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About this book

This book comprises select proceedings of the annual conference of the Indian Geotechnical Society. The conference brings together research and case histories on various aspects of geotechnical and geoenvironmental engineering. The book presents papers on geotechnical applications and case histories, covering topics such as (i) Characterization of Geomaterials and Physical Modelling; (ii) Foundations and Deep Excavations; (iii) Soil Stabilization and Ground Improvement; (iv) Geoenvironmental Engineering and Waste Material Utilization; (v) Soil Dynamics and Earthquake Geotechnical Engineering; (vi) Earth Retaining Structures, Dams and Embankments; (vii) Slope Stability and Landslides; (viii) Transportation Geotechnics; (ix) Geosynthetics Applications; (x) Computational, Analytical and Numerical Modelling; (xi) Rock Engineering, Tunnelling and Underground Constructions; (xii) Forensic Geotechnical Engineering and Case Studies; and (xiii) Others Topics: Behaviour of Unsaturated Soils, Offshore and Marine Geotechnics, Remote Sensing and GIS, Field Investigations, Instrumentation and Monitoring, Retrofitting of Geotechnical Structures, Reliability in Geotechnical Engineering, Geotechnical Education, Codes and Standards, and other relevant topics. The contents of this book are of interest to researchers and practicing engineers alike.

Table of Contents

Frontmatter

Behaviour of Geosynthetics Clay Liner Under Direct Shear Test

Geosynthetics clay liner system is a key component of the engineered landfill. Both the internal and interface strengths of geosynthetics clay liner are very important for evaluating landfill stability. This paper presents a study on interface shear strength behaviour between geosynthetics clay liner and sand, and geosynthetics clay liner and Powai soil making use of a direct shear test. The experiments were carried out using dry state and submerged state of sand, and optimum moisture content and submerged condition of Powai soil. The interface shear strength of geosynthetics clay liner and sand, and geosynthetics clay liner and Powai soil found to be lower than the corresponding shear strength of sand and Powai soil. The apparent adhesion was increased, and interface friction angle was reduced during submerged condition.

Aditya Kumar Bhoi, Sunil Kumar Ahirwar, Jnanendra Nath Mandal

Effect of Saturation and Cementation on the Stiffness of Gypsiferous Soils

Gypsiferous soils are found in several arid regions of the world and are known to cause structural hazards due to their collapsible nature. The collapsibility of gypsiferous soils is dependent on a number of soil parameters and gypsum content is one of the key factors. Gypsum acts as a weak cementing agent in the soils. In terms of macroscale procedures for site suitability investigations, the non-destructive testing methods, using shear-wave velocity measurements, are valuable to quickly characterize the stiffness properties of the sites and subsurface soil conditions. In this study, free-free resonant column testing was used to study the shear-wave velocity patterns of reconstituted specimens of sand and gypsum under different degrees of saturation. An overall increase in stiffness was observed with decrease in degree of saturation. The rise is stiffness was attributed to a combination of cementation and matric suction processes. Cementation was observed in specimens containing gypsum. For soils with less than 30% gypsum content, matric suction was a dominant factor in increasing the stiffness of the soil and cementation effect was not very strong. For soils with gypsum content of 30% or more, an appreciable amount of cementation was observed and matric suction showed little impact. The peaks in shear-wave velocity caused by matric suction were replaced by a plateauing feature. Using the soil water characteristic curve approach, regression relationships were developed to determine the contributions of matric suction and cementation toward the change in stiffness of the soils. The results from this study can be used to predict the stiffness behavior and gypsum content of gypsiferous soils in the field.

Raghava A. Bhamidipati, Michael E. Kalinski, L. Sebastian Bryson

Experimental Evaluation of Bearing Capacity of Single CFG Pile

Nowadays, geotechnical engineers are facing the problem of soft ground, which results into low bearing capacity and excessive settlement. On contrary, cement fly ash and gravel (CFG) pile is one of the emerging ground improvement techniques, which can be applied to enhance the load carrying capacity of the soft ground. It also reduces the possibility of settlement associated due to soft ground. This paper addresses the practical real-time results of laboratory model of single CFG pile. Moreover, the comparative evaluation between simulation results (i.e., numerical analysis) and laboratory model has been carried out considering variation in parameters such as diameter of the CFG pile, length-to-diameter ratio of CFG pile, and gravel particle size. The results obtained from this analysis clearly prove superiority of CFG pile over soft ground in terms of enhancing load carrying capacity.

N. B. Umravia, C. H. Solanki

Comparison Between Casagrande Method and Cone Penetrometer Method for Determination of Liquid Limit of Soil

The liquid limit is an essential property of soil due to its relationship with other properties and behaviour of soil directly or indirectly. The two methods for determining the liquid limit are widely used, viz. Casagrande method and cone penetrometer method. This paper presents a comparison of the liquid limit of soils determined by performing both experiments. The result demonstrates that the liquid limit value obtained from Casagrande method is a little higher than those obtained from cone penetrometer in high plastic soil. In low plastic soils, cone penetrometer gives the higher values of liquid limit. However, in medium plastic soil, it is difficult to make any conclusion.

Preksha Jain, Jennie Gandhi, Sudhir Trivedi, Rajesh P. Shukla

Predictive Models for Estimating the Coefficient of Permeability for Sands

Particularly, for granular soils, several correlations are available in the literature for predicting the coefficient of permeability of soils as a function of particle size, properties of pore fluid, void ratio, shape of particles, etc. In this paper, a comparative study of some of the existing predictive models is presented to examine how far these are applicable to natural sands. With the above in view, coefficients of permeability of two different types of sands (sub-angular Ganga sand and rounded Ennore sand) were found out with varying void ratios by constant head laboratory test. The laboratory test data is compared with various predictive models available in the literature. This study highlights the fact that there exists no unique relationship that would be the panacea for predicting the coefficient of permeability values for all types of soils. The expressions as given by Kozeny–Carman, Taylor and Chapuis are rational and scientific. These may be used for quick predictions of the coefficient of permeability, but the coefficients and parameters appearing in these equations need to be properly determined specific to the concerned soil.

Indra P. Acharya, Anubhav, Prabir K. Basudhar

Geotechnical Characterization and Mineralogical Evaluation of Soils in Srinagar City, Jammu and Kashmir

Srinagar city in the Kashmir valley of Jammu and Kashmir state has been studied to understand the types of soils present in the city. Disturbed and undisturbed samples were collected from 30 locations at a depth of 1 m in the main city. Index properties and engineering properties were evaluated from the geotechnical laboratory tests. X-ray diffraction technique was used to determine the mineralogical composition. Results indicate that soils at this depth in Srinagar city are predominantly fine grained. The proportion of clay size in the soils ranges from 7% to high values of about 42% in Batpora and Hawal. The soils have been classified as silty or clayey soils having intermediate to high plasticity according to the Indian Standard and Unified Soil Classification Systems. Low swelling potential and low activity were observed during laboratory tests. This behavior is supported by mineralogical analysis which revealed presence of Quartz and Illite minerals in the soils. Absence of high swelling minerals makes the soil less problematic. Shear strength parameters (c and φ) were found to be low to medium except in few areas like Hariparbat, Harwan, Cheshmashahi and a few areas in the central portion of the city. This suggests that bearing capacity of the soils is less and thus needs attention before starting any engineering work.

Falak Zahoor, K. Seshagiri Rao, Mohd Younis Hajam, Irfan Ahmad Kumar, Hilal Ahmad Najar

Determination of Volumetric Shrinkage of Soils by Dish Method

Shrinkage characteristics of soils are very important parameters for consideration in the design of a safe and stable foundation. Volumetric shrinkage test gives a very effective idea about shrinkage behaviour of the soils. Bureau of Indian Standards (BIS) recommended the method of test for soils, for determination of shrinkage factors, as per Indian Standards IS: 2720 (Part 6)—1972 (Reaffirmed 1995). This method is commonly used to determine various shrinkage factors of soils. This laboratory method is very sophisticated, costly and time taking method. Generally, this test is not available easily in the middle class and small towns, and everyone cannot afford the expense of this test. Authors developed an alternative method named “Dish Method” to determine volumetric shrinkage of soils. The study suggests a very simple, quick, effective and economical procedure for the determination of volumetric shrinkage of soils by steel dish, plastic dish and paper dish methods. The proposed method provides a preliminary idea about the shrinkage characteristic of cohesive soil.

Sanjay Kumar Verma, Sagar Shrivastava, Saleem Akhtar, Rajesh Bhargava

Comparison Between the Soil Properties of the Coastal and Interior Regions of Gujarat

Constructions in the coastal region have been a huge challenge in the civil engineering world for long years, and so, a solutions for the same have to be devised. To study this problem, this paper deals with the soil properties of some coastal belt places of Gujarat region and the soil properties of the non-coastal region of Gujarat. Gujarat’s soil type has a wide range of classification, and so, the different properties like the N-value, type of sample, the depth at which the sample are obtained, type of soil in that region, depth of water table, moisture content, field dry density, the Atterberg limits are studied. After studying these properties from the soil reports obtained from various laboratories, a comparison is made between the soil at coastal belt region and non-coastal belt region of Gujarat and the variation is observed in the various properties. Considering, a school building at Hathab, which a coastal belt location, the N-value varies from 10 to 20 blows in a 6 m considered depth. While considering a building at Bhavnagar district, which is away from the coastal area, the N-value varies from 12 to 23 blows in a 6 m, considered depth. While considering the dry density at Hathab, it varies from 1.48 to 1.62 g/cm3, and the dry density at Bhavnagar district varies from 1.47 to 1.49 g/cm3, considering 6 m depth. These differences need to be studied, and it will helpful in designing suitable design solutions. Thus, this paper may contribute in future research studies to improve and strengthen soil properties of the coastal region.

Param Shah, Manas Kumar Bhoi

Effect of Plastic Fines on Geotechnical Behavior of Ennore Sand

The soil is usually found in the combination of various size particles such as clayey silt, sandy silt and silty-sand. The geotechnical properties of soil such as index properties, permeability, compactability, shear strength and volumetric response rely on the gradation of the soil particles. In the present study, Ennore sand is used with varying kaolinite clay contents such as 0%, 5%, 10% and 15%. To determine the shear strength parameters of soil mixture, a series of large direct shear tests were conducted on Ennore sand–kaolinite clay mixtures. The specimens for direct shear tests were prepared at optimum moisture content and maximum dry density. The experimental results showed that shear strength increased with the increase in fines content up to 10%, and after that, it was observed to decrease. The cohesion of soil mixtures were found to be increased with the increase in kaolinite content due to its plastic nature.

Sagarkumar Khunt, Ajanta Sachan

Effect of Relative Density on Elastic Properties of Sand

This investigation presents the variation in modulus of elasticity and modulus of subgrade reaction of dry sand with respect to change in relative density of sand. The sand was collected from Orsang River and Narmada River (Poicha). The effect of the relative density of sands on both elastic properties was carried out at 40%, 60% and 80% relative density. Modulus of subgrade reaction was obtained by performing model plate load test and modulus of elasticity using simple triaxial test. Correlations between modulus of elasticity and modulus of subgrade reaction developed by various investigators were found from the literature review, and it was observed that the pattern of changing of modulus of subgrade reaction with respect to change in the relative density of sand obtained in the present study was nearer to correlation developed by Vesic and Selvadurai. It was also observed that as relative density of sand increased the modulus of elasticity and modulus of subgrade reaction were also increased.

Arpita V. Patel, Nitin H. Joshi

Characterization and Stabilization of Red Mud and Ash—Solid Industrial Waste from Aluminum Industry

Ore processing and metal manufacturing industries generate huge quantity of residual wastes. Emphasis has been laid on the residual products of aluminum industries, e.g., red mud. The industry utilizes bauxite as raw material to extract aluminum out of it. Extraction of aluminum being power intensive, all the aluminum industries have captive power plants which generate huge quantity of ash as waste product in addition to red mud which comes out through the process of alumina (Al2O3) extraction. In the absence of any effective technology that can utilize red mud, industries have to incur heavy expenses in terms of land and space for storing red mud resulting in increased cost of aluminum production. Such a situation calls for an effective, economic and environment-friendly method to combat the challenges of disposal of the waste produced by such industries. One of the most common and feasible ways to utilize red mud in bulk is to utilize the wastes for civil construction, e.g., construction of embankments, roads, etc., utilizing the waste material. This paper aims at characterization of the waste material, i.e., red mud and ash through laboratory experiments. Analyzing the various aspects of their geotechnical parameter attempt has been made to characterize the mix of ash and red mud as well as cement and red mud. Result obtained through laboratory experiments has been discussed.

A. Ghosh, Dalip Kumar, Zamir Ahmaed

A Study on Effect of Mica Content on Engineering Properties of Sands

It is often necessary to understand the interaction of mica mineral with the fine aggregates which is often used for construction purposes. Mica is one of the known deterious minerals which affects the engineering properties of sand and which ultimately affects the concrete. Different research work has already being conducted by different researchers. In the present study, an attempt has been made to study the effect of mica on different engineering properties. Here, the percentage of mica by weight adopted for different test procedures are 2%, 4%, 6% and 8%. Direct shear test, standard Proctor test, CBR test and compressive strength test were conducted by percentage replacement of locally available sand by mica. From the laboratory test results, it established that the presence of mica in fine aggregates causes reduction of compressive strength, and it increases the water demand. The dry density value, shear strength and the CBR value also reduce with the presence of mica content.

Rajesh Deb, Indira Baruah Gogoi

Study of Thermal Conductivity of Soils for Varying Density and Water Content Profiles

In Analytical Theory of Heat, 1822 Joseph Fourier stated, “The problem of terrestrial temperatures presents one of the most beautiful applications of the theory of heat.” The experimental schedule is planned so as to study a wide variety of artificially mixed soil using naturally available single component soils, i.e., sand, silt, and single mineral clay (kaolinite), to remove heterogeneity due to variation of various minerals in naturally occurring soils for the thermal conductivity as measured in laboratory setup, on the basis of physical properties of the soil. The objectives of this investigation of the thermal conductivity of soils are to employ the thermal probe method to obtain reliable thermal conductivity data for different local natural soils. For evaluating the radial flow of the heat, the soil is compacted in porcelain pipes. It has thermocouple controlled vertical heater rod placed at the center as source and 20 thermocouples placed radially in four directions perpendicular in plan for temperature profile readings. The second setup fabricated in house was aimed at studying the flow of thermal energy in longitudinal direction as well as with depth for which a rectangular steel tank was fabricated. The heat source was placed at one end of the tank, whereas the thermocouples were placed all along the length and a second row placed at different depths along the length. The influence of soil properties such as water content, dry density, and porosity on thermal conductivity is also observed.

Pooja Bhojani, L. S. Thakur, D. L. Shah

Electrical Resistivity Tomography in Geotechnical Engineering Applications

Characterization of subsurface soil is essential for foundation design of important civil engineering structures. In conventional geotechnical investigation, the soil profiling and their characterization are done by collecting samples from the field either through open pit sampling or through boring and then performing laboratory test for their classification and determination of strength and compressibility characteristics. In-situ methods like standard penetration test (SPT), cone penetration test, e.g., static (SCPT) and dynamic (DCPT), pressure meter test (PMT), and dilatometer test (DMT) are also available. But these methods are time consuming and costly. If vast tracts are to be investigated for preliminary exploration, then geophysical methods can aid to collect information about the subsoil conditions. Geophysical methods allow to measure physical properties like electrical resistivity, seismic wave velocity, electrical permittivity, magnetic intensity, etc. These observations can be used for surveying large tracts or ancient structures composed of dissimilar materials. Apart from these, some problems that vex the civil engineers is significant increase in the permeability of desiccated soils due to cracks in these soils due to shrinkage. Such a situation may lead to the progressive failure in flood embankments. Geophysical methods have great potential to aid archeological investigation in identifying archeological features in unexcavated areas. Electrical resistivity tomography (ERT) is very commonly applied in such studies because of its adaptability in identifying walls, cavities, etc., at different depths. The paper pertains to the potential of application of ERT in geotechnical and archeological investigation providing an overview and its use in subsoil profiling and detection of foundation details of old structures. The power of the method in identifying the hidden features of buried objects and subsurface profiling has been demonstrated with examples.

Deepak Sagar, S. B. Dwivedi, Parbir K. Basudhar

Analysis of Physical Modeling of Cast-In-Situ Concrete Piled Raft

Nowadays, there is competition for constructing high rise buildings, and the reason may be due to decreasing availability of land due rapid industrialization and urbanization. This has increased heavy load, complicated stress conditions, and having limitation of bearing capacity of soil. This results in settlement of high rise buildings. This leads to use of piled raft foundation. But the load-bearing capacity of piles is not considered, they are used as settlement reducers only, and load is carried by raft only. In another design method, axial capacity of the piles to carry the structural load and bearing capacity of raft is neglected. In both the design approach, piled raft foundation becomes uneconomical. Now research is going on for considering the load-bearing capacity of both pile and raft and developing detail analysis. In a pile raft foundation, pile-soil-raft interaction is complicated. Although several numerical studies have been carried out to analyze the behaviors of piled raft foundations, very few experimental studies are reported in the literature. The available laboratory studies mainly focus on piles made with steel or aluminum. The present study aims to study the behaviors of piled raft foundation, in the laboratory using physical model. The physical model is made up of cast-in-place reinforced concrete piles, and reinforced concrete raft are used for the tests. The test is conducted on single pile, pile group, un-piled raft, free-standing pile group, and piled raft foundation. We examine the effects of numbers of piles, the interaction between different components of foundation, and load-sharing ratio of pile and raft. The results indicate that the ultimate bearing capacity of the pile raft foundation is considerably higher than that of free-standing pile group with same number of piles.

J. M. Raut, S. R. Khadeshwar, S. P. Bajad

Assessment of 3D Consolidation Settlement of Soil by Considering the Effect of Surcharge Pressure

The aim of the study is to assess 3D consolidation settlement of soil by considering the effect of surcharge pressure on surrounding soil. In this study, a 3D consolidation apparatus is developed and performed a series of 3D consolidation test under different surcharge pressures. Silty-clay soil and silty-sand with clay soil are used in this study. Consolidation tests are performed under different surcharge pressures like 0.0, 10.0, 15.0, and 20.0 kN/m2. From this study, it is observed that with the increase of surcharge pressure, the compression indices and coefficient of consolidation values decrease for both the soils. The surcharge pressures have a significant effect on consolidation characteristics. With the increase of surcharge pressure on the surrounding soil, the void ratio of surrounding soil reduces, and it becomes denser, and as a result, the lateral strain of soil particles under consolidation as well as lateral extractions of pore water reduces, and corresponding compression index and the rate of consolidation also reduce. During the consolidation test as this apparatus allows vertical and lateral strain with vertical and lateral pore water dissipation under different surcharge pressures, it can be simulated to the in-situ field consolidation settlement.

Arpan Laskar, Sujit Kumar Pal

Compaction Characteristics of Red Earth and Quarry Dust Combinations

Quarry dust is a waste material obtained during the quarrying process. It exhibits high shear strength and good permeability. An efficient method to dispose it off is by using it in combination with red earth to strengthen the soil. This paper presents effects of addition of quarry dust on properties of red earth and the relationship between water content and dry density of quarry dust–red earth mixes. Preliminary studies concluded that the optimum proportion of quarry dust–red earth mixes was found as 40% and 60%, respectively. The optimum values of the mixes are defined with respect to the dry density of quarry dust alone. It is observed that there was an increase of 11.61% in the dry density when 40% of the red earth is replaced with quarry dust. The optimum value of quarry dust to be mixed with red earth so as to have maximum shear strength is also determined. The shear strength of the mix was found from direct shear tests, and it was observed that there is a reduction in the shear properties when quarry dust was mixed with red earth. However, quarry dust can be a sustainable solution to sub-base stabilization especially in case of highways.

Neba C. Tony, G. Devdas, Sandra G. Raj, Renjitha Mary Varghese

Effect of Placement Moisture Content on Swelling–Shrinkage Behaviour of Expansive Soil

Rapidly increasing infrastructural activities across the world demand suitable land for founding the substructure. The coming era shall face trouble both with the scarcity of suitable land as well as challenges to deal with the existence of problematic soils at the site. Volumetric changes in the form of swelling and shrinkage with moisture variation are most commonly observed in expansive soils. Large damage/distress to the infrastructure founded on this type soils has been observed. Understanding of swelling and shrinkage of expansive soils with moisture variation is of primary importance. This paper presents an experimental study on determination of swelling–shrinkage and its variation with time and placement moisture content. An experimental setup has been designed and developed to accommodate three soil samples of 100 mm diameter and 100 mm height and swelling pressure measurement through constant volume method. Soils were procured from Delhi–Mumbai Expressway site near Ankleshwar, Gujarat, which was later aired dried and pulverized. Soil samples were prepared at three different preparation moisture content (i) at optimum moisture content, (ii) 5% on the dry side of optimum and (iii) 5% on the wet side of optimum. Experimental findings revealed maximum swelling pressure generation within first 24 h after commencement of the experiment. Swelling pressures of 41.8 kPa, 59.44 kPa and 23.22 kPa were observed for specimen prepared at optimum moisture content, at 5% dry side of optimum and 5% wet side of optimum, respectively. While swelling pressure found to increase till seven days, though at a lower rate, observed swelling pressure values were 55.73 kPa, 83.6 kPa and 37.25 kPa for specimen prepared at optimum moisture content, at 5% dry side of optimum and 5% wet side of optimum, respectively. The % shrinkage area were found as 22%, 33.8% and 15.2% for the samples prepared at OMC, WSO (OMC + 5%) and DSO (OMC-5%), respectively.

Arshad K. Siddiqui, Trudeep N. Dave

Foundation Bearing Capacity Estimation on Rock-Mass Using Hoek–Brown Failure Criterion and Equivalent Mohr–Coulomb Parameters

In general practice, the shallow foundations serve as economic and reliable solution to support high-rise buildings, bridges, and other heavy structures constructed on rock-mass. The aim of the present study is to simulate fractured homogenous rock-mass in finite element framework and to obtain bearing capacity of a strip footing. For this purpose, both displacement-based finite element (FE) analysis and finite element limit analysis (FELA) are carried out and results are compared. Finite element models of the flat rock-mass with supported foundations are developed in finite element package ABAQUS. The foundation is modeled using two-node cubic beam (B23) and rock-mass using plane-strain quadratic (CPE8R) element with reduced integration, having “Equivalent Mohr–Coulomb parameters.” Models with the same rock and foundation properties are modeled in OptumG2 based on FELA to obtain the upper-bound (UB) and lower-bound (LB) solutions with a constitutive model based on the Hoek–Brown failure criterion. The comparative study illustrates the critical issues that arise while implementing the failure criterion using the equivalent Mohr–Coulomb parameters, particularly in bearing capacity estimation, where the overburden pressure is low.

Shikhar Prakash, Dhiraj Raj, Yogendra Singh

Carrying Capacity of Model Steel Pile Foundation with Different Cross-Sectional Shapes in Sand

In present time, the steel piles are widely used for foundation of various structures constructed onshore and offshore. They are getting popularity because of easy availability, handling and splicing, and also durable. In the present investigation, the load-carrying capacity was compared of model steel piles having different cross-sectional shapes under vertical load in sand by keeping the equal cross-sectional area and equal length of pile. For this purpose, model steel piles of different shapes, i.e., solid circular, hollow circular, L-shaped, and H-shaped pile having equal cross-sectional area (A = 1.767 cm2) and equal embedded length 30 cm and total length of 33 cm were used. For this work, the effect of shape of single model pile and model pile group of 2 × 2 with spacing 3d, 4d, 5d on load-carrying capacity was studied in sand of two different relative densities under vertical load. For experimental work, circular tank of diameter 90 cm and height 60 cm was used and natural Bahadarpur sand near Sankheda, Vadodara district of Gujarat having angle of internal friction (φ) = 34• and density (ρ) = 1.687 g/cm3 (60% relative density) and angle of internal friction (φ) = 40• and density (ρ) = 1.747 g/cm3 (80% relative density) was used. The load was applied at the center of pile cap through jacking mechanism and pile cap was kept 3 cm above the soil layer to neglect the effect of cap in the capacity of pile. From investigation of results, it has been observed that the load-carrying capacity of H-shaped single pile is more as compared to all other cross-sectional shapes in 60% as well as 80% relative density. In pile group, all shapes of pile show an increase in load-carrying capacity with an increase in spacing from 3d to 4d and 5d but capacity trend is different in H-shaped pile as here the load capacity decreases with increasing spacing in both 60% and 80% relative density. Consequently in pile group the hollow circular pile shows maximum capacity with increasing spacing and relative density.

Khushal Paliwal, Nitin H. Joshi, Pooja Bhojani

An Experimental Study of the Piled Raft Foundation Subjected to Combined Vertical and Lateral Load

1-g experimental tests have been carried out to investigate the behavior of piled raft foundation subjected to combined vertical and lateral load. The vertical load was applied till a constant settlement of test models and it was followed by the horizontal incremental load. The piled raft models including a single pile, unpiled raft, and pile group models had been tested on cohesionless soil. The pile configurations of 2 × 2 and 3 × 3 with a constant spacing of 3.5 times diameter of a pile and constant pile length of 25 times diameter of a pile were adopted for the piled raft models in this study. The raft-soil contact was an important factor to reduce the horizontal displacement of the piled raft. There was a significant reduction found in the horizontal displacement of the piled raft foundation due to the presence of the vertical load. At an assumed horizontal load of 100 N, there was about 3.75–5.33 times reduction in the horizontal displacement of adopted piled raft models in the presence of vertical load till 10 mm settlement.

Uttam Kumar, Sandeep A. Vasanwala

Bell-Shaped Anchor with Geotextile Ties Embedded in Clay—A Numerical Study

A parametric numerical simulation has been carried out to study the behavior of bell-shaped anchor with and without geotextile ties within clayey soil. The study has been done with help of FEM software ABAQUS. Three types of soil and one typical model of belled anchor with diameter 0.125 m have been considered for the numerical analysis. Properties of geotextile sheets and soil mass have been studied and reported in the present work. Variation of uplift capacity with different parameters such as embedment ratios (H/D) of anchor, and cohesion of soil have also been studied. In the numerical study, weight of the soil as well as gravity has been taken into account. A sensitivity analysis and a mesh convergence study also have been performed to determine the model dimension and meshing criteria. Breakaway condition has been adopted here as no resistance is acting below the anchor against the soil mass. Both the anchor and the geotextile sheet as linear material and clay mass as elasto-plastic material have been considered in the analysis. With introduction of geotextile tie to the anchor, the uplift capacity of anchor with tie increases. Optimum value of Lg/D (Lg-diameter of geotextile sheet) is found to be 3 from the current investigation. Optimum numbers of geotextile tie layers are found to be 3 for a specific type of soil. Stress profile also has been plotted to identify the maximum stress in geotextile.

Arya Das, Ashis Kumar Bera

Studies on Tilt of Closely Spaced Strip Footings on Unreinforced and Reinforced Sands

Two or more strip footings are quite often built close to each other, due to which there will be overlapping of stresses in zones or at points between the footings. There is a non-uniform pressure distribution in the foundation soil beneath the footings, in the space between the footings and beyond. There is also an increase in confining pressure of the soils between the footings. All these result in the tilt of the footings. This numerical study looks into the tilt of the already existing strip footings due to the construction of an adjacent new strip footing on the surface of cohesionless soils. A parametric study is conducted including the effect of geogrid reinforcement/s beneath the new footing. One of the footings representing an already existing foundation is loaded with half of the estimated failure load of a single-strip footing, and adjacent new strip footing is loaded up to failure. The property boundary line is assumed to be midway between the two footings. Geogrid reinforcement layers beneath the new footing are considered to be extending equally beyond the footing on either side, up to the property line. Both unreinforced and reinforced sands are considered beneath the new footing for analyses. Tilts are observed to increase with the width of footing. At closer spacings, tilt was found to be more in case of loose sand. Results of this study indicate that there is a considerable increase in the tilt of the old footing in the presence of reinforcements beneath the new footing.

S. Anaswara, R. Shivashankar

Experimental Evaluation of Failure Zone in Sand Beneath the Ring Footing and Cutting Edge of Open Caisson Using Image Analysis

The analytical evaluation of the bearing capacity of the ring footing and cutting edge of the open caisson requires a definition of the size of failure zone in the soil, whereas the failure zone in soil depends on the type of soil and the configuration of the ring footing and cutting edge of the open caisson. In the study, the 1 g model tests are carried out to evaluate the failure zone in the sand beneath the ring footing and cutting edge of the circular open caisson. The radii ratio of the ring footing and cutting edge of the open caisson models are varied as ri/ro = 0.615, 0.737, and 0.783, and the tapered angle of cutting edge models is varied as β = 30° and 45°. The radius ratio is the ratio of internal radius to the external radius of the ring footing and cutting edge of the open caisson. The ring footing and caisson models are fabricated using Teflon tubes, and Indian standard sand is used as soil medium. The image-based deformation measurement technique is used to evaluate the failure zone in sand. The image analysis results are validated from the rigid displacement test.

Jitesh T. Chavda, G. R. Dodagoudar

Influence of Soil Variability in SPT Data for Predicting the Bearing Capacity of Piles

Standard penetration test (SPT) is one of the most commonly adopted methodologies to determine the soil profile at any particular site for calculating the bearing capacity of the pile foundations. Soil variability is inevitable. In this regard, the present study focusses on the statistical process of characterising the same based on the SPT data. This data was obtained from 20 boreholes at a site in Kolkata, which is proposed to adopt pile foundation for its upcoming structures. The vertical variability is characterised by a probability density function. The statistics of vertical variability comprising of mean and standard deviation are calculated, and the scale of fluctuation using the random field theory is obtained. The range of scale of fluctuation is found to be in good agreement with the globally accepted literature. This variability has been incorporated in predicting the bearing capacity of the piles for the proposed site using different correlations given by Meyerhof (1956), Aoki and De’Alencar (1975) and Decourt (1995).

Kotra Saikumar, Kaustav Chatterjee

Nonlinear Analysis of Laterally Loaded Pile Group in Layered Soil–Ash Deposit

The current scenario for the geotechnical engineering is not only to take care of vertical load of superstructure impending to the soil but also the lateral load subjected to the structure must be taken into consideration for the safe design of foundation. For designing pile foundation, knowledge of load–deflection behavior of pile under moderate to heavy load is necessary. In the present study, numerical analysis of pile group in a layered soil–ash system has been performed using SoilWorks software. The analysis is based on P-Y curve method which is a realistic and practical method for the load deflection analysis of pile under lateral loads. The pile arranged in grid form in 3 × 3 and 4 × 4 pattern. The influence of pile diameter effects along with various pile spacing on the behavior of the pile–soil system has also been studied. The stability of pile was checked under horizontal and vertical condition. The pile group has been analyzed with vertical load, lateral load, and moment at the top end of the pile. The response of the pile includes horizontal displacement, shear force, moment, and ground reaction along the pile length.

Amit Kumar Ram, Supriya Mohanty

Rationalization of LRFD Method for Safe Bearing Capacity of Shallow Footings to Incorporate the Type of Shear Failure

The geotechnical design philosophy is in the transformation stage to implement load and resistance factor design (LRFD). IS 6403 uses working stress method to calculate safe bearing capacity for shallow foundations, while Euro Code 7 and AASHTO use the LRFD method and provide guidelines for proportioning shallow foundations using partial safety factors. Hence, in order to adopt the LRFD design method, it has to be rationalized to have the convincing bearing capacity with respect to IS Code results to incorporate the shear failure criteria. In present work, safe bearing capacity for shallow footing is calculated as per IS Code, Euro Code 7 and AASHTO by taking the variations in shear failure criteria, i.e., with and without consideration of shear failure criteria (only for Euro Code design), soil parameters (cohesion, C and angle of internal friction, ϕ), size and depth of footing. Problems are then identified by checking the consistency of results obtained by Euro Code 7 and AASHTO with respect to IS Code results. Further, as a part of rationalization, the recommendation is given that in Euro Code 7 design, the partial safety factors must be applied to bearing capacity factors, instead of applying to soil properties (C, ϕ). Also, net safe load (kN) obtained from AASHTO is on lower side as compared to IS results because it considers higher average FOS than IS Code.

Ronak Kotadia, K. N. Sheth, Avani Malaviya

Case Study on Underpinning of Foundation for an Industrial Building Renovation

Underpinning involves strengthening of foundation for existing structures using various methods. One of the suitable methods is adapted according to the subsoil and site conditions. One such method is extending the dimensions of existing foundation to rest under supportive soil strata. This method is effective in renovation of existing buildings where more space is available for working condition and requires skilled manpower. This paper deals with a case study on underpinning for an industrial building at Virudhunagar, Tamil Nadu, India. Since there is a need for a conversion of an existing spinning mill to an industrial plant, the necessity for strengthening the existing structures was proposed. The suggested method of underpinning by extending the breadth and depth of existing foundation was carried out and the outcome proved to be successful.

A. Karthikeyan

Evaluation of WSM, LRFD and FE Methods for Pile Capacity Calculation with Pile Load Test for IGM

As many infrastructures, projects are going on in Ahmedabad like metro rails and bridges which are being constructed, for that behaviour of pile foundation capacity is must, and in that too the behaviour of pile in overconsolidated soil. Sometimes the overconsolidated soil is considered as intermediate geomaterials (IGM); i.e. behaviour comes in between the continuum of soil and rock. There are many analytical methods for evaluating pile capacity in any type of soil. But for overconsolidated soil, it may be exhibited the wide range of properties. Using an analytical method, 17 problems were analysed and there results were calculated from LRFD method (O’Neill and Reese) and IS code (IS 2911 P1/S2, 2010) were compared, and the FEM modelling of this soil was done using software PLAXIS 2D. The load settlement curve from FEM software and actual load test data were super-imposed, and the result was quiet matching. Skin friction was found to be over predicted by 37.26%, 212.37%, and 32.46% when determined from static formula (IS 2911 P1/S2, 2010), Cole and Stroud method (IS 2911 and IRC 78, 2014) and LRFD method (O’Neill and Reese), respectively. End bearing was found to be over predicted by 754.31%, 864.89%, and 55.04% when determined from static formula (IS 2911 P1/S2, 2010), Cole and Stroud method (IS 2911 and IRC 78, 2014) and LRFD method (O’Neill and Reese), respectively.

Pratik V. Shah, Kandarp K. Thaker

Analysis and Design of Micro-pile Foundation for an Extension of a Commercial Building

Foundations are classified as shallow and deep. They provide support for superstructure by transferring load to layers of soil or rock that have sufficient bearing capacity. However, certain ground conditions and site constraints make it difficult to use these conventional foundations. In such situations, micro-piles are seen as the only alternative. They can be used both as a ground improvement method and structural element designed as soil frictional piles and rock socketed piles either under tension or compression. They can be installed in restricted access sites making it very favorable. The present paper is a case study of use of micro-pile for a commercial building at Chhattisgarh, India, where the access to the construction site is restricted and the ground conditions are unfavorable for conventional foundations. The geotechnical design of micro-pile is carried out. The present paper also discusses the design of group of six micro-piles with a pile cap which were modeled in Plaxis 3D according to substrata conditions observed at a construction site and the deflection parameters were observed.

Rutuj Chheda, Atharva Pisolkar, Chhaya Kandpal, Jigisha Vashi, Aditya Soni, Rishabh Bakliwal

Experimental and Numerical Investigation of Combined Batter Pile–Raft Foundation Embedded in Sand

A geotechnical composite foundation system named combined pile–raft foundation (CPRF) is widely used in buildings experiencing colossal loads. Even though raft foundation reduces differential settlement, it tends to cause excessive settlement which can be subsided by using piles. Batter piles are deliberately known for their lateral resistance compared to plumb. The response of CPRF with batter pile under horizontal loading needs enhanced studies. This research focusses on the parametric configuration of combined batter pile–raft foundation embedded in sand. The effect of direction of batter and the angle of batter is studied experimentally under constant relative density. For experimental investigation, model test tank was used and 2 × 1 solid steel piled raft model was fabricated and used. The basic parametric configuration chosen for the combined batter pile–raft foundation is L/D—20, S/D—3 and diameter of pile and thickness of the raft was taken as 10 mm. The model is numerically simulated in a comprehensive three-dimensional finite element software ANSYS. The results of the experimental investigation and the numerical simulation are compared. The efficient direction of batter was found to be negative and was carried over for the further studies. The angle of batter taken for the study was 10°, 15°, 20°, 25° and 30° in-battered. The optimum batter angle was found to be in the range from 15° to 20° in-battered. The results from the numerical investigations were found to be in accordance with the experimental results.

M. Mahalakshmi, B. Soundara, C. D. Hashini

An Analytical Parametric Study on Behaviour of Flexible Raft Foundation

The understanding of soil–foundation–structure interaction is important for design of flexible raft foundation. For flexible foundation, the behaviour would be influenced by the loading as well as the foundation and soil parameters. The present study attempts to understand the influence of the parameters such as meshing size, loading intensity, magnitude of modulus of subgrade reaction (Ks) and raft thickness on base pressure and settlement of flexible raft foundation using STAAD Pro. A symmetrical multi-storeyed building with 25 columns along with raft foundation has been modelled. The building height is varied as 3-storeyed, 6-storeyed and 10-storeyed to simulate different loading intensity and raft thickness is varied as 0.5 and 0.9 m to understand effect of raft rigidity. Ks values of 2000 and 12,000 kN/m3 have been considered for the study. Study concludes that 0.5 m mesh size can be utilized for practical foundation modelling purposes. The effect of Ks on base pressure and settlement variation is more prominent as compared to thickness of raft foundation. Further, the base pressure and settlement increase linearly with increase in storey height. The study presents useful guidelines for the foundation engineers for design of flexible raft foundation.

Pritam Sinha, Ram Wanare, Parishi Dalal, Kannan K. R. Iyer

A Case on Engineered Solution for Deep Excavation in Restricted Space

This paper discusses the methodology adopted in soil support for deep excavation carried out for installation of press foundation in live working mechanical shop with space restriction and variable soil conditions. The method adopted was the cheapest of available alternatives.

Ajitkumar Kumbhar, Rajay Balwan, Girish Gokhale

Response of Laterally Loaded Monopile Using Three-Dimensional Finite Element Analysis

The increase in need for energy in the developing world boosted the search for efficient energy sources. Most of the current energy sources in the past decades were not sustainable. The growing concern on the existence of earth leads to find an alternative sustainable energy source. The right proportion of energy need in many developed countries is obtained using offshore wind energy. Offshore wind turbine (OWT) produces renewable and efficient energy in this era, which is supported on large-diameter monopiles. These monopiles are subjected to very high lateral and moment loads. This paper deals with the response of a bottom fixed monopile under lateral loads taking into account varying soil strata and pile diameter. The analysis was performed using a three-dimensional finite element approach for the pile embedded in three types of soils, that is, clay, sand, and layered soil. By varying the diameter of the monopile, it is observed that large-diameter monopile in any soil tends to behave like a rigid system having a minor deflection. However, the soil profile influences the behavior of monopile considerably with considerable length to diameter ratios.

Jithin P. Zachariah, Jagdish Prasad Sahoo

Influence of Combined Vertical and Lateral Loading on Lateral Response of Piled Raft Foundation

Due to the complexity involved in analysing the piled raft foundation under combined loading, the existing design practice for the piled raft assumes that the influence of vertical and lateral loads is independent of each other and the experimental tests on the behaviour of piled raft foundation under the action of combined vertical and lateral loads are relatively scarce. Therefore, the objective of the present study is to examine the behaviour of piled raft foundation subjected to pure lateral loads and combined vertical and lateral loads through laboratory model tests. The experimental programme includes the prototype model test on raft braced by 2 × 2 and 3 × 3 pile groups. The laboratory tests are performed in silty-clay soil underlain by sandy soil. Initially, the response of the piled raft foundation under pure lateral load is performed through laboratory model test and to understand the response of the piled raft foundation under combined loads, and the influence of vertical loads equal to 0.25Vu, 0.5Vu, 0.75Vu and 0.9Vu are considered. The ultimate vertical load capacity (Vu) corresponding to the settlement of 10% of raft width is evaluated by a separate vertical load test. The results of the experiments have shown the significant influence of vertical loads on a pile’s lateral response. For the structural design of piled raft, it is important to find out the bending moment developed in the pile in piled raft. Therefore, the influence of combined loading on the bending moment developed in the pile has been examined from the laboratory model test.

Plaban Deb, Sujit Kumar Pal

Interpretation of Load-Settlement Curves from Graphical Methods

Bearing capacity of pile depends mainly on the type of soil through which it rests and on the method of installation. Many empirical and analytical formulae developed based on the field and laboratory experiments to estimate the pile group bearing capacity. The present investigation is carried out to get the load-settlement characteristics of different configurations of pile groups, such as 1 × 1, 2 × 2 and 3 × 3. In many projects, some of the manufactured piles are loaded to determine the pile bearing capacity. This is the most reliable way to determine the pile capacity. However, it is not easy to determine the point where the pile has reached its ultimate capacity on the load-settlement curve. By using different graphical methods, the ultimate bearing capacity is calculated from load-settlement data. Among these methods, there are considerable differences between the graphical ultimate bearing capacities of the piles which decrease to 35% for the piles loaded up to the collapse load and increases up to 120% for the piles loaded to the failure load. Improvement ratio and settlement ratio are calculated using load-settlement curves. Model plate load test is used to determine the load-settlement curves. It is time and cost efficient, easy to perform and reliable. Experiments are conducted on dry, clean and poorly graded sand. Steel pipe piles of length 30 cm, diameter 2 cm, 2.5 cm are used in this experiment. The spacing between the piles is taken as 3d.

Naga Sireesha Ghanta, Sujit Kumar Pal

Behavior of Rigid Footing Rested on a Group of Stone Column

Raft foundation often adopted for structures constructed on highly compressible soil. Sometimes raft footings are preferred on stone column-improved ground. The current FEM-based numerical study investigated the behavior of a rigid square footing model resting on the surface of a soft ground improved with a group of stone column. To analyze the behavior of the rigid footing, a group of fully penetrating stone columns was constructed beneath the rigid footing. Various parameters such as area replacement ratio, column spacing and relative position of column have been studied. Performance of rigid footing enhances with the increment of area replacement ratio. Bearing capacity improvement was found to be higher at lower settlement level. And a better settlement improvement was observed when footing is acted upon by a higher loading. For larger size raft footing, stone columns arrangements have a significant effect on load-settlement behavior. When stone columns are placed near to the center of the footing, it shows a better improvement in term of settlement and load carrying capacity. A single stone column of equivalent area ratio constructed at the center shows similar behavior as a group of stone column. Different types of failure mechanism were observed for the stone columns placed at different position. Stone columns constructed near the edge of the footing failed by the combined action of bulging and buckling. Whereas, central columns mainly failed by bulging near the top.

Mrinal Bhaumik, Suresh Prasad Singh, Megha Biswas

Design and Construction of Rock Socketed Pile Foundation for Bridges—Case Study on Road Project in Madhya Pradesh, India

The design and construction of rock socketed pile foundation involve finalization of required length of rock socket based on the detailed study of the founding rocky strata and also include the establishment the safe load carrying capacities of pile foundations corresponding to its rock socket. Such detailed assessment of safe and allowable load carrying capacities of rock socketed bored cast-in-situ pile foundations is done for the new widened bridges of four-lane configuration along the project corridor in between Biaora and Dewas section of NH3 in the state of Madhya Pradesh. Those bridge structures along the project road are founded over the bored cast-in-situ concrete pile shaft which was penetrated through the overburden soil layers and then finally socketed inside the underlying highly to moderately and slightly weathered basaltic rock of varying depth. This paper presents the above-said typical project case study on the details of geotechnical design assessment of rock socketed pile foundation covering its safe vertical and lateral load carrying capacities for the bridges. The different types of field load test namely “Vertical and Lateral Pile Load Tests” over the “Test Pile” and “Working Pile” are conducted to establish the estimated safe load carrying capacity of rock socketed pile foundation. The results of these pile load tests are also reported here in this paper. The required “Pile Penetration Ratio (PPR)” of the desired socket length inside the founding rocky strata is fixed based on the nature of rock as explored through investigation. This pre-decided “PPR” is adopted during installation of pile foundation inside the underlying rocky strata.

Avik Kumar Mandal, S. Sailesh, Pradyot Biswas

Evaluation of Bearing Capacity of Ground in Transition Zone

The determination of ultimate bearing capacity in transition zone by classical theory is not clearly explained (IS: 6403-1981: Code of Practice for the Determination of Bearing Capacity of Shallow Foundation, first revision, New Delhi, 1981 [1]) (Murthy in Soil Mechanics and Foundation Engineering. Marcel Dekker Inc. New York [2]; Punmia and Jain in Soil Mechanics and Foundations, 17th edn. Laxmi Publications, New Delhi, India [3]). Most of them including IS: 6403-1981 suggest a linear interpolation between general and local shear failure in transition zone with no further explanation. Practicing engineers do not have consistency in calculation of bearing capacity in the transition zone. More often, they are likely to encounter the situation of the angle of internal friction lying between 28° and 36°. Many a times, it is felt that the baring capacity is overestimated. Therefore, an attempt is made in this paper to determine the ultimate bearing capacity by different methods in the transition zone and to give more precise calculation procedure for the determination of bearing capacity in the transition zone. For this purpose, Terzaghi’s bearing capacity factors are used in the analysis. An attempt is made to present bearing capacity factors as a function of angle of internal friction of soil considering local shear zone, transition zone and general shear zone. Three methods to determine the ultimate bearing capacity of soil in transition zone are discussed, and their relative conveniences are brought out.

Sreevar Ramesh, R. V. Suman, M. Yashwanth, S. K. Prasad

Behavior of Rectangular and T-Shaped Diaphragm Wall Panels in Mixed Soil Conditions: A Case Study

In urban areas, properly designed deep excavation support systems are essential for any new underground construction adjacent to the existing buildings. Diaphragm walls are widely used in India as deep excavation support system to facilitate strut-free excavation as well as to limit the soil movement of surrounding areas due to excavation. In this paper, a ten-story new commercial development required a three-level basement excavation of 12.5 m (max.) from the existing ground level (EGL). Project site consists of mixed soil condition with silty clay of varying consistency followed by dense sand underlain by a weathered rock layer. A 600 mm thick rectangular D wall panel with temporary ground anchors was used to support deep excavation wherever sufficient setback is available. In the same site, one of the corners has a restricted setback which demanded 8 m cantilever wall with high structural rigidity. Hence, T-shaped diaphragm wall panels of 600 mm thick were adopted as a permanent cantilever wall. Numerical modeling of the retention system was analyzed using WALLAP and PLAXIS 2D software. The wall deflections were monitored through inclinometers. This paper reviews the performance of cantilever diaphragm wall and rectangular panel wall with single anchor for 8 m excavation depth. Cantilever T-shaped diaphragm wall proved to be effective and stable system, where tie back is not feasible.

C. Vimala, Madan Kumar Annam

Bearing Capacity of Eccentrically Loaded Circular Footing Supported on Reinforced Sand

In the recent past, investigators have given less attention on circular foundation. Thus, this research deals with the strength of circular foundation on reinforced sand. There are total 48 numbers of tests conducted on model footings of radius 10 and 5 cm and eccentricities varying from 5 to 15 mm with an increment of 5 mm. Square shaped geonet is used as reinforcing material having aperture size of 1.637 mm. There are three layers of reinforcement used, i.e., from 0 to 2, where the distance between reinforcing layer and base of foundation is 0.35D and distance between two reinforcing layers is 0.25D. The test tank has size of 0.60 m × 0.60 m × 0.30 m. This test is carried out on dense and medium dense sand. Relative density is 71% for dense sand and 51% for medium dense sand, calculated as per IS code method. Load-settlement curve of each experiment is done from which bearing capacity is calculated by tangent intersection method. The result showed that rise in reinforcing layer increases the bearing capacity, whereas rise in eccentricity has decreased bearing capacity. The results are also compared with different existing theories, with unreinforced and reinforced dense and medium dense single entities and bearing capacity ratio (BCR) which are calculated.

Srikalpa Rajguru Mahapatra, Rupashree Ragini Sahoo

Seismic Bearing Capacity of Shallow Footing in Layered Soil

Ultimate bearing capacity of a footing resting on a stratified deposit reduces under a seismic excitation as soil stiffness degrades during a shaking. Ultimate bearing capacity depends on the shear strength parameters (cohesion and angle of internal friction) of subsoil, along with shape and size of footings. An attempt has been made to study the bearing capacity of shallow circular and strip footings in a layered cohesionless soil under static and seismic conditions. The subsoil conditions resemble that of a site located at Rajarhat, Kolkata, West Bengal, India. The modeling has been done using finite element method. The analysis has been carried out for footing width (B) of 2.0 m and depth (Df)-to-width ratio (Df/B) of 0.5 and 1.0. For each Df/B ratio, the analysis has been repeated for three different ratios of layer thickness [top layer (weaker): bottom layer (stronger)] which are 0.33, 1 and 3. For seismic condition, pseudo-static analysis has been performed for horizontal seismic acceleration 0.1–0.3 g. It has also been confirmed from the initial evaluation of liquefaction potential based on the SPT data for the site that the cohesionless soil layers considered here are not prone to liquefaction. It has been observed that due to variation of layer thickness ratio from 0.33 to 3, the ultimate bearing capacity decreases up to 20.00% under static case, whereas for seismic case, decrement of bearing capacity is about 18.00% under similar condition. It has also been found that with the increase in horizontal seismic acceleration from 0.1–0.3 g, the seismic bearing capacity factors Nq and Nγ reduce appreciably by 30% and 60%, respectively. Further attempt has been made to find the effect of shape of footing on seismic bearing capacity. The paper presents the importance of seismic effect, on layered soil and shape and size of footing in terms of ultimate bearing capacity.

Smita Tung, Sibapriya Mukherjee, Narayon Roy, Somenath Mukherjee

Ground Improvement by Granular Anchor Pile Foundation in Cohesive Soil Under Axial Pullout Loads

Due to rapid urbanization and increase of population, the demand of construction has increased significantly during the last few decades and thus resulting in scarcity of land. So, to eradicate this problem, geotechnical engineers are using several ground improvement techniques such as use of geosynthetics, stabilization of soil, vibro-compaction, stone column, blasting, compacting piles and granular anchor pile foundation to construct buildings on weak subsoil strata for the optimum usage of land. These techniques are used to improve the soil bearing capacity to withstand compressive as well as uplift forces imposed on the structure. The adoption of suitable type of foundation technique will depend upon various factors such as nature of soil, type of loading and type of structure. Granular anchor pile foundation is the innovative technique used to sustain the compressive and pullout loads over weak subsoil. In this paper, the laboratory experiments were conducted to understand the behavior of axial pullout load of granular anchor pile foundation in cohesive soil. The parameters studied were length of the pile, diameter of the pile, L/D ratio and size of the granular fill material. The test results indicate that the pullout capacity decreases with the increase in L/D ratio from 7.5 to 12.5. There was an increase in the pullout load resistance, when the diameter of the pile increases. Moreover, pullout load capacity increases when size of the granular fill increased.

Heena Malhotra, Sanjay Kumar Singh

Seismic Bearing Capacity of Strip Footing Embedded in Slope Situated Below Water Table

An attempt is made to give a formulation of the pseudo-static bearing capacity coefficient of a shallow strip footing embedded in slope in c-φ nature of the soil in terms of a single coefficient (Nγe) using limit equilibrium method which is subjected to groundwater flow. Failure surface is assumed linearly varying with cohesion, surcharge and unit weight of the soil. Iteration technique has been applied to optimize the solution. The ultimate bearing capacity equation was derived as a function of different properties of soils and footing, i.e., width of footing, depth of footing, the cohesion of soil, unit weight of soil and depth of water table. Various parametric studies have been studied to show the variation of bearing capacity coefficient with different parameters. Design chart of table has been shown for various ranges of parameters.

Litan Debnath, Rohan Deb, Prasanta Das, Sima Ghosh

Study on Piles Subjected to Axial and Lateral Loading

Piles are often subjected to combination of vertical and lateral loading in places like bridge piers, offshore structures, retaining walls, etc. The behaviour of piles under biaxial loading is much more complex when piles are embedded in layered soil system. In this paper, an attempt is made to study behaviour of pile subjected to vertical and lateral loading for varying soil layers. Model pile load tests have been conducted in a model tank filled with sand, clay and clay–sand medium to examine the behaviour of single pile and pile group under vertical and lateral loading. Both single and pile group (2 × 2) have been subjected to axial compressive loads and lateral loads, for varying type of soil medium, combinations of loading, number of pile and L/D ratio. Result indicated that the vertical load capacity of pile increases with L/D ratio and number of piles at any given settlement, but however, the vertical capacity of sand medium is always higher compared to clay or clay–sand medium. Similar trend is observed on the lateral load capacity also. At the given deflection, lateral capacity increases with L/D ratio and number of piles relatively on the higher magnitude for sand medium but less noticed for clay and clay–sand bed. Under the influence of ultimate vertical load, the lateral capacity of pile is much lower than the lateral capacity of pile without vertical load, for single pile irrespective of the settlement and for pile group at specified settlement values.

V. K. Stalin, A. Priyadharshini, P. Deepan, A. Abudaheer

Experimental Study of Pile Resting on Sloping Ground Subjected to Cyclic Lateral Loading

Pile foundation has to resist lateral loads coming from moving trains, winds, etc. Due to presence of sloping ground, there is reduction in lateral capacity of pile because of reduction in passive resistance offered by soil. The nature of forces is dynamic, and a very limited study has been done to determine the effect of dynamic lateral loading on piles resting on sloping ground. In present study, small-scale physical model tests were performed on sand to determine the reduction in lateral capacity of pile when subjected to 50 numbers of cycles. The relative density (30% and 60%) and ground slope (0° and 20°) were the variables. Initially, the static lateral capacity was determined for both the horizontal and sloping grounds. The load corresponding to 5 mm lateral displacement is the lateral capacity of pile. In second phase, cyclic loading was given to the pile and after that its capacity was determined same as in static case, and the results were compared. In static case due to presence of slope, only the reduction in lateral capacity is 20%–30% depending on the relative density. Due to application of cyclic loading, the reduction in lateral capacity was greater than 50%. This study shows that pile resting on sloping ground and subjected to cyclic lateral loading becomes critical case and needs to be considered while designing pile foundation.

Dinesh Bishnoi, M. Upendra, Jignesh B. Patel

A Study of Piled Raft Foundation

Nowadays, piled raft foundation is increasingly being used not only in developed countries but also in developing countries like India. This paper is based on the study of piled raft foundation constructed in Uttarakhand, India, with the help of finite element software ELPLA and finite difference software GROUP. In analysis with ELPLA methods considered are linear as well as nonlinear methods such as hyperbolic stress–strain function and method as per DIN (4014) standard. The software is validated with results of the on-site pile load–settlement test conducted on individual pile. The results are compared also with analysis performed using PLAXIS 3D.

Riddhi M. Gupta, Jaykumar C. Shukla, Nitin H. Joshi

Seismic Stability of Unsupported Conical Excavation in Clayey Ground

Conical excavations without support are often made in some field projects, such as foundations for piers, oil and water tanks. The seismic stability of these excavations has been given least importance in the research field. The instability of these unsupported excavations might increase during a seismic event. Hence, a realistic estimation of the seismic stability of unsupported excavations is a prominent issue, especially for the perpetual purpose. In the present study, seismic stability number for unsupported excavations has been proposed using the finite element (FE) analyses. Due to symmetry in the geometry about the vertical axis, axisymmetric FE models have been developed using OptumG2 software based on the finite element limit analysis approach. The soil (clay, with isotropic and constant undrained shear strength property) has been modelled as a perfectly plastic Tresca material following an associated flow rule. Boundary conditions were considered as per the field conditions, and seismic loads were considered as pseudo-static force applied in terms of horizontal seismic coefficient, αh. Adaptive meshing technique was adopted to predict the results reasonably closer to exact solutions. The seismic stability of these conical excavations is reported in terms of stability number. Moreover, the effects of depth of excavation, inclination angle, intensity of seismic loading, etc. on the seismic stability number are explored in detail. For deeper insights and influence of various affecting parameters, non-dimensional design charts are presented. Further, it has been observed that the considered parameters have significant effects on the seismic stability of conical excavations.

Dhiraj Raj, M. Bharathi, Sanjay K. Shukla

Analysis of Settlement Induced by Dissipation of Excess Pore Water Pressure Due to Piling in Soft Clay at Haldia

Consolidation settlement induced by dissipation of the excess pore water pressure due to pilling in soft clay and negative skin friction caused by it were analysed. Piling or the pile driving process usually induces excess pore water pressure in the surrounding soil. When this excess water pressure dissipates later on after the pile driving process is complete, settlement of the surrounding soil takes place and a negative skin resistance along the pile surface develops, which is undesirable (Hosseini & Rayhani in Int J Geo-Eng 2017) [5]. In this paper, PLAXIS 2D is used to take into account the nonlinear consolidation behaviour of the soil. The pile driving process was defined and analysed in terms of the expansion in a cylindrical cavity. In general, the results based on the FEM method were consistent with the actual field measurements on site. However in response to the problem, the permanent solutions are worked on.

Akanksha Kesharwani, Abhijeet Gupta, Ashok Kumar Khan

Performance Evaluation of Piles for Slope Reinforcement

Landslides are defined as the mass movement of materials down the slope under the force of gravity. The landslides can be initiated by various causes such as rainfall, earthquake, change in ground water level and increase or decrease in shear strength of slope materials. Occurrence of landslides always causes problems to the safety and security of people and infrastructure facilities. To mitigate landslides, various slope stabilization techniques such as provision of slope drainage, soil nailing, construction of piles and retaining walls, installation of slope anchor system and biotechnical slope stabilization were employed. In this paper, studies involving pile as a reinforcing member in unstable slopes were performed experimentally using large direct shear box (LDSB) apparatus. For experimental studies, two layers of clay soil having undrained shear strength 30 kPa representing unstable soil at top and 60 kPa representing stable firm soil at bottom were prepared. Experiments were then performed with and without pile reinforcement in soil. The unstable soil slope model was reinforced with single-, two- and three-pile group system with 2D and 3D spacing to evaluate the effect of reinforcement and improvement in shear strength of unstable soil. From experimental results, it was understood that when piles installed as a reinforcing member in soil slope, the installation improves the shear strength of unstable soil, minimizes slope movement and increases the factor of safety of the slope, thus improving the safety of slope against landslide hazards.

Dinesh Kumar Malviya, Ganesh Kumar, Madan Chandra Maurya

Stability Analysis of Soil Slopes Subjected to Foundation Loads During Earthquakes

The stability of slopes subjected to foundations loads near the top of the slope has been investigated in the present study. The c-ϕ soil slope with different width and embedment depth of foundation has been considered here. In the present study, the building load is considered as a surcharge load on the slopes. Strength reduction method has been adopted to investigate the variation of factor of safety (FOS) of slope against the different parameters of the imposed load and slope angle. The earthquake force has been considered as fixed body force within the soil mass. From this study, the FS decreases with the increase of building or foundation loads, and at a certain distance from the edge of the slope, the FOS remained constant. The improvement of FOS has been observed with the increase of embedment depth of footing for all surcharge loads. The rapid reduction of FOS has been noted when foundation load is increased on slopes in both static and seismic case.

Sukanta Das, B. K. Maheshwari

Probabilistic and Deterministic Analysis of Lungchok Landslide, South Sikkim, India

The northern part of INDIA is most vulnerable in failure of slopes due to hill region with complex geology, high-intensity rainfall and frequently occurrence of earthquakes. The stability of slopes has traditionally analyzed using deterministic methods. But uncertainty plays major role in geotechnical engineering. the probabilistic characterization of uncertainties in input variables for the assessment of slope stability is very helpful. In this paper, the safety of slope using deterministic and probabilistic methods under static and pseudo-static loads is carried for Lungchok landslide which is in south district of Sikkim state, India. The Factor of safety calculated by deterministic cannot represent the stability of slope exactly as it is limited to the single value of parameters. The stability of slope is independent of single soil parameter but dependent on random process with distribution of soil parameters. Rather than the conventional factor of safety against the sliding failure the probability of sliding failure is most useful. The stability of slope is analyzed using two approaches deterministic and probabilistic analysis under the effects of static and pseudo static forces. The deterministic approach with Morgenstern Price limit equilibrium method and the probabilistic approach with Monte Carlo simulation have been performed for the stability analysis of Lungchok landslide using Geo-Studio Software. The dependence and efficiency of the probabilistic strategies in the investigation of slope stability was highlighted in this paper.

Neharika Rao Ganta, Neelima Satyam

Experimental Study of Ugat Canal Soil for Slope Stability

Slope stability is one of the major aspects of geotechnical engineering and plays significance on large-scale infrastructure projects such as highways, railways or canals. Slope failure is the major problem in earthen canal due to seepage problem. Due to excess imposed loads, discharge forces, erosion and gravity forces, drainage and irrigation canals may suffer from a full or restricted slope failure. Side slope failures of irrigation at Ugat canal located near Jahangir Pura, Surat, will possibly suffer from heavy catastrophes with destructive damages to public lives and belongings. The reason of canal slope failure is due to piping in salt influenced or distributive soil, discharge forces in soft clayey or sandy soil, deficient standard of the soil mass mound same as in black cotton soil, i.e., soft clay or loose sand and accordingly dissolution due to immoderate use of irrigation water or utilizing surface irrigation method at places near to the bank. There is no generalized method of restoration for slope failures because of the distinctiveness of the attributes and situations of each site. Hence, based on characteristics of sites, each site needs to be studied individually. To prevent the failure, the side slope of the embankment is strengthened by coconut husk which reduces slope failure in earthen canal. There is significant increment in load carrying capacity of soil by adding coconut husk at various contents such as 0.5, 1.0 and 1.5% replacement by soil. At 0.5, 1.0 and 1.50% replacement, the strength increment is 1.52, 1.70 and 2.11 times of normal soil.

Yati R. Tank, Ashika S. Patel, Pratima A. Patel, Akhilesh R. Tank

Pseudo-static Stability Analysis of Multilayered Slopes Using Sarma’s Method of Non-vertical Slices

Stability analysis of multi-layered slopes with complex geometry and pore pressure conditions has always been a topic of immense interest to both the researchers and the practitioners in the field of geotechnical engineering. Over the decades, within the framework of limit equilibrium methods of slices, a number of rigorous methods have been proposed which are valid for general non-circular slip surfaces, satisfy all conditions of equilibrium, and take full account of the interslice forces. Among these, the Sarma method is the only method in which the slices are not necessarily vertical, and the critical inclinations of the slices are found as part of the solution and use the internal strength of material for the solution of the problem. Because of the number of iterations involved in finding the critical set of slice inclinations, Sarma method is not suitable for finding the critical slip surface. In order to compare the results obtained by using the other rigorous methods with those using Sarma’s method, the latter can be used to re-analyze the critical slip surfaces determined for the other methods. In this study involving three complex slope stability problems, the critical slip surfaces determined using the Morgenstern and Price method and the Spencer method are re-evaluated using the Sarma method. The GEO5 software is utilized for the purpose. The comparison of results has brought out that compared to the Sarma method, both the Morgenstern and Price and the Spencer method consistently yields conservative values of factor of safety for each of the three example problems.

Somenath Mukherjee, Subhadeep Metya, Gautam Bhattacharya

A Study on the Erodibility of Lateritic Soil Due to Flooding

Soil erosion is a process of detachment and transportation of soil materials from its original place by the action of various erosive forces. Erodibility of soils is referred to as the vulnerability of the soils to get eroded. Laterite soil is one of the major types of soil found in Kerala, which is rich in iron and aluminium content. So, the present study aims at identifying the key parameters affecting the erodibility of lateritic soils during floods as well as studying its effects on lateritic slopes. Also, the study focuses on the measurement of quantum of erosion by developing a suitable test set-up. The flood parameters are considered as the key parameters for the erodibility study. The test set-up consists of a tank with a lateritic slope inside, an inlet tank (storage tank) and a sediment collecting tank. Water is allowed to flow from the inlet tank towards the lateritic slope, and the water along with eroded soil is collected in the sedimentation tank after passing through a strainer. Tests are carried out under various flood parameters such as the velocity of flood water, the height of flood water and duration of water flow at a slope of 2.5:1 maintaining a bulk density of 18 kN/m3. The quantum of erosion is measured in terms of the total weight of the eroded material. The variations in the erosion rate under varying flood parameters are studied.

Zoheb Faisal, P. Muhammed Shibil, P. K. Jayasree, J. Jayamohan

Experimental Investigations on Rainfall-Induced Landslides

In recent times, the occurrence of natural hazards in India and around the world is increasing day by day. Landslides are one of the most destructive natural phenomena which not only cause extensive damages to the structures but also result in loss of lives. Among various factors, rainfall is one of the most important triggering factors for inducing landslides. In most of the time during rainfall, due to infiltration of water into the soil, the pore water pressure increases which destabilizes the slope resulting in landslide. This paper presents detailed laboratory experimental studies on the behaviour of rainfall-induced landslides. For experimental testing, indigenous test system has been developed at CSIR-CBRI for investigating rainfall-induced landslide. The system comprises a tilted channel and artificial rainfall simulator system. The arrangement of rainfall simulator can able to reproduce landslide triggering under varying intensities of rainfall with uniform rain distribution. For the present study, a model slope was created with the landslide debris soil material brought from the Lesser Himalayan region of Uttarakhand State. After soil characterization, rainfall experiments were conducted on the equivalent slope model using artificial rainfall simulator system. The rainfall experiments were performed with rainfall intensity equivalent to some reported high rainfall intensity experienced in the past in the Himalayan region. During rainfall experiments, the increase in soil moisture and soil movement was monitored continuously. The time at which slope failure initiated was observed and corresponding soil moisture and slope movement pattern was evaluated. Finally, the mechanism of slope failure was analysed and possible slope protection measures were suggested.

Ganesh Kumar, Shantanu Sarkar, Mayank Gupta, Priyanka Devi

Study on Stability Analysis of South Bank of River Brahmaputra and Its Tributaries in the Reaches of Upper Assam

This work presents the results of an investigation aimed at evaluating the stability of riverbanks along the Brahmaputra River and some of its Southern tributaries—Burhidihing, Disang, Jhanji, Bhogdoi and Kakodonga. Continuous erosion and failure of the alluvial riverbanks have led to serious loss of land, life and property, and an attempt has been made to address the same. Soil samples were collected from the seven riverbank sites and the geotechnical characteristics of the samples were determined. Stability analysis was carried out based on a Culman-type analysis of steep, cohesive riverbanks proposed by Osman and Thorne (J Hydraul Eng, ASCE 114(2):134–150, [1]). The riverbank stability is checked for bank angles ranging from 60° to 85°. Critical bank angles are determined and the factor of safety (FOS) is computed. Attempts have been made in this work to address the stability of the riverbanks of the proposed sites and thereby help to adopt necessary measures to mitigate such failures.

Khagana Buragohain, P. K. Khaund

Analysis of Rainfall-Induced Shallow Slope Failure

Rainfall-induced shallow slope failure has proved to be disastrous in many parts of the world. Majority of slope failures pose a significant risk to infrastructure and public-safety largely due to rainfall-induced slope failures. The stability analysis of slope generally seeks to understand the cause of the slope failure. The penetrating water reduces matric suction within the soil thereby reducing the shear strength of the soil slopes. In this direction, this paper attempted to analyze the slope behavior under different rainfall intensities and at slope angles. A series of numerical analysis was conducted under a fully coupled flow deformation in PLAXIS finite element modeling code. The numerical trials to check the stability of slope were performed under two dissimilar states, (1) rainfall of certain intensity was applied to the slope for a period of 24 h, and (2) the slope stability was analyzed using soil nailing technique. Different rainfall intensities were applied to evaluate the maximum deformation and variation of pore-water pressure of the shallow slope. Results showed that with increasing rainfall duration, slope deformation increased thereby making the slope unstable. In addition, it is observed that the horizontal deformation in case of the reinforced slope gets reduced, hence increasing slope stability.

Tehseena Ali, Himanshu Rana, G. L. Sivakumar Babu

Slope Stability Analysis of an Earthen Dam Using GEOSTUDIO 2007 Software

Analysis of an earthen dam, especially its slopes, is very important these days as its failure may cause huge loss of lives and properties. These days numerical models are used to check the stability of an earthen dam. Numerical models simulate all the parameters, which affect the safety of an earthen dam. The most important parameters are properties of the soils used for the construction of an earthen dam. For the numerical modeling in this study, a finite element analysis software is used, i.e. GEOSTUDIO 2007 (SEEP/W and SLOPE/W). The parameters considered in this analysis are the site and its foundation conditions, soil material characteristics and hazard potential associated with the particular site. To find the factor of safety, a numerical model of SLOPE/W and SEEP/W program of GEOSTUDIO software is tested for steady-state condition and sudden drawdown. The Morgenstern-Price method, based on limit equilibrium, which is incorporated in SLOPE/W to analyse the model for four cases, namely earth dam without berm and without a toe drain, earth dam with berm without a toe drain, earth dam without berm with a toe drain and earth dam with berm with a toe drain. The results showed that out of four cases, the best case to improve the factor of safety of the slope is the fourth case, i.e. earth dam with berm with a toe drain.

Saurav Shekhar Kar, L. B. Roy

Static and Dynamic Analysis of Nailed Slope

In the present study, slope stability analysis is carried out for a nailed slope with 50° slope angle and 20 m height. Analysis is carried out by both 2D limit equilibrium and finite element methods using a geotechnical modeling software GeoStudio. Sections of slope without and with nails are analysed for stability with respect to static, pseudo-static and dynamic conditions. Dynamic response of nailed slope is analysed against an earthquake with PGA of 0.15 g by finite element method. The acceleration–time history is used as an input to simulate the earthquake in the numerical model. A parametric study is carried out to analyse the effect of nail inclination, nail spacing and nail length on the stability of nailed slope. The variation of factors of safety, shear stresses and displacements during earthquake is also analysed by finite element method using Geo-slope. From the analysis, it is found that the slope is unstable without nails with factor of safety 1.116 in static condition. And the factor of safety increases to about 1.628 by soil nailing. The slope with optimum nail inclination and spacing is analysed for dynamic response. The nailed slope is critical at 7th second of earthquake with factor of safety of 1.35 for an average acceleration 0.124 m/s2. Horizontal displacement of 60 mm is obtained at the top of the nailed slope due to earthquake. The displacements decrease from top to the bottom of the slope.

Chappidi Srinivas, M. Padmavathi

Design and Analysis of Earth Slopes Using Geosynthetics

In the aspect of geotechnical engineering problems, slope stability is a condition of inclined soil, waste heaps to withstand or undergo movement. Slope is an unprotected ground surface that can be necessitated at an angle of horizontal. Slopes are necessitated in the construction of railway embankments and highways, levees, bridges, earth dams, reservoirs and canals etc., and are generally less expensive. Failures of natural and man-made slopes have demise and demolition. Analysis and stability slopes consist of determining and comparing the shear stress developed along the potential rupture surface with the shear strength of the soil. The awareness of the surface drainage is very important factor. Slope stability can be evaluating the ground water, shear strength of the soil. For a secure slope, factor of safety should not be less than 1. In recent times, electronic computers made it feasible to more easily repetitious mechanism and the use of OASYS GE software has simplified the analysis to a great extent. In this present study, OASYS GE Slope software has been to analyze the homogeneous earth slopes for different cohesive strengths, and also we study the improvement of stability of slopes using geomembrane and we also consider the effect of ground water table on stability of slopes.

N. Vijay Kumar, S. S. Asadi, D. Satish Chandra, A. Shivamanth, G. Pradeep Kumar

Stability Analysis of Slope in Kuranjeri During Kerala Flood 2018 Using PLAXIS-3D

Landslide or landslip is defined as a type of mass movement in which a mass of rock, debris or earth down a slope under the direct influence of gravity. In this study, Kuranjeri of Thrissur district has been selected where landslides occurred during 2018 Kerala floods. In this case, landslide was triggered by incessant heavy rainfall followed by mass movement of debris. An investigation was carried out to discern index properties and soil parameters on the collected soil samples. Limit equilibrium method (LEM) is the most common approach for analysing slope stability by investigating the equilibrium of a soil mass tending to slide down under the influence of gravity. As a powerful alternative advanced numerical method, Finite element method (FEM) quantifies factor of safety against slope instability by strength reduction method of stability analysis using PLAXIS-3D. A comparison is then made between the results of LEM and FEM by in cooperating properties of in situ soil on slope failures. The analysis result unveils that the infiltration of water into the slope resulted in the failure of the slope on account of reduction of shear strength parameter of the soil.

Lakshmi Manohar, A. K. Vasudevan

Generalized Three-Dimensional Slope Stability Analysis of Soil Using Plaxis 3D

Slope stability analysis requires sound geotechnical knowledge as well as sophisticated computer code for the design. The set of simplified design charts for analyzing the stability of soil slopes is developed by conducting a number of three-dimensional slope stability analysis using finite element code Plaxis 3D. Three-dimensional slope stability analysis was done for homogeneous clay under varying cohesion in different slope height. Also, the variations factors of safety for dry and partially saturated condition were compared. It is observed that the factor of safety increases when cohesion increases and decreases with increase in slope height.

P. M. Shafna, T. R. Anjana

Stability Assessment of a Soil Slope in Meghalaya, North-Eastern India

Landslides are a common occurrence in hill slopes in the seismically active north eastern part of India. The soil slopes are highly vulnerable to failure due to heavy earth cuttings, rainfall and blasting activities during road construction. When landslides occur in transportation corridors running along hill slopes, there is the risk of huge loss to lives and property. In addition, the communication through these networks could be brought to a standstill during such catastrophes, resulting in considerable amount of time and resources expended in restoration of traffic and causing huge inconvenience to commuters. In this scenario, the need arises for a proper investigation on failure mechanisms of hill cut soil slopes and to envisage on appropriate mitigation measures. In the present study, stability analysis is carried out of in situ soil slopes newly exposed during a road widening along National Highway-40, a strategic road corridor in Meghalaya. The analysis consists of a limit equilibrium approach wherein the slope has been modelled using in situ soil conditions. The factors of safety of the slope against sliding failure have been calculated and the critical slip surface has been found by limit equilibrium analysis. The results of numerical modelling using the commercially available software SLOPE/W indicate unstable slopes potentially vulnerable to failure under adverse conditions. Necessary mitigation measures that need to be taken have been suggested based on the vulnerability condition of the slope.

Antareep Kumar Sarma, Ashesh Choudhury, Koustavjit Sarma, Anangsha Alammyan

Assessment of an Open Cast Coal Mine Slope Stability at Mohanpur Block, Raniganj Coalfield, West Bengal, India

A large open cast coal mine always needs a stable side slope to prevent collapse due to excessive overburden pressure. The present study was undertaken to assess the stability of slope of an open cast coal mine located in Mohanpur block in the Raniganj coalfield area in West Bengal, India. The pseudo-static approach of stability analysis was performed using Plaxis 3D software package under strength reduction technique. A Mohr–Coulomb constitutive model was considered for the simulation of geological materials under drained and undrained conditions. The average overall depth of the mine slope was considered as 144 m. The slope was designed following the coal mine regulations of mechanized open cast mining (CMR 2017) [1], Ministry of Labor and Employment, Govt. of India. The maximum vertical deformation and safety factor were examined to ascertain the optimized slope angle of the Mohanpur open cast pit. Three trial slopes were considered using three different slope angles. The slope angle of 40° was selected as the design slope as the safety factor as well as vertical deformation was found to satisfy the permissible limits under seismic accelearations considered in the present study.

Agami Pramanik, Avishek Adhikary, Supriya Pal

A Numerical Study on Geotextile-Reinforced Slopes

In recent times, use of geosynthetics has gained widespread acceptance and has been used as reinforcing component in numerous geotechnical engineering structures. During construction of geotextile-reinforced slope, it become essential to maintain certain value of factor of safety for each stages of construction. In this paper, a numerical study on slopes reinforced with and without geotextiles is presented. To capture the trend of development of axial forces in the geotextile layers under plastic analysis, four different slope inclinations (β) (i.e., β = 45°, 60°, 75° and 90°) with slope height of 7 m were selected. Reinforced slopes were provided with equal number of geotextile layers along with uniform length (Lg) of 6.4 m. The uniform vertical spacing (Sv) of 1.0 m between any two geotextile layers was chosen. To simulate staged construction method which is adopted at site, finite element tool PLAXIS 2D was used for stability analysis. The construction of slopes was simulated in seven stages of equal height for all the slope inclinations. The results showed that minimum axial forces were developed at the top most geotextile layer for all the four slope inclinations (β = 45°, 60°, 75°, and 90°). Maximum axial forces were observed to develop in all geotextile layers for the slope having β = 90° when it compared to other slope inclinations. With an increase in axial stiffness (EA) of geotextile layers by 100%, it was noticed that only 16% increase in axial force at the bottommost geotextile layer for the slope with 75° inclination.

Hardik V. Gajjar, Veerabhadra M. Rotte
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