressure for crown is varying 2 2 between 8.437 and 9.869 t/m and for walls 4.934–7.271 t/m (Table  4). The average 2 2 support pressure for crown is 8.927 t/m and for walls 5.336 t/m . 1/3 1/3 H < 350Q ; 67.48 < 350 × 8.33 = 709 (7) Rock support As per hydraulic design, the surge pool of lift-II scheme is having an excavated width of 31.00 m and length 357.00 m. The crown level of surge pool is kept at EL 364.00 m and bottom level at EL 274.19  m. As per hydraulic design, the maximum upsurge level of surge pool works out to EL 341.80  m and minimum down surge level works out to EL 313.89 m. Surge pool with 500 mm thick concrete lined in the lower portion is proposed. For the heading portion of surge pool cavern reinforcement support pattern using Nor- wegian Method of Tunnelling (NMT) Q-system was used. Excavation Support Ratio (ESR) of cavity as given in the ESR updated classification standard of NMT Q-system is applied to 1.0 [14]. The Equivalent Dimension (De) is applied by dividing the span (m) of surge pool cavern by the fore-mentioned ESR. Bolt length which is depend on excavation dimension can be estimated from the excavation span (B) and the excava- tion support ratio (ESR) [2, 3] Eq. (8). By applying this formula, the length of rock bolt for the crown is calculated to be 6.65 m. The value of NMT Q-system chart proposed is 7.0–8.0 m for the crown: 0.15B L = 2 + (8) roof ESR where L is bolt length in metres for roof, B is span in metres and ESR is the excavation roof support ratio. The Norwegian Institute for Rock Blasting Technique has proposed a formula Eq. (9) to estimate the length of the bolts in the central section of the opening where ‘B’ is the span of the opening in metres [22]. By applying this, the length of rock bolt for crown of surge pool is calculated to be 7.10 m Eq. (9). L = 1.40 + 0.184 B (9) The thickness of steel fibre reinforced shotcrete (t ) can be estimated from the ulti- fsc mate support pressure (P ), size of opening (B), mobilization factor for shotcrete roof (F   −  0.6 ± 0.05) and shear strength of steel fibre reinforced shotcrete (q   –  550  t/ fsc fsc m ) as per Eq. (10) [9]. The thickness of SFRS for crown is calculated from the average Q-value to be 150  mm. The value of NMT Q-system chart proposed is 70–90  mm for crown. P × B × F roof fsc t = fsc (10) 2q fsc Naithani  et al. International Journal of Geo-Engineering (2022) 13:7 Page 7 of 12 Table 4 Support pressure for the roof and walls of surge pool cavern Chainage (m) Q value for roof Q value for wall Joint roughness Joint alteration Ultimate roof support Ultimate wall support Jr/Ja Friction angle −1 number for crown & number for crown & pressure pressure φ = tan (J /J ) j r a wall wall 2 2 (kg/cm ) MPa (kg/cm ) MPa 0.0–10 3.89 9.73 1.0 1.0 1.272 0.125 0.937 0.092 1.00 45 10–25 11.67 58.35 1.0 1.0 0.882 0.086 0.516 0.051 1.00 45 25–50 10.83 54.15 1.0 1.0 0.904 0.089 0.529 0.052 1.00 45 50–75 13.33 66.65 1.0 1.0 0.844 0.083 0.493 0.048 1.00 45 75–100 12.50 62.50 1.0 1.0 0.862 0.085 0.504 0.049 1.00 45 100–125 11.66 58.30 1.0 1.0 0.882 0.086 0.516 0.051 1.00 45 125–150 8.33 20.83 1.0 1.0 0.987 0.097 0.727 0.071 1.00 45 150–175 13.33 66.65 1.0 1.0 0.844 0.083 0.493 0.048 1.00 45 175–200 10.00 50.00 1.0 1.0 0.928 0.091 0.543 0.053 1.00 45 200–239 11.67 58.35 1.0 1.0 0.882 0.086 0.516 0.051 1.00 45 239–260 10.38 51.90 1.0 1.0 0.917 0.090 0.536 0.053 1.00 45 260–285 10.00 50.00 1.0 1.0 0.928 0.091 0.543 0.053 1.00 45 285–300 11.67 58.35 1.0 1.0 0.882 0.086 0.516 0.051 1.00 45 300–357 12.50 62.50 1.0 1.0 0.862 0.085 0.504 0.049 1.00 45 Naithani et al. International Journal of Geo-Engineering (2022) 13:7 Page 8 of 12 For structural stability of heading portion of surge pool, rock support arrangements include 6  m long, 25  mm diameter fully cement grouted (Fe500) at 1500  mm  c/c stag- gered rock bolts and 150 mm thick steel fibre reinforced shotcrete (SFRS) in three layers were performed. Consolidation grouting using 45 mm dia. holes at 6 m c/c spacing and up to 6 m depth was also done. 7.0 m long and 50 mm diameter drain holes at 6.0 m c/c were also placed for controlling the underground seepage water if any in future (Fig. 2). Estimation of support system capacity Integrated approach given by Singh et  al. [20], Singh and Goel [21] and IS: 15026 [9] is used for the determination of surge pool crown support system capacity. Earlier this approach was used for the construction of underground caverns in the similar type of terrain [10–13]. The total support pressure (u + p ) will be equal to the sum of capaci- roof ties of support system executed at the crown portion Eq. (11): u + p = p + p + p sc gt roof bolt (11) where u = seepage water pressure = 0.0 t/m , p = roof support pressure (varying from roof 2 2 2 8.437 to 9.869 t/m ), p = capacity of SFRS (t/m ), p = capacity of rock bolts (t/m ), sc bolt p = capacity of grouted rock arch (t/m ). gt It is assumed that the SFRS is intimately in contact with the rock mass and having the tendency to fail by shearing and the capacity of SFRS is estimated as per Eq. (12). For the roof the capacity of SFRS estimated is 8.188 t/m . 2q × t fsc fsc p = fsc (12) BF fsc where p = support capacity of SFRS lining (t/m ), q = shear strength of SFRS (550 t/ sc fsc m ), t = thickness of SFRS, B = size of opening, F = mobilization factor for shotcrete fsc fsc (0.6 ± 0.05 – higher for cavern). The capacity of 6 m long, 25 mm diameter rock bolt is estimated as per Eq. (13) and the minimum capacity for surge pool roof calculated is 2.952 t/m . 2q × l sinθ crm p = (13) bolt BF 2 ′ where p = capacity of rock bolt (t/m ), q = UCS of reinforced rock mass, l = thick- crm bolt ness of reinforced rock arch/rock column, θ = 60; sin θ = 0.865, B = size of opening in m, F = mobilization factor for rock bolts. UCS of reinforced rock mass for the surge pool crown is calculated as per Eqs. (14) and (15) was 49.849 t/m . P 1 + sinϕ bolt q = − u × crm (14) 1 − sinϕ S j bolt tanϕ = j (15) a Thickness of reinforced rock arch Naithani  et al. International Journal of Geo-Engineering (2022) 13:7 Page 9 of 12 25 mm Ø, 6 m long, fully cement grouted rock bolts (Fe500) @ 1.5 m c/c spacing, Consolidation grouting Drain hole 50 mm Ø, 7 m 32-45 mm Ø, 6.0 m long @ 6 m c/c spacing deep @ 6 m c/c spacing Crown level 364.0 m 37.56 9.00 150 mm thick SFRS Spring level 355.0 m Maximum upsurge level 341.8 m 1.5 1.5 Typicallocationof drainage holes with respecttostaggered rock bolts for crown Rock bolts Minimum down surge 80.75 level 313.89 m Drainage holes Note:Rockbolts, grout holes and drainage holes are schematic 31.0 500 mm thick Scale concrete 0 m 4 m8 m 12 m Invert level 274.19 m Fig. 2 Support system of surge pool cavern Naithani et al. International Journal of Geo-Engineering (2022) 13:7 Page 10 of 12 where q = minimum uniaxial compressive strength of reinforced rock mass, crm P = capacity of bolt or tension in bolt (tones), S = spacing of bolt (1.5 m for roof ), bolt bolt u = seepage pressure in the rock mass (0.00 t/m ), J = Joint roughness number, J = Joint r a alteration number. Effective thickness of reinforced rock arch is calculated as per Eq. (16) and it is 4.775 m for surge pool crown: FAL S bolt l = l − − + S (16) rock arch 2 4 where l′ = effective thickness of reinforced rock arch, l = length of bolt (6 m), FAL = fixed anchor length (2.5  m), S = spacing of bolt (1.5  m), S = average spacing of joints bolt rock (0.400 m). Mobilization factor (F ) for the rock bolt is calculated as per Eq. (17). Singh et al. [20] proposed this equation after back analysis of Barton et al. [2] support systems case stud- ies. For the surge pool roof, F values are varying from 3.898 to 4.461: −0.35 F = 9.5 × p for rock anchor & full column grouted rock bolt s (17) roof where F = mobilization factor for rock bolt, p = roof support pressure. s roof The capacity of grouted rock arch is calculated by the Eq.  (18). The minimum and maximum grouted arch capacity for surge pool roof calculated is 4.289 t/m and 4.950 t/ m respectively. 2q × l gt gt p = gt (18) BF gt where p = support capacity of grouted arch (t/m ), q = UCS of grouted rock mass, gt gt l = thickness of grouted arch, B = size of opening, F = mobilization factor for grouted gt gt arch. For grouted arch, mobilization factor (F ) is calculated from Eq. (19). For surge pool gt roof F values are varying from 3.898 to 4.499. Total capacity of support system esti- gt mated for the entire portion of the heading portion of surge pool is given in Table 5. −0.35 F = 9.50 × p gt (19) roof Conclusions Heading portion of the surge pool was excavated using pilot and side slashing because size of the cavern is very large. 3D geological mapping of pilot is very important for pre- dicting geologic conditions up to bottom level and for side slashing. Rock mass charac- terization was done on the basis of geological logging data and in-situ testing. Support pressure estimation was based on tunnel quality index. 3D geological logging data was also used for recommendations of cavern support system and selecting supplemental rock bolt locations. For support design empirical approach was used which is backed by a systematic approach to rock mass classification. For structural stability the rock support arrangement includes steel fibre reinforced shotcrete, rock bolt, grouting and drainage hole provisions. Efficacy of support system is checked and results showed that Naithani  et al. International Journal of Geo-Engineering (2022) 13:7 Page 11 of 12 Table 5 Capacity of support system for roof Chainage (m) Ultimate Capacity of Capacity of Capacity of Total support capacity of 2 2 support SFRS (t/m ) rock bolt (t/ grouting (t/ support system (t/m ) 2 2 2 pressure (t/m ) m ) m ) 0.0–10 12.746 8.188 3.408 4.950 16.546 10–25 8.769 8.188 2.990 4.343 15.521 25–50 9.075 8.188 3.026 4.395 15.609 50–75 8.463 8.188 2.952 4.289 15.429 75–100 8.667 8.188 2.978 4.325 15.491 100–125 8.769 8.188 2.990 4.343 15.521 125–150 9.891 8.188 3.118 4.530 15.766 150–175 8.463 8.188 2.952 4.289 15.429 175–200 9.279 8.188 3.049 4.430 15.667 200–239 8.769 8.188 2.990 4.343 15.521 239–260 9.177 8.188 3.038 4.413 15.639 260–285 9.279 8.188 3.049 4.430 15.667 285–300 8.769 8.188 2.990 4.413 15.521 300–357 8.667 8.188 2.978 4.325 15.491 the estimated support system is adequate for crown. Minimum and maximum factor of safety estimated is 1.30 and 1.82 respectively while average factor of safety is 1.70. It is extrapolated that same rock types will be exposed during the benching of surge pool from El 355.00 to El 274.19 m and this data will be very helpful for the selection of meth- odology of benching down and selection of support system. It was recommended that real time engineering geological monitoring should be done during the benching down and accordingly support system should be modified. Real time engineering geological monitoring means as-and-when excavation is done, immediately 3D geological mapping should be done. Acknowledgements This paper is a part of sponsored project by M/s MEIL, so we sincerely thank the management of MEIL for the same. Authors are thankful to Dr. H.S. Venkatesh, Director NIRM for the permission to send the manuscript for publication, encouragement and technical guidance. Authors’ contribution LGS and DSR collected the data from the site, PJ finalize the figures and tables while AKN analize the data and finalize the manuscript. All authors read and approved the final manuscript. Funding This study was funded by Megha Engineering Infrastructure Development, under the Grant Number EG1802 to Ajay Kumar Naithani. Declarations Competing interests All authors declare that they have no competing interests. Received: 24 September 2020 Accepted: 21 January 2022 References 1. Anon (2017) Report on determination of in-situ stress parameters at the proposed underground surge pool of Palamuru Rangareddy lift irrigation scheme lift-II-pumping station. Unpubl. NIRM Report No. GE1704C 2. Barton N, Lien R, Lunde J (1974) Engineering classification of rock masses for the design of tunnel support. Rock Mech 6:189–236. https:// doi. org/ 10. 1007/ BF012 39496 Naithani et al. International Journal of Geo-Engineering (2022) 13:7 Page 12 of 12 3. 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Trans Tech Publication, Clausthal-Zellerfeld Publisher’s Note Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations. http://www.deepdyve.com/assets/images/DeepDyve-Logo-lg.png International Journal of Geo-Engineering Springer Journals

Engineering geological characteristics of the underground surge pool cavern: a case study, India

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anaithania@gmail.com National Institute of Rock For better rock mass characterization, 3D engineering geological mapping and in-situ Mechanics, Bengaluru, India testing was carried for the heading portion of surge pool of Palamuru Ranga Reddy lift irrigation scheme lift-II. The direction of the longest axis of the surge pool cavern was finalized based on the in-situ hydrofracturing testing inside the borehole and aligning the appurtenant structures of pump house and surge pool cavern on the ground. Rock types mapped were grey and pink granites belongs to the Peninsular Gneissic Complex of Archaean age. The assessment of Tunnel Quality Index ‘Q’ for the exposed granitic rock mass was done based on the information available of the rock joints and their nature, 3D geological mapping and in-situ stress measurement. The rock mass quality (Q) is related with the ultimate support pressure requirement. Excavation Support Ratio (ESR) as given in the ESR updated classification standard of NMT Q-system is applied to 1.0 for this cavern. On the basis of NMT Q-system chart and site geological characteris- tics, support system is recommended and its efficacy is assessed. Keywords: Engineering geology, Surge pool cavern, Support system, Rock bolt, Steel fibre reinforced shotcrete Introduction 357.00  m long, 89.81  m high and 31.00  m wide underground surge pool cavern for a lift irrigation scheme is being constructed in the part of Telangana State of India. The main design approaches for underground cavern excavation in rock are analytical, observational, and empirical. In this paper empirical approach for support design of underground surge pool cavern of a Palamuru Ranga Reddy lift irrigation scheme lift- II (PRLIS-L-II) is discussed. Rock mass classifications as practiced in civil and mining engineering works form an integral part of the empirical design methods, which is the most predominant design approach [4]. The main objectives of the rock mass classifica - tions are to identify the most significant parameters influencing the behavior of a rock mass, divide area into rock mass classes of varying quality and provide quantitative data for engineering design purpose. Empirical approaches are developed for the stability of underground structures based on the large number of case studies. © The Author(s) 2022. Open Access This article is licensed under a Creative Commons Attribution 4.0 International License, which permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons licence, and indicate if changes were made. The images or other third party material in this article are included in the article’s Creative Commons licence, unless indicated otherwise in a credit line to the mate- rial. If material is not included in the article’s Creative Commons licence and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder. To view a copy of this licence, visit http:// creat iveco mmons. org/ licen ses/ by/4. 0/. Naithani et al. International Journal of Geo-Engineering (2022) 13:7 Page 2 of 12 Table 1 Summary of input data 1. Length of surge pool 357.00 m 9. Rise of arc 9.00 m 2. Excavated width of cavern (B) 31.00 m 10. Bottom floor level 274.19 m 3. Height of surge pool 89.81 m 11. Minimum down surge level 313.89 m 4. Height of surge pool walls 80.81 m 12. Maximum upsurge level 341.80 m 5. Crown level 364.00 m 13. Service bay level 346.0 m 6. Spring level 355.00 m 14. Vertical stress (σ ) 3.44 MPa 7. Height of overburden above 67.48 m (average) 15. Maximum horizontal principal 5.46 ± 1.23 MPa crown (H) stress (σ ) 8. Ground levels 431.48 m 16. Minimum horizontal principal 3.64 ± 0.82 MPa stress (σ ) Fig. 1 3D view of pump house complex including surge pool and pump house For surge pool cavern of PRLIS lift-II, rock mass characterization was done based on 3D geologic mapping and in-situ stress measurement. For the orientation of the long axis of the surge pool underground cavern, hydrofrac test inside the NX bore- hole BH-01 was carried out by NIRM. Vertical borehole (BH-01) of 130 m depth was drilled from the surface. From this test, magnitudes of the principal stresses as well as the direction of maximum horizontal principal stress were determined. After detailed analysis it was concluded that the K-value (σ /σ = 1.58) indicates a medium stress H v magnitude and the maximum horizontal principal stress direction N30°, which was recommended for the orientation of the long axis of the cavity to reduce ground con- trol problems [1]. For this cavern the vertical cover is more than 67 m and summary of input data used for the recommendation of support system for underground surge pool cavern is given in Table  1 and 3D view of pump house complex including surge pool and pump house is given in Fig. 1. Naithani  et al. International Journal of Geo-Engineering (2022) 13:7 Page 3 of 12 Site geological condition Surge pool site of Palamuru Ranga Reddy lift irrigation scheme lift-II forms a part of the Peninsular Shield of the Indian Sub-continent [16]. The site forms a part of Eastern Block of Dharwar Craton mainly comprised of Archaean granites which are intruded by mafic dykes age ranging from Archaean to Upper Proterozoic [18]. Gran - ites and gneisses are exposed in and around the surge pool area. Granites and gneisses have deformational history documenting three phases of folding [7, 16]. Granites and gneisses are intruded by different types of younger granites [17]. The surge pool area exhibits a gently undulated topography with isolated hillocks and undulated hilly terrain with intermittent broad valley portions. On the surface along the surge pool alignment medium to coarse grained pink/grey granites were exposed. 3D engineering geological mapping of the heading portion of surge pool cavern was carried out in 1:100 scale. This will be a permanent record of all geologic defects pre - sent in the excavated portion. After proper cleaning and scaling, in adequate lighting geological logging was done. Rock types mapped after the excavation were grey and pink granite belongs to the Peninsular Gneissic Complex of Archaean age [15, 16]. Granites were medium to coarse grained, hard, jointed and fresh in nature. The rock mass was characterized by generally two plus random joint sets, which were generally more than 15 m in persistent, slightly rough, rough undulating, rough planar to smooth planar, with unaltered joint walls (Table  2). Minor staining has been recorded along some joint surfaces. Joints were moderately to widely spaced in nature. The rock mass was characterized by dry condition. Minor cracks/fractures developed due to blasting were also recorded. About 20  cm wide dolerite dyke was recorded towards right side edge, where the granite rock mass was sheared at the contact with the dyke. Dolerite dyke was fresh, hard and compact in nature. However, the contact zones of dolerite and the adjoin- ing granite were slightly sheared. Along the contact zones i.e., over a width of 0.40 m, welded wire mesh was placed and 50  mm extra SFRS layer was put to prevent any rock fall during benching down. Table 2 Joint sets recorded in pink/grey granite Joint sets Azimuth/ Spacing Strike Roughness Aperture Infilling Ground dip amount (cm) length (m) (mm) water J1 280–310/V 20–60 > 20 Slightly Tight to 1 Fresh/ Dry rough, stained smooth planar J2 220/10–15 30–40 10–20 Slightly Tight to 1 Fresh/ Dry rough, stained smooth planar J3 220/V 20–70 > 20 Rough undu- Tight to 1 Fresh/ Dry lating stained J4 130/60–65 30–40 > 15 Smooth Tight to 1 Fresh/ Dry planar stained J5 30–50/V 20–70 > 20 Rough Tight Fresh Dry planar Naithani et al. International Journal of Geo-Engineering (2022) 13:7 Page 4 of 12 Rock mass classification The rock mass of the heading portion of surge pool cavern was classified based on tun - nelling quality index (Q). Based on six parameters i.e. rock quality designation (RQD), number of joint sets (J ), joint roughness number (J ), joint alteration number (J ), joint n r a water reduction factor (J ) and stress reduction factor (SRF), the Q-values are calculated using the Eq. (1) [2, 5, 6]. High Q-values means good stability while low Q-values indi- cates poor stability. World-wide this classification is being used for the characterization of rock mass of an underground opening in jointed rock masses. RQD J J r w Q = + + (1) J J SRF n a All the parameters were determined during geological mapping using tables that give numerical values to be assigned to a described situation. All the discontinuities per 5 m length were taken into consideration for the calculation of Q-values and in general two plus random (R) joint sets were intersecting at 5 m length and circumference. RQD val- ues were ranging from 60 to 80% and average RQD value was 70%. Total excavation was done in dry condition. The assessment of Q-values based on the information available of the rock joints and their nature and 3D geological logging, is tabulated in Table 3. Roof support pressure, wall support pressure and ground squeezing condition were estimated based on Q-values. The grade of rock mass based on the rock joints characteristics has the Q-values varying from 3.89 to 13.33, and it comes under poor to good rock mass category. The average Q-value calculated is 10.87. The poor Q-value was estimated at the intersection portion only. Estimation of support pressure and ground squeezing condition Barton et  al. [2] gives an empirical equation relating rock mass quality ‘Q’ and perma- nent support pressure based on the case records Eq.  (2). They also give an improved empirical fit by incorporating separate weighting for the number of joint sets (J ) Eq. (3). For the surge pool cavern of PRLIS lift-II, roof support and wall support pressures are estimated as per Eqs. (4) and (5), which are applicable for the non-squeezing ground condition [8, 19]. 2.0 −1/3 P = Q roof (2) 1/2 −1/3 2J (Q) P = (3) roof 3J 2.0 −1/3 P = Q × f roof (4) 2.0 −1/3 P = Q × f Wall (5) r Naithani  et al. International Journal of Geo-Engineering (2022) 13:7 Page 5 of 12 Table 3 Q-values recorded from the heading portion of the surge pool Chainage Rock type Rock quality Number Joint Joint Joint water Stress Q (m) designation of joint roughness alteration reduction reduction Value Class (%) sets number number factor factor 0–10 Medium 70 2 + R Smooth, Unaltered Dry excava- Medium 3.89 Poor to coarse (intersec- planar tion stress granite tion) 10–25 Medium 70 2 + R Smooth, Unaltered, Dry excava- Medium 11.67 Good to coarse planar stained tion stress granite 25–50 Medium 65 2 + R Smooth, Unaltered Dry excava- Medium 10.83 Good to coarse planar tion stress granite 50–75 Medium 80 2 + R Smooth, Unaltered Dry excava- Medium 13.33 Good to coarse planar tion stress granite 75–100 Medium 75 2 + R Smooth, Unaltered, Dry excava- Medium 12.50 Good to coarse planar stained tion stress granite 100–125 Medium 70 2 + R Smooth, Unaltered, Dry excava- Medium 11.66 Good to coarse planar stained tion stress granite 125–150 Medium 75 3 Smooth, Unaltered Dry excava- Medium 8.33 Fair to coarse planar tion stress granite 150–175 Medium 80 2 + R Smooth, Unaltered, Dry excava- Medium 13.33 Good to coarse planar stained tion stress granite 175–200 Medium 60 2 + R Smooth, Unaltered Dry excava- Medium 10.00 Good to coarse planar tion stress granite 200–239 Medium 70 2 + R Smooth, Unaltered, Dry excava- Medium 11.67 Good to coarse planar stained tion stress granite 239–260 Medium 65 2 + R Smooth, Unaltered, Dry excava- Medium 10.83 Good to coarse planar stained tion stress granite 260–285 Medium 60 2 + R Smooth, Unaltered Dry excava- Medium 10.00 Good to coarse planar tion stress granite 285–300 Medium 70 2 + R Smooth, Unaltered, Dry excava- Medium 11.67 Good to coarse planar stained tion stress granite 300–357 Medium 75 2 + R Smooth, Unaltered Dry excava- Medium 12.50 Good to coarse planar tion stress granite where P is permanent/ultimate roof support pressure in kg/cm , P is ultimate wall roof wall support pressure in kg/cm , Jr is joint roughness number, Q is rock mass quality, Q is wall quality/factor equal to 2.5Q for intermediate qualities (0.1 < Q < 10) and 5Q for good qualities (Q > 10) in case of medium stress, J is joint set number and f is correction factor for overburden. Correction factor for overburden can be estimated from Eq. (6), where ‘H’ is the height of overburden above crown in metres. (H − 320) (67.48 − 320) f = 1 + ≥ 1 = 1 + = 0.68 (6) 800 800 For the estimation of non-squeezing ground condition Singh et al. [19] suggested an empirical approach Eq. (7) based on case histories and by collecting Barton et al. [2] Naithani et al. International Journal of Geo-Engineering (2022) 13:7 Page 6 of 12 ‘Q’ data and overburden (H). Minimum Q-value is used for the estimation of ground squeezing condition. Ground condition is non-squeezing because above surge pool cavern, cover is 67.48  m only. The required support pressure for crown is varying 2 2 between 8.437 and 9.869 t/m and for walls 4.934–7.271 t/m (Table  4). The average 2 2 support pressure for crown is 8.927 t/m and for walls 5.336 t/m . 1/3 1/3 H < 350Q ; 67.48 < 350 × 8.33 = 709 (7) Rock support As per hydraulic design, the surge pool of lift-II scheme is having an excavated width of 31.00 m and length 357.00 m. The crown level of surge pool is kept at EL 364.00 m and bottom level at EL 274.19  m. As per hydraulic design, the maximum upsurge level of surge pool works out to EL 341.80  m and minimum down surge level works out to EL 313.89 m. Surge pool with 500 mm thick concrete lined in the lower portion is proposed. For the heading portion of surge pool cavern reinforcement support pattern using Nor- wegian Method of Tunnelling (NMT) Q-system was used. Excavation Support Ratio (ESR) of cavity as given in the ESR updated classification standard of NMT Q-system is applied to 1.0 [14]. The Equivalent Dimension (De) is applied by dividing the span (m) of surge pool cavern by the fore-mentioned ESR. Bolt length which is depend on excavation dimension can be estimated from the excavation span (B) and the excava- tion support ratio (ESR) [2, 3] Eq. (8). By applying this formula, the length of rock bolt for the crown is calculated to be 6.65 m. The value of NMT Q-system chart proposed is 7.0–8.0 m for the crown: 0.15B L = 2 + (8) roof ESR where L is bolt length in metres for roof, B is span in metres and ESR is the excavation roof support ratio. The Norwegian Institute for Rock Blasting Technique has proposed a formula Eq. (9) to estimate the length of the bolts in the central section of the opening where ‘B’ is the span of the opening in metres [22]. By applying this, the length of rock bolt for crown of surge pool is calculated to be 7.10 m Eq. (9). L = 1.40 + 0.184 B (9) The thickness of steel fibre reinforced shotcrete (t ) can be estimated from the ulti- fsc mate support pressure (P ), size of opening (B), mobilization factor for shotcrete roof (F   −  0.6 ± 0.05) and shear strength of steel fibre reinforced shotcrete (q   –  550  t/ fsc fsc m ) as per Eq. (10) [9]. The thickness of SFRS for crown is calculated from the average Q-value to be 150  mm. The value of NMT Q-system chart proposed is 70–90  mm for crown. P × B × F roof fsc t = fsc (10) 2q fsc Naithani  et al. International Journal of Geo-Engineering (2022) 13:7 Page 7 of 12 Table 4 Support pressure for the roof and walls of surge pool cavern Chainage (m) Q value for roof Q value for wall Joint roughness Joint alteration Ultimate roof support Ultimate wall support Jr/Ja Friction angle −1 number for crown & number for crown & pressure pressure φ = tan (J /J ) j r a wall wall 2 2 (kg/cm ) MPa (kg/cm ) MPa 0.0–10 3.89 9.73 1.0 1.0 1.272 0.125 0.937 0.092 1.00 45 10–25 11.67 58.35 1.0 1.0 0.882 0.086 0.516 0.051 1.00 45 25–50 10.83 54.15 1.0 1.0 0.904 0.089 0.529 0.052 1.00 45 50–75 13.33 66.65 1.0 1.0 0.844 0.083 0.493 0.048 1.00 45 75–100 12.50 62.50 1.0 1.0 0.862 0.085 0.504 0.049 1.00 45 100–125 11.66 58.30 1.0 1.0 0.882 0.086 0.516 0.051 1.00 45 125–150 8.33 20.83 1.0 1.0 0.987 0.097 0.727 0.071 1.00 45 150–175 13.33 66.65 1.0 1.0 0.844 0.083 0.493 0.048 1.00 45 175–200 10.00 50.00 1.0 1.0 0.928 0.091 0.543 0.053 1.00 45 200–239 11.67 58.35 1.0 1.0 0.882 0.086 0.516 0.051 1.00 45 239–260 10.38 51.90 1.0 1.0 0.917 0.090 0.536 0.053 1.00 45 260–285 10.00 50.00 1.0 1.0 0.928 0.091 0.543 0.053 1.00 45 285–300 11.67 58.35 1.0 1.0 0.882 0.086 0.516 0.051 1.00 45 300–357 12.50 62.50 1.0 1.0 0.862 0.085 0.504 0.049 1.00 45 Naithani et al. International Journal of Geo-Engineering (2022) 13:7 Page 8 of 12 For structural stability of heading portion of surge pool, rock support arrangements include 6  m long, 25  mm diameter fully cement grouted (Fe500) at 1500  mm  c/c stag- gered rock bolts and 150 mm thick steel fibre reinforced shotcrete (SFRS) in three layers were performed. Consolidation grouting using 45 mm dia. holes at 6 m c/c spacing and up to 6 m depth was also done. 7.0 m long and 50 mm diameter drain holes at 6.0 m c/c were also placed for controlling the underground seepage water if any in future (Fig. 2). Estimation of support system capacity Integrated approach given by Singh et  al. [20], Singh and Goel [21] and IS: 15026 [9] is used for the determination of surge pool crown support system capacity. Earlier this approach was used for the construction of underground caverns in the similar type of terrain [10–13]. The total support pressure (u + p ) will be equal to the sum of capaci- roof ties of support system executed at the crown portion Eq. (11): u + p = p + p + p sc gt roof bolt (11) where u = seepage water pressure = 0.0 t/m , p = roof support pressure (varying from roof 2 2 2 8.437 to 9.869 t/m ), p = capacity of SFRS (t/m ), p = capacity of rock bolts (t/m ), sc bolt p = capacity of grouted rock arch (t/m ). gt It is assumed that the SFRS is intimately in contact with the rock mass and having the tendency to fail by shearing and the capacity of SFRS is estimated as per Eq. (12). For the roof the capacity of SFRS estimated is 8.188 t/m . 2q × t fsc fsc p = fsc (12) BF fsc where p = support capacity of SFRS lining (t/m ), q = shear strength of SFRS (550 t/ sc fsc m ), t = thickness of SFRS, B = size of opening, F = mobilization factor for shotcrete fsc fsc (0.6 ± 0.05 – higher for cavern). The capacity of 6 m long, 25 mm diameter rock bolt is estimated as per Eq. (13) and the minimum capacity for surge pool roof calculated is 2.952 t/m . 2q × l sinθ crm p = (13) bolt BF 2 ′ where p = capacity of rock bolt (t/m ), q = UCS of reinforced rock mass, l = thick- crm bolt ness of reinforced rock arch/rock column, θ = 60; sin θ = 0.865, B = size of opening in m, F = mobilization factor for rock bolts. UCS of reinforced rock mass for the surge pool crown is calculated as per Eqs. (14) and (15) was 49.849 t/m . P 1 + sinϕ bolt q = − u × crm (14) 1 − sinϕ S j bolt tanϕ = j (15) a Thickness of reinforced rock arch Naithani  et al. International Journal of Geo-Engineering (2022) 13:7 Page 9 of 12 25 mm Ø, 6 m long, fully cement grouted rock bolts (Fe500) @ 1.5 m c/c spacing, Consolidation grouting Drain hole 50 mm Ø, 7 m 32-45 mm Ø, 6.0 m long @ 6 m c/c spacing deep @ 6 m c/c spacing Crown level 364.0 m 37.56 9.00 150 mm thick SFRS Spring level 355.0 m Maximum upsurge level 341.8 m 1.5 1.5 Typicallocationof drainage holes with respecttostaggered rock bolts for crown Rock bolts Minimum down surge 80.75 level 313.89 m Drainage holes Note:Rockbolts, grout holes and drainage holes are schematic 31.0 500 mm thick Scale concrete 0 m 4 m8 m 12 m Invert level 274.19 m Fig. 2 Support system of surge pool cavern Naithani et al. International Journal of Geo-Engineering (2022) 13:7 Page 10 of 12 where q = minimum uniaxial compressive strength of reinforced rock mass, crm P = capacity of bolt or tension in bolt (tones), S = spacing of bolt (1.5 m for roof ), bolt bolt u = seepage pressure in the rock mass (0.00 t/m ), J = Joint roughness number, J = Joint r a alteration number. Effective thickness of reinforced rock arch is calculated as per Eq. (16) and it is 4.775 m for surge pool crown: FAL S bolt l = l − − + S (16) rock arch 2 4 where l′ = effective thickness of reinforced rock arch, l = length of bolt (6 m), FAL = fixed anchor length (2.5  m), S = spacing of bolt (1.5  m), S = average spacing of joints bolt rock (0.400 m). Mobilization factor (F ) for the rock bolt is calculated as per Eq. (17). Singh et al. [20] proposed this equation after back analysis of Barton et al. [2] support systems case stud- ies. For the surge pool roof, F values are varying from 3.898 to 4.461: −0.35 F = 9.5 × p for rock anchor & full column grouted rock bolt s (17) roof where F = mobilization factor for rock bolt, p = roof support pressure. s roof The capacity of grouted rock arch is calculated by the Eq.  (18). The minimum and maximum grouted arch capacity for surge pool roof calculated is 4.289 t/m and 4.950 t/ m respectively. 2q × l gt gt p = gt (18) BF gt where p = support capacity of grouted arch (t/m ), q = UCS of grouted rock mass, gt gt l = thickness of grouted arch, B = size of opening, F = mobilization factor for grouted gt gt arch. For grouted arch, mobilization factor (F ) is calculated from Eq. (19). For surge pool gt roof F values are varying from 3.898 to 4.499. Total capacity of support system esti- gt mated for the entire portion of the heading portion of surge pool is given in Table 5. −0.35 F = 9.50 × p gt (19) roof Conclusions Heading portion of the surge pool was excavated using pilot and side slashing because size of the cavern is very large. 3D geological mapping of pilot is very important for pre- dicting geologic conditions up to bottom level and for side slashing. Rock mass charac- terization was done on the basis of geological logging data and in-situ testing. Support pressure estimation was based on tunnel quality index. 3D geological logging data was also used for recommendations of cavern support system and selecting supplemental rock bolt locations. For support design empirical approach was used which is backed by a systematic approach to rock mass classification. For structural stability the rock support arrangement includes steel fibre reinforced shotcrete, rock bolt, grouting and drainage hole provisions. Efficacy of support system is checked and results showed that Naithani  et al. International Journal of Geo-Engineering (2022) 13:7 Page 11 of 12 Table 5 Capacity of support system for roof Chainage (m) Ultimate Capacity of Capacity of Capacity of Total support capacity of 2 2 support SFRS (t/m ) rock bolt (t/ grouting (t/ support system (t/m ) 2 2 2 pressure (t/m ) m ) m ) 0.0–10 12.746 8.188 3.408 4.950 16.546 10–25 8.769 8.188 2.990 4.343 15.521 25–50 9.075 8.188 3.026 4.395 15.609 50–75 8.463 8.188 2.952 4.289 15.429 75–100 8.667 8.188 2.978 4.325 15.491 100–125 8.769 8.188 2.990 4.343 15.521 125–150 9.891 8.188 3.118 4.530 15.766 150–175 8.463 8.188 2.952 4.289 15.429 175–200 9.279 8.188 3.049 4.430 15.667 200–239 8.769 8.188 2.990 4.343 15.521 239–260 9.177 8.188 3.038 4.413 15.639 260–285 9.279 8.188 3.049 4.430 15.667 285–300 8.769 8.188 2.990 4.413 15.521 300–357 8.667 8.188 2.978 4.325 15.491 the estimated support system is adequate for crown. Minimum and maximum factor of safety estimated is 1.30 and 1.82 respectively while average factor of safety is 1.70. It is extrapolated that same rock types will be exposed during the benching of surge pool from El 355.00 to El 274.19 m and this data will be very helpful for the selection of meth- odology of benching down and selection of support system. It was recommended that real time engineering geological monitoring should be done during the benching down and accordingly support system should be modified. Real time engineering geological monitoring means as-and-when excavation is done, immediately 3D geological mapping should be done. Acknowledgements This paper is a part of sponsored project by M/s MEIL, so we sincerely thank the management of MEIL for the same. Authors are thankful to Dr. H.S. Venkatesh, Director NIRM for the permission to send the manuscript for publication, encouragement and technical guidance. Authors’ contribution LGS and DSR collected the data from the site, PJ finalize the figures and tables while AKN analize the data and finalize the manuscript. All authors read and approved the final manuscript. Funding This study was funded by Megha Engineering Infrastructure Development, under the Grant Number EG1802 to Ajay Kumar Naithani. Declarations Competing interests All authors declare that they have no competing interests. Received: 24 September 2020 Accepted: 21 January 2022 References 1. Anon (2017) Report on determination of in-situ stress parameters at the proposed underground surge pool of Palamuru Rangareddy lift irrigation scheme lift-II-pumping station. Unpubl. NIRM Report No. GE1704C 2. Barton N, Lien R, Lunde J (1974) Engineering classification of rock masses for the design of tunnel support. Rock Mech 6:189–236. https:// doi. org/ 10. 1007/ BF012 39496 Naithani et al. International Journal of Geo-Engineering (2022) 13:7 Page 12 of 12 3. 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Journal

International Journal of Geo-EngineeringSpringer Journals

Published: Dec 1, 2022

Keywords: Engineering geology; Surge pool cavern; Support system; Rock bolt; Steel fibre reinforced shotcrete

References