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hari.chennarapu@mah- indrauniversity.edu.in The infrastructure plays a vital role in stimulating economic growth. Any infra project Ecole Centrale School requires proper planning, design, construction, quality control (QC), and quality assess- of Engineering, Mahindra University, Bahadurpally, ment (QA). It is important to comply with QC and QA to avoid failure and enhance Jeedimetla, Hyderabad, the long-term pavement performance in order to provide a safe and solid system of Telangana 500043, India transportation. Researchers were replacing laborious and time-consuming density- Full list of author information is available at the end of the article based methods (sand cone and/or core cutter) with advanced stiffness or modulus- based NDT devices for the QC of compacted geomaterials. The lightweight deflectom- eter (LWD) is such a highly advanced and sophisticated device that was developed to evaluate the deformation modulus (E ) of compacted geomaterials as an alternative LWD of density test. This device is portable, light-weight, user-friendly, and it is ideally suit- able for all constructional geomaterials. This study is intended to provide a state-of- the-art on the LWD device as well as presented the ranges of deformation modulus for various geomaterials from several studies. For instance, in the case of soils, aggregates, and asphalt materials deformation modulus values were found to be in the range of 35–60 MPa, 80–120 MPa, and 120–170 MPa respectively. In addition, several studies have been compiled to completely comprehend the relationship between LWD and various devices. Keywords: Quality control (QC), Compacted geomaterials, Lightweight deflectometer (LWD), Deformation modulus (E ) LWD Introduction Road networks are one of the key components for the economic growth of any devel- oped nation. The Ministry of Road Transport and Highways  proposes to develop var - ious mega projects by connecting expressways/access-controlled/strategic, coastal and port connectivity highways, economic corridors, and border roads. Quality control and Quality Assurance (QC and QA) are the important criteria in order to ensure quality of construction, minimal maintenance, and long-term performance of pavements. The required degree of compaction needs to be achieved by controlling the process of geo- materials compaction in the field. Typically, this process involves the use of periodic in- situ monitoring of density and moisture, generally obtained by using destructive tests © The Author(s) 2022. 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Duddu and Chennarapu International Journal of Geo-Engineering (2022) 13:6 Page 2 of 13 such as sand cone test, core cutter test and rubber balloon test as well as non-destructive tests (NDT) such as Moisture Density Indicator (MDI) and Electrical Density Gauge (EDG) which are tedious, time-consuming, laborious and sometimes not feasible to perform in accordance with the specifications, whereas Nuclear Density Gauge (NDG) releases gamma radiation, which causes a potential hazard to the user and frequency response of the Soil Density Gauge (SDG) will be influenced by the soil gradation (refer Table 1). Hence, the importance and usage of non-destructive test (NDT) devices based on stiffness/modulus has been increased and the success rate is in the range of 64–86%, compared to the density-based devices . The Stiffness/modulus-based NDT devices are Briaud Compaction Device (BCD), Clegg Hammer (CH), Dynamic Cone Penetrometer (DCP), and Soil Stiffness Geo- Gauge (SSGG). In addition, various deflectometer devices are available for measuring the deformation modulus of the compacted geomaterials. Those are, dropping weight deflectometer (DWD), Heavyweight deflectometer (HWD), Falling weight deflectometer (FWD), Rolling weight deflectometer (RWD), and Lightweight deflectometer (LWD). According to Ebrahimi and Edil , the usage of lightweight deflectometer (LWD) has been increased to evaluate the quality of any compacted geomaterial for its ease of use, portability, without interrupting the construction activities and suitable for all types of geomaterials. In 1981, a portable dropping weight deflectometer (DWD) was first invented and developed by the Federal Highway Research Institute (FHRI) and Headquarters of Magdeburger Prufgeratebau (HMP) Company . However, research within European countries has been focused on demonstrating the usefulness and reliability through field trials. The LWD currently uses technology that is similar to trailer mounted-FWD equipment, with the reduced load pulse duration and reduced maximum applied force being the first compromise in the development of the LWD device to convert into porta - bility. An extensive study has been carried out using the LWD device on pavement struc- tures for QC for the past three decades. The utilization of LWD device is more reliable as it provides consistent correlation and measurements . A general comparison of con- ventional in-situ density-based devices and stiffness/modulus-based devices are listed in Tables 1 and 2 respectively. A detailed description of the LWD operating principles, strengths and limitations, has been reported in the literature [6–9]. The main focus of this study is to present the various research works carried out by using the LWD device. Description of LWD device and operating procedure Figure 1 shows the schematic view of LWD device with the components. The major components of the LWD device are drop weight, loading plate, and accelerometer. Initially, place the loading plate on top of the compacted geomaterials, release the drop weight along the guide rod by ensuring a standard drop height. The drop weight is allowed to drop on buffers made of either rubber pads or steel springs and deforma - tion of the loading plate is measured with the help of an accelerometer. The first three drops are allowed for seating to enhance the intact contact between the loading plate and compacted geomaterials. The next three consecutive drops are used to evaluate the average deformation. Finally, the deformation modulus (E ) can be calculated LWD D uddu and Chennarapu International Journal of Geo-Engineering (2022) 13:6 Page 3 of 13 Table 1 Comparison of in-situ density-based devices Function SCT CCT RBT NDG MDI EDG SDG Mode of measurement Physically Physically Physically Gamma radiation Electro-magnetic wave High radio frequency Electro-magnetic imped- ance spectroscopy Standards ASTM D1556 Not applicable ASTM D2167 ASTM D6938 ASTM D6780 ASTM D7698 ASTM D7830 Final output γ γ γ γ and W γ and W γ and W γ and W d d d d d d d Calibration Not applicable Not applicable Not applicable Required Lab test in Proctor Mould Field calibration required Field calibration required Portability No No No Yes No No Yes Durability Good Medium Medium Good Good Good Good Operator skill and training Moderate and not Moderate and not Moderate and required Extensive and licensed Moderate and required Moderate and required Extensive and required required required Operating Easy Easy Easy Difficult Difficult Difficult Difficult Destructive Yes Yes Yes No No No No Storing data No No No Yes Yes Yes Yes GPS No No No Yes No Yes Yes Man power 2 2 1 1 2 2 1 Merits Easy to operate Easy to operate Accurate and reliable Relatively speed to Operator dependency Does not require any spe- Accurate and repeatable perform cial license to operate Long history of accept- Long history of accept- Long history of accept- Accurate and repeatable Safer compare to NDG ancy ancy ancy Low cost Low cost Low cost Able to vary depth of measurement De-Merits Tedious and Time-con- Tedious and Time-con- Tedious and Time-con- Gamma radiation may Complex and time- Complex and time- Necessary corrections need suming suming suming represent potential hazard consuming consuming to apply Pause operation Pause operation Balloon membranes can Safety concerns require Cumbersome in operat- Cumbersome in operat- Results are not reliable, puncture during testing monitoring of personnel ing ing because soil gradation by dosimeter badges affects the frequency response Excavated material needs Excavated material needs Excavated material needs – Cannot be used to test Difficult to drive probes – to be recovered carefully to be recovered carefully to be recovered carefully frozen soils into stiff soils SCT sand cone test, CCT core cutter test, RBT rubber balloon test, NDG nuclear density gauge, MDI moisture density indicator, EDG electrical density gauge, SDG soil density gauge Duddu and Chennarapu International Journal of Geo-Engineering (2022) 13:6 Page 4 of 13 Table 2 Comparison of in-situ stiffness/modulus-based devices Function BCD CH DCP SGG LWD Mode of meas- Strain gauges Accelerometer Physically Velocity (small Geophone or urement dynamic force- accelerometer frequency) Standards None ASTM D5874 ASTM D6951 ASTM D6758 ASTM E 2583 Final output Modulus CIV DPI Modulus Deformation modulus Moisture read- No Yes No No No ing Calibration of BCD test on rub- Lab test in proc- None Calibration plate Required device ber blocks tor mould Portability Yes Yes Yes Yes Yes Durability NA Good Good Good Good Operator skill Low and moder- Low and moder- Low and moder- Moderate and Low and Moder- and training ate ate ate high ate Operating Easy Moderate Easy Easy Easy Destructive No No Low No No Storing data Yes Yes No Yes Yes GPS No Yes No Yes Yes Man power 1 2 2 1 1 Merits Quick Quick Assess up to Quick and non- Very quick 1.2 m thick layer intrusive Strong correla- Strong cor- Suitable for all tions with CBR relation with CBR materials and M De-merits Not suitable for Boundary effects Maximum Extremely sensi- High variability in very stiff or soft during calibra- allowed particle tive to seating weak soft soils soil tion size is 50 mm conditions Different CIV for Slow test Inconsistencies Shallow Influence CH models in testing data depth BCD briaud compaction device, CH clegg hammer, DCP dynamic cone penetration, SSGG soil stiffness geo ‑ gauge, LWD lightweight deflectometer, CIV clegg impact value, DPI dynamic cone penetration index, CBR California bearing ratio, E LWD deformation modulus, M resilient modulus by using the well-known Boussinesq’s elastic solution (Eq. 1) for the case of a rigid or flexible base resting on an elastic half-space. Table 3 presents various LWD devices and specifications which were manufactured by various agencies. qr(1 − υ )f E = (1) LWD where E = Deformation modulus of compacted geomaterial (MPa), r = Radius of LWD loading plate (mm), υ = Poisson’s ratio of the compacted geomaterial, f = Plate rigidity factor (Fig. 3), w = Deformation of the loading plate measured at its center (mm), and q = Maximum contact pressure (MPa); where; AppliedForce(F) q = (2) Areaoﬂoadingplate(a) F = Applied force (N) and a = area of loading plate (mm ). D uddu and Chennarapu International Journal of Geo-Engineering (2022) 13:6 Page 5 of 13 Handle Drop weight fix and release mechanism Adjustable drop height (Max. 72 cm) Guiding rod Drop weight (10 kg) Buffer (Steel spring) Sensor (Accelerometer) Load cell (7.07 kN) Handle for shifting Loading plate (100,150 or 300) mm Fig. 1 Schematic view of Lightweight Deflectometer (LWD) Table 3 Summary of specifications of the LWD devices. (Modified after ) Description/ Zorn Keros Dynatest Prima Loadman ELE TFT CSM devices Plate type Solid Annulus Annulus Annulus Solid Solid Annulus Solid Plate diam- 100, 150, 150, 200, 100, 150, 100, 200, 110, 130, 300 200, 300 200, 300 eter (mm) 200, 300 300 200, 300 300 200, 300 Plate thick- 45, 28, 20 20 20 20 Not Not Not Not ness (mm) reported reported reported reported a a a Plate mass 15 Not Not 12 6 Not Variable 6.8, 8.3 (kg) reported reported reported Drop mass 10, 15 10, 15, 20 10, 15, 20 10, 15, 20 10 10 10, 15, 20 10 (kg) Drop height 720 Variable Variable Variable 800 Variable Variable Variable (mm) Buffer type Steel Rubber Rubber Rubber Rubber Not Rubber Urethane springs (conical) (flat) (conical) reported Force display No Yes Yes Yes Yes Not Yes Yes reported Transducer Accelero- Geo- Geo- Geo- Accelero- Geo- Geo- Geophone type meter phone phone phone meter phone phone Transducer Plate Ground Ground Ground Plate Plate Ground Plate location Impulse time 18 ± 2 15–30 15–30 15–20 25–30 Not 15–25 15–25 (ms) reported b b b b b b b Max load(kN) 7.07 15.0 15.0 15.0 20 10 15 8.8 Plate rigidity Uniform Rigid/flex - Rigid/flex - User Rigid/flex - User User User ible ible defined ible defined defined defined May varies based on plate thickness May varies based on drop height Duddu and Chennarapu International Journal of Geo-Engineering (2022) 13:6 Page 6 of 13 Theoretically, the applied force on a surface cannot be constant, because it clearly depends on the stiffness of the buffer material on which the load is applied (Eq. 3): F = 2mghc (3) where; F = Applied force (N), m = mass of falling weight (kg), g = acceleration due to gravity, 9.81 (m/s ), h = drop height (m), and c = material stiffness constant (N/m). Factors influencing the deformation modulus Various parameters that influence the deformation modulus of compacted geomaterials are diameter of loading plate, plate rigidity, plate contact stress, loading rate, buffer type, loca - tion, and type of deformation transducer [7, 9]. Further details on the various factors influ - encing the deformation modulus (E ) are discussed in the following sections. LWD Diameter of loading plate The diameter of loading plate is in the range of 100–300 mm (refer Table 3). Research- ers (Deng-Fong Lin et al., Chaddock and Brown [6, 10]) concluded that the selection of the diameter of loading plate is a significant factor that influences deformation modu - lus due to the reason of depth of influence. Generally, the depth of influence is equal to 1.0–1.5 times the diameter of the loading plate. In the literature, it is reported that the decrease in diameter of the loading plate leads to an increase in the deformation modulus, due to the reason of increase in contact stresses of loading plate. Chaddock and Brown  conducted tests on crushed rock base and subbase materials over compacted clay materials. The deformation modulus for the 200 mm diameter loading plate was found to be 1.3–1.5 times that of a 300 mm diameter loading plate. Deng- Fong Lin et al. , performed field studies using the LWD device on a natural sand soil deposit and found that the estimated E from a 100 mm diameter loading plate was LWD found to be 1.5–1.6 times that of a 300 mm diameter loading plate. Vennapusa and White  recommended 300 mm, 200 mm, and 100 mm diameter of loading plates, for the range of E < 125 MPa, E between 125 and 170 MPa, and E > 170 MPa LWD LWD LWD respectively. Plate rigidity The plate rigidity factor depends on the rigidity of loading plate and type of compacted geomaterials as shown in Fig. 2. Mooney and Miller  reported that it might be the tendency of a soil to attain a failure where the stress distribution is uniform. Das  stated that it may imply some consequences of the plate rigidity, but theoretically, a flex - ible plate shows uniform stress distribution for a loaded clayey subgrade and a true rigid plate should not deform under a load. Various thickness of plates (refer Table 3) and their materials, which cause variations in their rigidity. Plate rigidity factors (f ) under the loading plate vary with the stiffness of the plate and compacted geomaterials. Boro - wicka  proposed an analytical solution to evaluate the relative rigidity of the plate (Eq. 4). D uddu and Chennarapu International Journal of Geo-Engineering (2022) 13:6 Page 7 of 13 RigidLoading Plate Inverse Parabolic shape parabolicshape Cohesionlesssand Clay (Elastic material) f = 2.67 f = 0.157 r r Flexible Loading Plate Inverse Parabolic shape parabolicshape Cohesionlesssand Clay (Elastic material) f =2 f = 2.67 Rigidand Flexible LoadingPlate Uniformshape ForMixed material properties f =0.157 to 2 Fig. 2 Schematic view of Plate Rigidity (shape) factors (f ) [12–14] 2 3 E 1 − υ t p p K = (4) 6E 1 − υ s s where; K = Relative rigidity of the loading plate, E and E = Modulus of elasticity of the p s loading plate and compacted geomaterial respectively (MPa), υ and υ = Poisson’s ratio p s of the loading plate and compacted geomaterial respectively, t = Thickness of the load - ing plate (m) and r = Radius of the loading plate (m). For K = 0, the contact stress distribution under the loading plate is uniform and it is considered as a flexible plate, K > 0, the contact stress distribution at the edges increases to infinity and varies at the center of loading plate, and K = ∞, the contact stress at the center of the loading plate is half of the applied stress and it is considered as a perfectly rigid plate. Plate contact stress The contact stress between the loading plate and the compacted geomaterials is assumed to be uniform or that of a parabolic and inverse parabolic for a rigid plate on an elastic half-space (as shown in Fig. 2). The applicability of linear elastic half-space theory to the LWD device, as well as the nature of the contact stress between the loading plate and the compacted geomaterials, must be assessed. The impact force and diameter of the load - ing plate are designed to deliver a peak contact stress in the range of 100–200 kPa, simu- lating the approximate stress pulse on a typical sub-grade or base layer caused by traffic loading on top of a finished pavement [9, 15, 17]; Nazzal et al. . Most of the studies indicated that the measured deformation modulus increases with higher applied contact stress and it depends on the type of compacted geomaterials. For Duddu and Chennarapu International Journal of Geo-Engineering (2022) 13:6 Page 8 of 13 dense and compacted granular materials, E increases with higher applied contact LWD stress and for the materials with cementitious properties and soft subgrade soils are not influenced by change in the contact stress stated by Vennapusa and White . Flem - ing et al.  found that the measured E with a 300 mm diameter loading plate was LWD increased by 1.15 times by increasing the plate contact stress from 35 to 120 kPa. Similar studies on very stiff crushed aggregate and stabilized aggregate materials shown no sig - nificant difference in the plate contact stress from 140 to 200 kPa . The contact stress for the 100 mm diameter loading plate was 8–9 times that of a 300 mm diameter loading plate . Bilodeau and Dore  conducted an experiment with both 100 mm and 300 mm diameter loading plate on Ultra High Molecular Weight Polyethylene (UHMWP) plastic material (properties similar to granular soils). The higher stresses were recorded with the 100 mm diameter loading plate. However, the contact stress distribution for the 100 mm loading plate shows flattening and/or increas - ing stresses near the plate edge. The assessment of contact stress under the LWD loading plate was found to be affected by the diameter of the loading plate. Hence, the contact area has a significant impact on the E . LWD Loading rate and buffer type The rate of loading can be regulated by changing the spring rigidity of the buffer between the drop weight and the contact loading plate and thus can affect the measured deforma - tion modulus. Lenngren and Lukanen  reported that by using stiffer buffer for the case of asphalt concrete pavements, the load pulse time history was shortened and the resulting E is increased by 10–20%. Lenngren and Lukanen  also indicated that LWD the shape of the load pulse, its peak, and time history affects the magnitude of the meas - ured deformations to some extent. Fleming  reported that a comparatively lower stiffness buffer provides more efficient load transfer and better simulates static plate loading conditions. Deng-Fong Lin et al.  also evaluated the effect of drop heights, concluding there was a very low impact of different drop heights on stiffness buffers. The effect of buffer temperature and loading pulse was evaluated by Adam and Kopf . E was measured on the rigid laboratory floor for a fixed drop weight and height LWD at different temperatures. Data for 10 repetitive loading has been recorded with two buff - ers. The applied impulse load varied approximately 30% with a change in the buffer tem - perature from 0 to 30 °C because the rubber buffers are slightly softened when heated due to repetitive loading because of the impact of load on the loading plate is independ- ent of the surrounding and equipment temperature. However, it remains constant for a steel-spring buffer. Hence, the researchers recommend to using the steel spring buffers (Larsen BW et al. 2008) . Location and type of deformation transducer The various LWD manufacturers provide various transducers and their built-in position. For instance, the spring-loaded geophone is used in direct contact with the compacted geomaterial through a hole in the center of the loading plate to measure the velocity of the compacted geomaterial in Keros, Dynatest, Prima, and TFT devices as shown in Fig. 3a. Whereas, the Zorn device has an accelerometer built into the loading plate (Ven- napusa and White 2009)  from which the readings are twice integrated to calculate D uddu and Chennarapu International Journal of Geo-Engineering (2022) 13:6 Page 9 of 13 Drop weight Drop weight StifferBuffer StifferBuffer Load Cell Geophone Velocity Transducer LoadingPlate Accelerometer Compacted material CompactedMaterial (a) (b) Fig. 3 Schematic sketch of the location and type of transducer: a Geophone measures velocity and is located on the compacted material, b Accelerometer measures vibrations and is located in the plate Table 4 Correlations between LWD and other devices for various compacted geomaterials Tested material Empirical/regression correlations R References Sandy soil CBR = 0.0009 E − 0.064 E + 6.904 0.807 Dwivedi and Suman  (us) LWD LWD CBR = 0.0001 E − 0.0015 E + 1.184 0.805 (s) LWD LWD –5 2 γ = 1 × 10 E + 0.002 E + 1.098 0.77 d LWD LWD Lime stabilized subgrade soil UCS = 4.9 E 0.99 Bisht et al.  LWD CBR = 0.15 E 0.93 LWD Lateritic subgrade CBR = − 2.754 + 0.2867E 0.90 Rao et. al  LWD a a Soil classification E = 0.91 E − 1.81 0.84 Alshibli et al.  V1 LWD-P3 0.006ELWD−P3 GC, GC, GW, GP, SP, CL-ML, CL E = 25.25 e 0.90 V2 Cohesive soils E = 0.833 × E – Adam and Kopf  V1 LWD-Z3 Non-cohesive soils E = 150 ln [180/(180 − E )] or – V1 LWD-Z3 E = 1.25 × E − 12.5 (E ranging V1 LWD-Z3 LWD-Z3 between 10 and 90 MPa) Crushed limestone CBR = − 14 + 0.66 E 0.83 Nazzal  LWD Sandy soils E = (600 − 300)/(300 − E ) – Livneh and Goldberg  V2 LWD-Z3 CBR unsoaked California bearing ratio, CBR soaked California bearing ratio, E deformation modulus measured by a (us) (s) LWD lightweight deflectometer (LWD) device, γ dry density of the compacted material, UCS unconfined compressive strength Materials classified as per the Unified Soil Classification System (USCS); Ev = Static modulus of layer 1; Ev = Static 1 2 modulus of layer 2; Eand E = Modulus of deformation measured by Prima 100 and Zorn LWD device with 300 mm LWD‑P3 LWD‑Z3 diameter plate deformation of the loading plate as shown in Fig. 3b. These differences seem to contrib - ute to differences in the evaluation of loading plate deformation. The contact area of the geophone is very disturbed due to the narrow foot of the geophone, and has a relatively stiff spring buffer inside the housing to maintain contact between the geophone and the compacted geomaterials, which results in disturbance (Fleming et al. 2007) . This disturbance is common on softer subgrades and some granular compacted geomaterials. However, it is not clear about the quantifying of recorded permanent deformation dur- ing the impact and effect of disturbance on E . The contact area of the accelerometer LWD loading plate has not reported any such disturbances under it, as it is built into the load- ing plate. Duddu and Chennarapu International Journal of Geo-Engineering (2022) 13:6 Page 10 of 13 Correlations and ranges of deformation modulus (E ) LWD Since LWD tests are easy and rapid to conduct, the testing period can be significantly shortened . Hence, researchers proposed the correlations (refer Table 4) between measured E and other parameters like density, unconfined compressive strength, LWD California bearing ratio, etc. The deformation of modulus range varies based on the type of LWD device used and type of material. Based on available data, the typical deforma- tion modulus reported for various types of subgrades, subbase, base layers, granular lay- ers, and backfilling materials are listed in Table 5. Application of lightweight deflectometer The LWD device is a new evolution through the use of its best practice and simple oper - ating principle, moreover internationally recognized and widely accepted for infrastruc- tural applications in recent years after being used over 34 years in European countries (i.e., Germany, United Kingdom, United States, Australia and New Zealand on a per- formance design basis). The several advantages of the methods are likely to benefit the Table 5 Typical range of deformation modulus (E ) for various compacted geomaterials LWD Type of material E (MPa) References LWD High binder Reclaimed asphalt pavement (100%) 203 Akmaz et al.  Virgin aggregate (100%) 129 Aggregate base layer post-construction with and without 79 Jason et al.  geogrid and geotextile Well and gap graded gravel sand 35–60 Choi et al.  Coarse-grained sand 69–132 Dwivedi and Suman  Cohesive soil 5 Barounis  Very soft clayey silt 8–14 Loose to medium dense silt 17–27 Dense to very dense compacted gravel (moist–dry) 40–64 Lime stabilized subgrade 94 Bisht et al.  Compacted Base 45–60 Umashankar et al.  Surface layers 105–120 Cement modified crushed stone 63.5 Matthew et al.  Lime modified crushed stone 68.5 Non-modified crushed stone 37 Bituminous surface layer 170–190 Prakash and Rakesh  Calcareous Sand (D = 20–80%) 8–35 Elhakim et al.  Siliceous Sand (D = 20–80%) 12–43 Soft clay subgrade 48 Silty sand 13.5–63.5 Kim et al.  31–105 Asphalt 110–140 Poorly compacted sub base 5–81 Granular sub base 100 Natural subgrade 67–78 Deng-Fong Lin et al.  Clayey soil (Optimal), dry and wet 31, 50 and 28.5 Khalid et al.  Crushed limestone 74–131 Recycled Asphalt Pavement (RAP) 138 Granular sub base 50 D uddu and Chennarapu International Journal of Geo-Engineering (2022) 13:6 Page 11 of 13 sectors, such as monitoring of compaction activities of earthworks, pavements, run- ways, embankments, retaining walls, mechanically stabilized earth walls (MSE), land- fills, compressibility of waste or contaminated land, marine works, treated and untreated soil, canal construction. In addition, a new testing procedure has been implemented to obtain direct measurements of resilient modulus (M ) of a compacted geomateri- als using a simple technique and it was designed for both laboratory and in-situ testing . Recent studies have been carried out based on the forward and back-calculation solutions, which are formulated as an inverse problem to match the predicted defor- mations to the observed deformations by using most existing techniques such as static back-calculations use regression equations that are fitted to a database of deformations by using artificial neural network system (ANNS)  and by employing gradient search or genetic algorithm iterative methods to minimize an objective function of any set of independent variables (i.e., thicknesses and layer moduli) . The instant results of the compacted geomaterials obtained from LWD makes it an effective device and an ideal replacement, saving time and minimizing the cost. The deformation modulus value depends on various factors such as the diameter of the load- ing plate, drop height, contact stress, and flexural rigidity. Hence, researchers recom - mend that the range of deformation modulus values need to be exercised for a selected geomaterials by constructing a test pad before proceeding to the actual construction. Conclusions The lightweight deflectometer (LWD) device is an internationally recognized and widely used technique in infrastructural applications. The long-term performance of any pro - ject depends on the characteristics of the compacted geomaterials. This study provides a state-of-the-art resource for contractors and engineers by focusing on evaluation of deformation modulus by using various LWD devices and discussed the influence of vari - ous factors on deformation modulus. Several correlations between deformation modu- lus and other engineering properties of geomaterials like dry density, UCS, and CBR. Range of deformation modulus values were presented for various geomaterials. Infield, it is necessary to construct a test pad for evaluating the range of deformation modulus values for the corresponding geomaterials. It is concluded that the lightweight deflec - tometer (LWD) is a valuable and very effective device for monitoring the quality of con - struction as it is versatile, portable, can reduce duration, running cost of major projects, and it is suitable for all construction geomaterials. The LWD has to be deploy in India and other developing countries by the consultants, geomaterial specifiers, contractors, and clients to play a major role in QC/QA in ensuring the safe and solid system of trans- portation and long-term pavement performance along major road network corridors. Abbreviations QC: Quality control; LW: Lightweight deflectometer; E : Deformation modulus; MoRTH: Ministry of Road Transport & LWD Highways; SCT: Sand cone test; CCT : Core cutter test; RBT: Rubber balloon test; NDT: Non-destructive tests; MDI: Moisture density indicator; EDG: Electrical density gauge; NDG: Nuclear density gauge; SDG: Soil density gauge; BCD: Briaud compaction device; CH: Clegg hammer; DCP: Dynamic cone penetrometer; SSGG: Soil stiffness geo-gauge; FHRI: Federal Highway Research Institute; HMP: Headquarters of Magdeburger Prufgeratebau; FWD: Falling weight deflectometer; CIV: Clegg impact value; DPI: Dynamic cone penetration index; CBR: California bearing ratio; M : Resilient modulus; ASTM: American Society of Test Method; UHMWP: Ultra high molecular weight polyethylene; GC: Clayey gravel; GW: Well graded gravel; GP: Poorly graded gravel; SP: Poorly graded sand; CL-ML: Clayey silt of low plasticity; CL: Lean clay; RAP: Recycled asphalt pavement; ANNS: Artificial neural network system. Duddu and Chennarapu International Journal of Geo-Engineering (2022) 13:6 Page 12 of 13 List of symbols γ : Dry density of the compacted geomaterial (kN/m ); W: Water content (%); r: Radius of loading plate (mm); υ and υ : d s Poisson’s ratio of the compacted geomaterial; f : Plate rigidity factor; w: Deformation of the loading plate measured at its center (mm); q: Maximum contact pressure (MPa); a: Area of loading plate (mm ); F: Applied force (N); m: Mass of falling weight (kg); g: Acceleration due to gravity, 9.81 (m/s ); h: Drop height (m); c: Material stiffness constant (N/m); K: Relative rigidity of the loading plate; E : Modulus of elasticity of the loading plate (MPa); E : Modulus of elasticity of the p s compacted geomaterial (MPa); υ : Poisson’s ratio of the loading plate; t : Thickness of the loading plate (mm); CBR : p p (us) Unsoaked California bearing ratio (%); CBR : Soaked California bearing ratio (%); UCS: Unconfined compressive strength (s) (kN/m ); Ev : Static modulus of layer 1 (MPa); Ev : Static modulus of layer 2 (MPa); E : Modulus of deformation 1 2 LWD-P3 measured by Prima LWD device with a 300 mm diameter plate; E : Modulus of deformation measured by Zorn LWD LWD-Z3 device with a 300 mm diameter plate; D : Relative density (%). Authors’ contributions DSR: acquisition of data, images, drafting of manuscript and provided the revised article content. HC: provided the area of study, acquisition of data, images, drafting of manuscript, provided the revised article content and final approval of the version to be submitted. Both authors read and approved the final manuscript. Funding Not applicable. Availability of data and materials Not applicable. Code availability Not applicable. Declarations Ethics approval and consent to participate Not applicable. Consent for publication We, the undersigned, consent to the publication of identifiable details, which may include photograph(s) and/or details within the text to be published in the Springer’s “International Journal of Geo-Engineering”. Competing interests All authors have no conflict of interest towards this report. Author details Deptartment of Civil Engineering, Ecole Centrale School of Engineering, Mahindra University, Bahadurpally, Jeedimetla, Hyderabad, Telangana 500043, India. Ecole Centrale School of Engineering, Mahindra University, Bahadurpally, Jeed- imetla, Hyderabad, Telangana 500043, India. Received: 28 May 2021 Accepted: 25 October 2021 References 1. Specifications for Road and Bridge Works of Ministry of Road Transport & Highways (MoRTH), (5th Revision) (2013). Indian Roads Congress and Standard, New Delhi 2. Quintus VHL, Minchin CRE, Nazarian S, Maser KR, Prowell BD (2009) NDT technology for quality assurance of HMA pavement construction. NCHRP Report 626, Transportation Research Board, Washington, DC. https:// doi. org/ 10. 17226/ 14272 3. Ebrahimi A, Edil TB (2013) Light-weight deflectometer for mechanistic quality control of base course materials. Proc Inst Civ Eng Geotech Eng 166(5):441–450. https:// doi. org/ 10. 1680/ geng. 11. 00011 4. 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International Journal of Geo-Engineering – Springer Journals
Published: Dec 1, 2022
Keywords: Quality control (QC); Compacted geomaterials; Lightweight deflectometer (LWD); Deformation modulus (ELWD)
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