Proceedings of the Indian Geotechnical Conference 2022 Volume 7

Mechanically Stabilized Earth (MSE) walls are an alternative engineering structure to traditional reinforced-concrete retaining walls with significant and adaptable height at a lower cost. The main objective of this study is to perform a detailed numerical analysis of the MSE wall considering the effect of parameters such as; reinforced soil, the vertical spacing between reinforcements, the tensile strength of reinforcement, surcharge magnitude, and wall height on the external stability of MSE wall under the static and seismic loading conditions. The analysis has been carried out using the Geo5 numerical tool to obtain the Factor of Safety (FS) against external stability checks. Variations of FS against overturning and sliding for wall-facing and reinforced blocks are compared for various parameters considered in this study. Also, Global Safety Factor (GSF) is analyzed using limit equilibrium methods. From the detailed parametric analysis for external stability of the MSE wall, it has been found that the GFS and the FS against overturning and sliding for wall facing are higher for minimum vertical spacing and greater reinforcement tensile strength. The increased surcharge magnitudes and wall heights reduce the FS. Reinforced soil with well-graded gravel has a significant effect on FS than clayey soil and poorly-graded sand.

Cantilever sheet pile walls are the ancient earth retaining systems extensively used in a deep excavation in congested urban areas adjacent to existing structures. In the present investigation, the two-dimensional finite element method has been implemented to study the behavior of sheet piles under a uniform surcharge strip foundation load placed at different positions from the top edge of the wall in dense sand. Sequential excavation of frontfill soil is done in four layers to incorporate the construction effects during wall installation. The present study has found that a foundation of 2 m width has been the critical one based on maximum wall deformation criteria under surcharge loading irrespective of the foundation's position. A parametric study is performed by varying the wall embedded depth and the foundations position above and below the backfill surface to determine the wall deformation, bending moment, and ground settlement behavior. The wall deflection, bending moment, and ground settlement are maximum when the surcharge load is positioned near the top of the wall. As the surcharge distance increases both above and below the backfill surface from the top of the wall, its effect decreases. The present numerical model validation has been done with available literature.

Construction of an underground metro station box is a deep excavation problem. Ground deformations are inevitable in any deep excavation project due to deflection of retaining wall, dewatering and surcharge. Such ground deformations can affect the serviceability of adjoining over ground structures and underground structures or utilities. In cases of severe surface settlement, safety of such adjoining structures may also be at risk. Several researchers have attempted to predict excavation-induced surface settlement using empirical, analytical and numerical methods. In this paper, the applicability of empirical methods of surface settlement predictions due to braced excavation has been studied. Surface settlement has been predicted considering in-situ soil stratification, retaining structure, depth and width of excavations and factor of safety against basal heave. During construction of station box, surface settlement adjoining the zone of excavation is measured using surface settlement monitoring points. The empirical predictions have been compared with field data from one of the station boxes of Kolkata East West Metro project. The predicted surface settlement agreed reasonably well with observed instrumentation data.

This paper presents a case study of design of slope protection works in the third reach of Vadakara-Mahi Canal in Northern Kerala. The canal has a length of 17.61 km, and the construction works in its third reach have been stalled due to the loose nature of soil and collapsing sides. As the alignment of canal in this reach passes through hillocks and elevated terrains, the depth of cutting involved is very high up to a maximum of 24 m. Many residential buildings are situated on both the banks of the canal, and hence the retaining system and construction methodology adopted should not pose any risk to the safety of these structures. Geotechnical investigation is carried out by drilling six boreholes by rotary boring method. In the first tier, an anchored secant pile wall of height 12 m above the canal bed level is designed, and the passive pressure in front of the wall is enhanced by providing geobags filled with locally available soil. The backfill soil in front of the anchor block is stabilized to improve the passive resistance. In the second tier, a gabion faced retaining wall is designed. For the third tier, a stable slope of height 3 m is designed above the gabion wall, and coir geotextile is provided for erosion control. The global stability is checked by carrying out finite element analyses with the software PLAXIS 2D. The distribution of bending moment and shear force in the secant pile obtained from finite element analyses is used for the structural design.

Expanded polystyrene (EPS) geofoams are used widely in civil engineering projects as it has lightweight and low density. The present study is to analyze the lateral pressures in the retaining walls using EPS geofoam as an inclusion in the backfill. Retaining wall with the height of 6 m is designed and modeled using PLAXIS. Geofoam is included as backfill in various orientations such as upper-triangular pattern, lower triangular pattern, and the rectangular pattern. Optimum orientation with regard to low lateral pressures is found. Using PLAXIS 2D software, seismic analysis is performed in the present model. Bhuj earthquake data is used as the input parameter for examining the seismic behavior. The acceleration response at the top, the middle, and the bottom of the wall with respect to time is plotted, and the peak values are compared. From the study, it is observed that the geofoam reduces lateral thrust by about 50% in seismic condition.

Over the past few years, heavy rainfall-induced storm surge has resulted in coastal erosion and consequent beach loss in Kerala. Shankumugham beach road in the Thiruvananthapuram district is one such road that was earlier protected by a gabion wall along the seashore. During the 2019/2020 monsoon period, the gabion walls and half lane of the road got washed away due to rainfall-induced storm surge. Due to heavy rainfall, the tidal height increased by 21% which led to the erosion of beach soil, including the foundation soil of the gabion wall. To reclaim the beach road, remedial measures in the form of a diaphragm wall with rubble mound and soil anchor were designed and constructed. In the present study, a three-dimensional finite element modeling (FEM) of the diaphragm wall and armor layer was performed considering the dynamic effects of wave action. In addition, a comparative study was done between the 2D limit equilibrium method (LEM) analysis result and the 2D and 3D FEM output under static and dynamic loading conditions. The results from the study verify the stability of the structure in the existing condition.

Retaining walls are built to retain earth filled of greater height. They are widely used in the construction of basement below ground level, rail, and road projects where earth filling is required, wing wall, and many more. The cantilever retaining wall with pressure relief shelf in the side of the backfill gives more economical value than the normal cantilever retaining wall. This study aims to analyze and design the cantilever retaining wall with or without pressure relief shelf. The pressure relief shelf is provided at the mid height of the retaining wall. The analysis and design is done in conventional and soft computing method by using ETABS software. From the study it is found that the effect of lateral active earth pressure exerted on the retaining wall with pressure relief shelf is less than the retaining wall without shelf. The factor of safety against sliding and overturning is more in case of retaining wall with pressure relief shelf and also the area of reinforcement required less for the retaining wall with pressure relief shelf, hence it is more economical.

Retaining walls are usually constructed to retain the backfill soil. However, a seismic study of earth pressure in layered soils is complicated and cannot be reliably predicted due to soil-structure interaction influenced by the backfill soil properties and wall rigidity. The complexity lies in understanding the potential failure surface and the soil arching effects due to the interaction of the soil layers. It is observed that the possible failure surface in the backfill soil depends upon the friction angle between the wall and backfill soil. The failure surface tends to be planar for small friction angles, and a curved failure surface is observed for higher friction angles. Also, under pseudo-static conditions with constant seismic coefficients, the stress distribution in soil along the height of the retaining wall presents a non-linear pattern approaching a curvilinear surface behind the retaining wall in the active and passive case. Moreover, the effect of non-homogeneity due to the layered soils leading to the soil arching phenomenon due to the interaction of soil layers on the distribution of earth pressure is also a concern. This paper describes the distribution of earth pressure in layered c-phi soil, considering the effect of the soil arching phenomenon.

Back-to-back mechanically stabilized earth walls are a common type of reinforced wall. These are used as approach embankments for flyovers and bridges. In the current study, in a laminar box, reduced-scale models of BBMSE walls reinforced with geogrid layers were built. A pneumatic-controlled actuator was used to apply the load. LVDTs, strain gauges and earth pressure sensors were used to instrument the model. Modular block deformations and tensile force distribution of geogrid were represented to assess the performance of the BBMSE walls. Overlapping lengths of the reinforcements were varied, and analyses were carried out. Finite element analysis was carried out to validate the model tests. The results of the numerical analyses were in good agreement with the model tests carried out. A prediction study was also carried out using an adaptive neuro-fuzzy inference system (ANFIS), which is an AI predictive model. The coefficient of determination (R2) and root-mean-square error were determined to evaluate the model.

Earth retaining structures can endure lateral stresses from the held soil as well as additional pressure from neighboring structures foundation, moving vehicles, or any other dynamic movement. While designing retaining walls, the amount and distribution of soil earth pressures are critical. The economy of retaining wall structure is depends on amount of earth pressure developed. Many techniques have been developed in the past to reduce soil lateral earth pressure on wall in order to create a cost-effective design. Provision of pressure relief shelves, use of light weight backfill, and inclusion of compressible geofoam, etc., are a few of approaches used. One of the least explores solution for reducing lateral earth pressure on retaining walls is Introjected backfill retaining wall. Introjected backfill wall consist of pressure relief shelves projected toward backfill side. Static load, i.e., pressure load is applied on backfill soil for numerical simulation. The objective of the present study is to find out how effective relief shelves are at reducing retaining wall deflection and settlement of the backfill under various static loading conditions. A 14 m high retaining wall with and without relief shelves by varying width is analyzed using finite element code ABAQUS2020.

Diaphragm walls are commonly used for supporting deep excavation when there are restricted setback conditions. The behavior of wall is influenced by variation of ground water table, surcharges, type and stiffness of supports, and encountered soil types. In this paper, diaphragm wall with two level of anchors supporting a 12.5 m deep basement excavation in mixed soil conditions has been discussed. There is considerable variation in the level of weathered rock within the project site, i.e., between 15 and 21 m. Panels of varying depth are identified based on the soil/rock conditions at wall toe. The performance of wall for different soil/rock conditions at wall toe has been analyzed by subgrade reaction approach. Design assumptions and results of the subgrade reaction analysis is validated by examining “no rock condition at wall toe” using Finite Element Approach. This paper compares theoretical deflections calculated with subgrade reaction approach with recorded wall deflections and discussed about the performance of retention system for various toe termination levels.

The present study explores the application of locally available compressible inclusions in reducing the lateral earth pressure acting on the rigid cantilever retaining walls retaining dry and cohesionless backfill. A small-scale physical model tests on an 80 cm high retaining wall were performed with the presence and absence of inclusions. The backfill at relative densities of 65, 50, 40, and 35% were modeled in the study. The effects of different types of inclusions and relative density of the backfill soil were analyzed. The obtained lateral earth pressure from the study was compared with that obtained using Rankine’s theory. It was observed that when the surcharge load and the relative density of the backfill increase, the lateral earth pressure increases and decreases, respectively. The results showed that the isolation efficiency of coir fiber was greater than bed waste when used as inclusion.

The abutment-backfill system plays an important role in transferring laterally generated forces from the bridge deck to the foundations on either end of the bridge. The soil used as the backfill material dictates the behaviour of the abutment-backfill system by mobilizing the forces in the form of stress. In a seat-type abutment, the in-plane lateral resistance is provided both by backfill and underneath piles, but the out-of-plane movement is mainly restricted by piles. It is necessary to study the behaviour of the abutment-backfill system under lateral loading. In the present study, a continuum 2D abutment-backfill-pile model is developed in OpenSees conforming to the site conditions of the Rohtak Railway Bridge project. Initially, a monotonic and cyclic pushover analysis is carried out to estimate the monotonic and cyclic capacity in terms of load–displacement curves. Two types of lateral loading conditions are chosen such as monotonic loading and sinusoidal loading. The global level behaviour at the critical positions is estimated to get an insight into the response characteristics of the system.

The finite element (FE) software PLAXIS 2D is used in this study to perform a numerical analysis for the prediction of deformation in the surface layer of geogrid-reinforced flexible pavements for various California bearing ratios (CBR) of subgrade and traffic volume. A linear elastic model was used to simulate the behaviour of base, sub-base, and subgrade soil, whereas geogrid was modelled as a linear elastic geogrid element. The accuracy of the FE analysis was verified by comparison of the outcomes of numerical studies to the findings of the experimental study reported by Correia, 2014. Using the validated FE model, this work has been extended to include geogrid into the base course of flexible pavement. A significant improvement in base layer modulus value was observed for geogrid-reinforced pavement when compared to an unreinforced case. Furthermore, the modulus improvement factor (MIF) for geogrid has been calculated based on the improved modulus value of the reinforced base layer. A comparison between two different types of geogrids, i.e. stiffness of 400 and 800 kN/m, is also analysed on the basis of MIF value.

The construction of embankments on soft soil poses severe challenges to their stability due to the characteristics of the soft soil. Therefore, to overcome the issues of excessive settlement and stability, the soft soil may be improved by including an encased stone column (ESC). Construction features including the stiffness of the encasement material, column length, and encasement length have a significant impact on how an embankment resting on soft soil behaves when modified with ESC. The impact of these construction characteristics on the behaviour of the embankment was therefore examined numerically in the current study using PLAXIS 3D. The soft soil was represented by the soft soil (SS) model, and the stone column, embankment, and sand platform were represented by the Mohr–Coulomb (MC) model. The study results confirm that the settlement decreases with increased encasement stiffness and ESC length. In addition, load transfer mechanism, development of the plastic points, and stress concentration ratio are also significantly dependent on the mentioned parameters.

This paper presents a numerical study of the dynamic lateral behavior of geogrid-strengthened pile foundation systems embedded in layered soil medium subjected to rotating machine-induced vibration. Lateral dynamic responses of the single and 2 × 2 group pile foundation systems are studied without and with geogrid reinforcement using finite element software PLAXIS 3D for different intensities of dynamic force (0.01,0.02 and 0.03 kg-m). For geogrid-reinforced pile foundations, the geogrid is placed at a depth of L/8 (L = length of the pile = 0.6 m) from the top surface of the soil. The Mohr–Coulomb soil model is used to simulate the elastoplastic behavior of soil. The model is validated using the existing results presented in the literature. Results of the numerical analysis are presented in terms of frequency versus lateral displacement amplitude of the pile foundation. From the results, it is found that the inclusion of geogrid in the pile foundation system has improved the performance of both the single and group pile foundation system by reducing the amplitude of vibration. This is because of the increase in the stiffness of the foundation system due to the interlocking effect between the soil-pile geogrid systems.

Increased recent application of geo-synthetic-reinforced soil (GRS) walls as bridge abutments to support bridge beams over shallow foundations is pervasive in place of deep foundations. Understanding the behavior of footing resting on the backfill of the GRS wall is necessary and finding out the bearing capacity of the footing is essential. Many researchers have calculated the bearing capacity of the footing resting on GRS walls by using numerical analysis through various softwares. In the present study, numerical analysis is performed to estimate the effects of various factors, namely embedment depth of footing, angle of internal friction, offset distance of footing, width of footing, and length of reinforcement on bearing capacity. Consequently, an artificial neural network (ANN) is applied to predict the bearing capacity of the footing. For this, 190 data points collected from previous research articles and others processed in PLAXIS 2D software are used in the present analysis. A model equation for the determination of the ultimate bearing capacity of the footing resting on the GRS wall has been developed from the best-fit ANN model. Finally, sensitivity analysis was performed to determine the order of importance of input parameters on the output parameter.

Geotextile tubes are used worldwide for coastal protection against erosion caused by the action of waves and tides. Very few studies are available on the stability of stacked geotextile tubes subjected to scouring. In this paper, finite-element-based numerical analyses were carried out using PLAXIS 2D to study the stability of stacked geotextile tubes subjected to scouring under various foundation conditions. The different cases of ground modifications considered for stacking the geotextile tubes were: (i) flat ground base foundation; (ii) gravel bedding foundation; (iii) excavated foundation; and (iv) excavated foundation with gravel bedding. Considering rubber's excellent energy absorption capacity and the need to replace conventional materials with sustainable alternatives, analyses were conducted to study the potential utilization of waste rubber tire crumbs as infill material. Analyses were carried out with stacked geotextile tubes filled with pure sand and tubes filled with sand and waste rubber tire crumbs of various proportions. The factor of safety, surface settlement, and horizontal displacement at the embankment toe under different water heights were also studied.

Geogrid has been used for the last few decades mainly as a reinforcing material. The application of geogrid in railway embankment formation to lessen the settlement and thereby stress is well addressed by researchers. This literature explores the application of geogrid to arrest the possible shear failure at the rock-soil interface in deep rock cuts for the formation of high railway embankments. The geogrid is fixed to the rock-cut face using anchors and plates with adequate overlap. This provision of geogrids will avoid the requirement of berm formations for the interface stability and this in turn evades the toe cutting of rock mass which may affect global stability. An extensive parametric study is performed by numerical modeling of railway embankments at deep-cut rocks using the finite element tool, PLAXIS 2D. The strength and other parameters of geogrid required for this application are decided by numerical studies and are recommended for field implementation.

Stone columns are usually preferred to enhance the engineering behaviour of soft grounds especially in the case of flexible loaded structures such as embankments. When the clays are very soft with undrained shear strength Su ≤ 15 kPa, a lack in performance of stone columns is reported by researchers. In order to enhance the performance of stone columns, a geosynthetic encasement is provided in the form of vertical encapsulation. Alternatively, they can also be reinforced with horizontal disc-type reinforcements. In the present study, numerical analysis using PLAXIS 2D was conducted to study and compare the performance of an embankment with ordinary and two types of reinforced stone columns. The comparison is made in terms of consolidation settlements, pore pressure dissipation and stress sharing between the stone column and surrounding soil and bulging of stone columns. The influence of parameters, namely friction angle of the stone column material, stiffness of geosynthetic on the consolidation settlements and bulging behaviour are also discussed in brief.

The Assam state in the north-eastern India annually bears the brunt of floods. Displacement of people on the banks of rivers due to erosion is another major issue. The meandering characteristic of Brahmaputra River is so dynamic that Brahmaputra-dyke (B-dyke) from Sissikalghar to Tekeliphuta takes the shape of a bow for nearly 5 km. To protect this area, geotextile tube and geotextile mattress were deployed for the first time in the history of India in the year 2010. This 5 km embankment became a part of the B-dyke which is 27.15 km long. Now, to further provide protection to B-dyke at vulnerable reaches from Lotasur to Tekeliphuta from the erosion of river, geosynthetics materials were used to protect existing embankment to prevent floods and erosion in Dhakuakhana, District Lakhimpur. Such applications are being rapidly deployed to achieve maximum benefit to the community, typically through the use of on-site materials, innovative Geosynthetics materials and construction techniques, where construction is to be completed in a limited time during the flood. The scheme benefits approximately 5 lakh thickly populated villages and protects 10,117 hectares of cultivated and homestead land. The paper briefly presents the problem and protection works carried out along the vulnerable reaches.

Rockwool is an inorganic fibrous furnace product drawn from molten rock and waste slag in the form of interlaced fibers. Owing to its outstanding thermal insulation, durability, non-toxicity, and incombustibility properties, it has found widespread applications in various engineering fields. However, the potential application of this material in the field of ground improvement remains untouched. This study presents an in-depth characterization and review of the potential use of rockwool as a substitute for conventional geosynthetic materials in the field of ground stabilization. The comparison of the mechanical properties of rockwool with commercially available geosynthetics leads to the conclusion that rockwool has mechanical properties lying in the range of natural geosynthetics and can be successfully used as its replacement. To ascertain this, unit cell model tests have been conducted simulating the micropiling ground improvement technique wherein rockwool is provided as an interface between the pile and the expansive clayey soil. These test results have then been validated using the 3D finite element method simulating the model in MIDAS GTS NX, 2021. The laboratory model tests and the finite element simulation results showed that rockwool along with micropiles can be effective in stabilizing weak soil. The micropile with rockwool interface is then simulated as a ground stabilization solution in the subgrade of a 3D railway track model prepared in MIDAS GTS NX, 2021 in order to highlight its benefits.

Geocells are three-dimensional honeycomb shaped geosynthetic material used for ground improvement. It is mainly used for strengthening foundation beds, flexible pavements and for erosion control. In the case of steep and high slopes, it is necessary to provide reinforcements to ensure the stability of structures. In places where foundation is made up of soft soil, foundation reinforcement becomes necessary. Geocells are usually provided in the form of basal reinforcement. Geocells can provide confinement and tensile strength which can help in increasing the factor of safety of slopes. Present study indicates the efficacy of geocell in the stabilization of a lateritic steep slope resting on a clay foundation. Numerical modeling was conducted using a commercially available software PLAXIS 3D. An attempt of modeling of the curvilinear geometry of geocells was done and validated. Slope stabilization using geocell in the form of slope reinforcement and also as a foundation reinforcement was presented in this study. The slope was found to be stable when geocell was provided both as foundation reinforcement as well as along the slope (GCFS) owing to the site conditions, slope geometry, and soil properties.

It is a well-known fact that nowadays finding a construction site with good soil condition is difficult. Kuttanadu region is the largest agricultural area in Kerala, India. The soil in this region is dark brown in color having high compressibility with high organic content. Construction of any type of structures on this soil is still a challenge to civil engineers. Jute is one of the most valuable natural fibers produced extensively in India. The natural fibers are cheap and non-hazardous to mother earth compared to artificial fibers; however in long run, these natural fibers will undergo biodegradation. To reduce the biodegradable nature, it is coated with an alkali, sodium hydroxide. This paper presents the influence of coated and natural jute fibers on the strength properties of Kuttanadu soil. The percentage of fiber by dry weight of soil was taken as 2%, 4%, 6%, and 8%. The effect of length of fiber on the strength properties is studied by using 20 mm and 40 mm length jute fibers. The effect of diameter is studied with jute fibers having 3mm and 5mm diameters. The fibers were soaked in the alkali solution for 24 h and then dried at room temperature for seven days. Coating is done at different percentages of NaOH solution varying from 1 to 30%. Based on the analysis of results, it is concluded that the Kuttanadu soil has been stabilized effectively with the addition of jute fibers, and the durability of the jute fibers is enhanced by the coating of NaOH solution.

This study investigates the effect of three types of bitumen emulsion coating, i.e. dipping, painting, and spraying techniques, on woven sisal geotextiles’ physical and mechanical properties. The physical properties include mass per unit area, while the mechanical properties involve tensile strength and elongation. The results revealed that dipping has the maximum mass per unit area and extension at break compared to painting and spraying. Furthermore, the painting technique gave better tensile strength than spraying and dipping. The study outcomes are compared with the literature wherever applicable.

Small scale laboratory pullout model tests were performed on sand beds having a relative density (Rd) of 70% in the present study. For the tests, a mild steel test tank of 1000 mm (length) × 1000 mm (width) × 1000 mm (height) and circular-shaped anchor size (D) of 100 mm were used. The embedment depth (L) to diameter (D) ratio (L/D) of the anchor plate during the model tests was maintained constantly at 4. For the anchor uplift capacity improvement, the model tests were performed using polypropylene geotextile (PPGT) as a reinforcement material. Furthermore, a series of laboratory model tests were performed to see the effect of number of reinforcements on anchor uplift capacity using single and double number of reinforcements having a size of each 2D and maintained 0.1D and 0.5D vertical spacing (h) for the case of double number of reinforcements. For all the model tests, the first reinforcement was placed directly above the anchor plate. The test results showed that the improvement is higher with double reinforcements at lower uplift displacements compared to the single number of reinforcements. However, irrespective of number of reinforcements, the test results revealed that the amount of improvement of the anchor ultimate capacity is same.

The stone columns (or sand columns) have been utilized to enhance bearing capacity and accelerate soft soil consolidation. To increase the bearing capacity of ordinary sand column, the geotextile-encased sand column technique was recently developed. Furthermore, encasing inhibits lateral squeezing of sand into surrounding soft soil, contributes in the easy formation of sand column, preserves sand frictional properties, and the sand column's drainage function. Through field stress experiments, this research analyses the enhancement of load carrying capacity of ordinary and geotextile encased sand columns. Tests were conducted with various encasement stiffness, sand column diameters, and reinforcement lengths. The results of a field load test showed that the GESCs had a greater load carrying capacity than OSCs. The increase in load carrying capacity is influenced by the encasement length, encasement stiffness, and diameter of the sand column. Furthermore, it was revealed that the partial encasement, which extended from the top of the sand column for a length of two to four times its diameter, had a considerable influence on the performance of the sand column.

Coal ash in one of the thermal plant of NTPC is discharged in wet-form into ash pond created by constructing peripheral ash-dyke embankments. The ash-dyke has been originally conceived with maximum four raisings by upstream method. Further raising beyond 4th raising was not technically feasible by conventional upstream method of raising due to inadequate factor of safety in stability analysis. Also raising by downstream method was not feasible due to presence of water bodies adjacent to toe of starter-dyke. Due to above technical/practical constraints in conventional methods of raising, the alternative was necessitated to ensure the dyke raising for sustaining power generation. With various alternatives explored, it is observed that raising with offset method is technically feasible in instant case. Conventionally, the new raising-dyke is generally constructed abutting the existing dykes, however with evolved offset method of raising, the open offset space between two raisings may be severely affected by sub-surface seepage from proposed new raising. Therefore, the toe-drain of the proposed new raising is to be adequately designed to handle seepage water and continuously divert to toe of existing downstream dyke with cross-drainage arrangements. In NTPC, the 5th raising with above offset (15 m offset) method has been successfully designed, constructed and satisfactorily operated for ash disposal. Through this explored offset method of raising beyond ultimate height, the capacity of existing dyke is significantly enhanced with sustained power generation. This paper presents the details of constraints and adopted new method of design and construction by offset method of dyke raising.

Upstream tailings dam expedites the construction process while lowering disposal and operational expenses. However, these dams are susceptible to liquefaction-induced failure under seismic conditions. This study explores the possibility of reducing differential settlement of the upstream tailings dam under liquefaction by densifying strategic portions of the beach area. Finite Element analysis is conducted using UBC3D-PLM constitutive law to model the liquefiable soil. The model is validated with a published centrifuge model of clayey embankment resting on liquefiable sand. The vertical deformation and post-liquefaction factor for unimproved and improved upstream tailings dam are numerically analysed. For an unimproved upstream tailings dam, vertical deformation to the tune of 300 mm was observed after 100 s of the seismic load, while the post-liquefaction stability factor was 1.33. In order to enhance the stability of the upstream tailings dam, the portion of the beach under the raised embankment was densified at a relative density of 70%. The width and depth of densified portions were varied as a function of beach length. This study suggests a method of improving the stability of the upstream tailings dam under seismic conditions while making the construction procedure of these dams easy and cost-effective.

Analysis by numerical modeling software PLAXIS 2D is carried out for the earth dam of Kurha-Vadhodha Islampur sinchan yojana, Maharashtra, India to optimize seepage remedial measures. Depending on the dam cross-sections and foundation stratification, four cases (A, B, C, and D) are analyzed. Results of analyses indicate that for design dam cross-sections, major seepage is occurring through dam foundation with total discharge quantities of 0.7102, 0.7738, 0.2699, and 0.7169 m3/day/m, respectively. As these values are more than the permissible limit, seepage mitigation measures are required to be adopted at site. To determine the most effective remedial measure, analyses are conducted with: (i) rock grouting, (ii) cutoff wall below CoT, and (iii) upstream horizontal blanket in combination with a 6 m deep cutoff wall. Trials are conducted with different depths of cutoff wall and different lengths of horizontal blanket for optimization. For each trial, efficacy is determined by comparing discharge quantity with the permissible limits. Results indicate that seepage discharge quantities with cutoff wall of depth 35 m, 30 m, 5 m and 15 m for cases A, B, C, and D are 0.1936, 0.1892, 0.1602 and 0.1751 m3/day/m, respectively; which are less than the upper permissible limit. Hence, cutoff wall of above depths is recommended as the most effective seepage remedial measure for the earth dam of Kurha-Vadhodha Islampur sinchan yojana.

Flood embankments are usually constructed along river banks using locally available materials to prevent loss of human life, infrastructure, and valuable property that can be caused by catastrophic floods during the monsoon season. Since they are built along the river plains, these structures are vulnerable to many problems, majorly due to seepage, and hence should be repaired or upgraded timely. In this paper, numerical analyses have been performed to investigate the stability of flood embankments when upgradation is done. Two different types of flood embankments have been considered, i.e. homogeneous and zoned, and are analysed in both steady state and complete drawdown conditions. For the case of homogeneous embankment, different types of upgradation processes are considered: widening on both sides, widening on one side, and without widening. For the case of the zoned embankment, the permeability of the core is varied, and stability is assessed. The results demonstrate that the downstream slope is more vulnerable to collapse in steady state conditions, while the upstream slope is most vulnerable in drawdown situations. In addition, the flood embankment widened on both sides is the most stable compared to the other types. Also, incorporation of an impervious core along with toe drain has also shown better results and can be recommended where the location area is confined.

Slope stability is a matter of tremendous concern in construction of earthen dams where the failure of slopes may incur severe loss of life and damage to property and should be designed in such a way that it satisfies both safety and economic consideration. The basic design requirement of earth dam is overtopping, stability analysis and seepage control. Slope stability chart are useful for preliminary analysis before using a computer programme to determine the approximate values of the Factor of Safety (FoS) as it allows some quality control and a check for the subsequent computer-generated solutions (Salmasi F, Pradhan B, Nourani in Prediction of the sliding type and critical factor of safety in homogeneous fnite slopes. Applied Water Science Journal 9:158–169 [1]). Another use of slope stability charts is to back calculate strength values for failed slopes to aid in planning remedial measure. The various design charts available in literature are Taylor stability chart, Spencer Chart, Bishop and Morgenstern Chart, Michalowski Chart etc. The primary objective of the study is to identify the stability of a proposed homogeneous earthen dam composed of low compressibility clay (CL) to be constructed in Eastern Part of India. The study focusses stability of adopted section for End of Construction, Steady State Seepage and Rapid draw down condition using SLIDE 2D (Rocscience) software (Bishop Method) as well as with design charts. In the present study, Taylor Chart for End of construction condition, Bishop and Morgenstern Chart for Steady state seepage condition and Morgenstern Chart for Rapid draw down condition have been used.

To meet the water requirements of the habitants of Gokuldham Vedic village, composite earthen dam is proposed across a stream flowing through the area. Surveying of the catchment area and the dam site was done to arrive at various quantities necessary to plan and design the proposed dam. The main aim of this project is to construct the dam using naturally available materials by excluding man-made materials such as cement and machineries without affecting the local ecology of the region. Soil from different sources within the property was tested for suitability to construct different parts of the dam. These test results are presented in this article. A detailed report including estimated quantities and cost of construction is submitted to the village panchayat for the approval of budget. The construction will begin after its approval. This article briefly describes the entire process of planning, designing, and quantity estimation for the proposed earthen dam.

The construction of embankment dams is most common and popular due to the easy availability of material. The important point during the construction and after completion of an earthen embankment is the control of seepage through the dam body and foundation. Seepage control is necessary to prevent the downstream slope from sloughing, uplift pressures, piping phenomena, and loss of materials from the dam body to the outside of the dam body. The present study has been carried out on the Tamta earthen embankment which is located in Pathalgaon, Chhattisgarh. The existing dam has been selected for a case study because it has been recently approved for renovation work by Chhattisgarh Government due to leakage through Masonry and the RCC barrel. Hence, it is required to ensure the safety of the dam against seepage. A two-dimensional seepage analysis has been carried out using the computer-aided software SEEP/W to determine the seepage quantities. Results are presented for three conditions, i.e., maximum pool level, normal pool level, and minimum pool level.

Seepage through an embankment must be controlled to prevent concealed internal erosion and migration of fine materials. It is extremely important to control the seepage flow and inhibit removal of the soil particles comprising the dam body. Modern design practice incorporates this control into the dam design through the use of internal filters and adequate drainage provisions. The seepage analysis theories proposed by researchers like Casagrande, Schaffernak, Dupuit, and Pavlovsky for homogenous earthen dam resting on impervious base finds their application in estimation of filter dimension. This paper reports the utilization of machine learning in this regard. A large dataset is generated by using Schaffernak’s theory for phreatic surface assessment and by varying the governing parameters in all possible range that affects the filter dimension. The dataset is used for training in suitable algorithms related to Multilayer Perceptron (MLP), Random Forest (RF), Support Vector Regression (SVR), Ridge Regression (RR), and Xtreme Gradient Boosting (XGBoost) algorithms. The results illustrated that XGBoost algorithm could potentially be used to estimate filter dimension and exit discharge. These trained models can be used as a ready reference solution by the practising engineers, which provides them a preliminary idea for designing toe filters.

The river Barak is the second largest river in the state of Assam. It originates from the hills of Manipur and flows through three states namely, Manipur, Mizoram, and Assam. It bifurcates into two parts Surma and Kushiara before entering into Bangladesh and finally discharges its water to the river Meghna. The river Barak is highly meandering and changes its course frequently, thereby destroying the river side villages every year. Three years ago, the abutments of a bridge were constructed on both the banks of the river. During peak monsoon time, the river changed its course, destroyed one village completely, and started flowing along a new route whereby both the abutments were shifted on one side. The present study includes detailed survey of the river at some other eroding location. The total station survey and bathymetric survey were carried out to obtain the cross sections of the river, geotechnical survey included borelog survey for characterizing the soil layers and geophysical survey was intended to obtain the continuous profile of the substrata. Finally, PLAXIS 3D software was used to obtain the probable deformations and factor of safety of the river banks under steady state, slow draw down, and rapid draw down conditions. Important conclusions were drawn at the end of the study.

The balance work at the Teesta VI Hydro Electric Power Project requires construction of the reinforced diaphragm wall along with watertight upstream coffer dam construction towards the right embankment of the existing barrage. The soil profile at the barrage location is mainly made of large sized boulders and river born material deposited over a period. The subsoil consisting of boulders to be drilled to depths of 36 m below ground level for installation of Jet Grouted Columns. Trails columns are installed before start of the main works of diameter 1.4 m, 1.6 and 1.8 m to establish the parameters of the main works. The jet grouted columns are installed to create a watertight barrier on the upstream side beneath the cofferdam for contraction of the diaphragm and protect the barrage from the underground seepages. Symmetric predrilling with air-driven DTH and casing OD of 152 mm and ID 133 mm casing are used for drilling. Dulex Double Water system (W/B) was used for the installation of jet grouting columns. This paper discusses the installation of the trail jet grouting columns and execution of the main works through the boulder soil profile in the lower Himalayan regions.

The Jannah Dam is designed as a massive arch-gravity dam with a height of 162 m above foundation. The dam is built in a steep valley with heterogeneous ground conditions: granular soils, boulders of limestone, basalt and chert, and underlain by rock. The fresh rocks—limestone and dolostone—have compressive strengths up to 60 MPa. Between 2017 and 2021, Bauer Lebanon executed various foundation works on site, including about 9.500 m2 of plastic concrete cut-off walls (CoW), at both cofferdams, extending over a length of 128 m (U/S) and 161 m (D/S), in addition to multiple rows of overlapping diaphragm walls (d-walls), as a bulkhead. This execution concept, proposed by Bauer instead of originally considered jet grouting block, supports the deep excavation to the foundation level of the dam. The arch-shaped d-walls, with a depth of 38 m at deepest excavation axis, totaling to 3.610 m2, were constructed mostly in zones of noticeable permeability, which exacerbated the challenges imposed by the locally encountered artesian conditions. The three parallel walls, each with a wall thickness of 120 cm, are connected by a capping beam. A secant pile wall was used for subsoil improvement in the area of a geological fault. Grout curtains were constructed along the embankment foundation and in the abutments, while consolidation grouting of the rock was executed under the highly stressed parts of the foundation. The drilling depth reached about 94 m. Special rails have been installed on the slopes to allow safe and accurate drilling and grouting works on slopes fulfilling strict quality and safety requirements.