Geotechnical Characterisation and Geoenvironmental Engineering

Soil compaction is a vital part of the construction process. The compaction curve between moisture content and dry unit weight should be prepared for all types of soil in the project area, before earthwork commences as it forms the basis for specification and field compaction control. The relationship between moisture content and dry unit weight of the soil is a function of the compactive effort. The modified Proctor test, the reduced modified Proctor test, the standard Proctor test and the reduced standard Proctor test are dynamic methods which use different compactive efforts. These tests require considerable time and effort, and also these have some imperfections. In the present study, a laboratory procedure is devised to determine the relationships between moisture content and dry unit weight by using static compaction method for different static pressures. The static compaction pressure test is devised in the Proctor mould itself to statically compact the soil at different water contents. This method is less laborious, and the time involved is less. For this, seven fine-grained soil samples of various plasticity characteristics were tested. The analysis shows that the relation between water content and dry unit weight in static compaction for different static pressure is parabolic in nature. In this study, the equivalent static pressures to the modified Proctor test, the reduced modified Proctor test, the standard Proctor test and the reduced standard Proctor test are determined, to obtain the maximum dry unit weight and the optimum water content corresponding to the four different compactive efforts.

Many hydroelectric, metro rail and nuclear repository projects are under construction in the country. The structures for these projects, which include dams, tunnels, powerhouse caverns, are mostly constructed on/in rocks. The characterization of the behaviour of rock forms essential part of the analysis and design of these structures. Many of the rocks around tunnels and underground caverns exhibit strain softening behaviour under loading. Strain softening is defined as the progressive loss of strength when material is compressed beyond peak. The present paper deals with the testing of an igneous rock, i.e. basalt from hydroelectric project located in Madhya Pradesh in India. The testing has been conducted using closed-loop servo-controlled testing machine under strain-controlled loading. The specimens were prepared as per ISRM standards. The diameter of the specimen was 54 mm, and the length of the specimen was 108 mm. The index properties of the rock were determined as per ISRM standards. Triaxial tests were conducted under various confining pressures at a constant axial strain rate of 9.259 × 10−6 s. The strains were measured with the help of strain gauges and specially designed extensometers. The stress–strain–volume change relationships of the tests are presented and discussed in this paper. The behaviour of basalt is also predicted using an elastoplastic constitutive model, i.e. Mohr-Coulomb strain softening model using FLAC. The material parameters for the model are determined from the experimental results. The stress–strain–volume change response of the basalt is then predicted using the material parameters and is compared with the observed results. The predictions using the constitutive modes are found satisfactory and comparable with the experimentally observed results.

Large amount of industrial wastes are generated from various factories in India and are simply being disposed without any major applications. Alternative materials are to be adopted as a construction material so as to minimize the use of natural resources. Red mud (RM) is generated as a waste material during the production of alumina from bauxite, and it comes to around 40% of the bauxite used for the production. The paper presents the possibility of using red mud as a stabilizing material. The study examines the effect of red mud on behavior of clays by carrying out compaction test, CBR tests, and UCC tests for different percentages of red mud. The red mud soil mix is further treated with lime to understand whether more soil can be replaced by red mud on lime treatment. It was seen that the highest maximum dry density (MDD), UCS, and CBR values were obtained for 15% red mud in soil. On further treatment with 2% of lime, 20% red mud in soil showed more strength compared to 15% red mud in soil ensuring that more soil can be replaced by red mud on treating with lime.

Natural well-graded granular materials are conventionally used as a fill material for various geotechnical applications. However, due to high demand for granular material, illegal dredging of sands from the river beds is on the rise. On the other hand, a study carried out by Centre for Science and Technology, New Delhi, has reported that huge amounts to the tune of 530 million tonnes of Construction and Demolished (C&D) Waste were generated during the year 2013 in India. This C&D waste includes waste from demolished structures due to renovations of existing structures and repair of roads, flyovers, bridges, etc. In addition, enormous debris is generated following disasters such as that during the Uttarakhand floods in 2013. Typically, C&D waste is dumped in municipal landfills. This study presents the efficacy of crushed concrete and concrete rubble for use as an alternate backfill material in mechanically stabilized earth (MSE) walls. Crushed concrete (CC) is collected locally from the demolished structures of Ordinance Factory Campus, Yeddumailaram, Telangana, and processed before testing. Various index and engineering properties of CC such as particle-size distribution, specific gravity, water absorption, permeability, compaction characteristics, and crushability are ascertained and compared with TxDOT and MORTH specifications for fill materials. Corrosion resistivity of CC is determined by pH test, and the chemical composition of CC is obtained from X-ray fluorescence (XRF) studies. CC is classified as well-graded gravel (GW) as per IS: 2720 (Part 4)-1985. The study indicates that C&D waste, traditionally considered as waste material, can be reused viably as backfill for MSE walls.

Quality assessment and control (QA/QC) of compacted pavement layers involve regular monitoring of density and moisture content during compaction. In situ density is traditionally determined using sand-cone test method. However, many recent studies have indicated that stiffness- or strength-based quality measurements are easy to determine and more reliable than the density-based quality measurements. In this study, lightweight deflectometer (LWD) is used as a quality control device to assess the quality of compacted pavement layers. As a part of this study, an extensive LWD field testing program is undertaken on the expressway along the Outer Ring Road (ORR) located in Hyderabad, India, to determine the modulus of deformation (ELWD) of base and surface pavement layers. ELWD of compacted base and surface layers was found to commonly range from 37.6 to 58.6 and 89.3 to 125.7 MPa, respectively. In addition, a case study on a low-volume road is presented to demonstrate the relationship between the ELWD and in situ density obtained from the sand-cone test. LWD is found to be simple to operate and provides quick test results on any pavement layer. Hence, the frequency of quality control tests can be increased leading to an improvement in the overall quality of compacted pavement layers.

In geotechnical engineering field, bentonite–sand mixtures have been proposed and used as engineered barriers for containing the waste. This paper presents the laboratory evaluation of compressibility by performing one-dimensional consolidation tests on six different mixtures of bentonite with sand. The bentonite–sand mixtures were formed by varying sand content in bentonite in increments of 5% from 5 to 25% by dry weight. Dry bentonite–sand mixtures were placed initially in the consolidation cell at their loosest dry state and then allowed to saturate. Swelling characteristics and swelling pressures of the bentonite–sand mixtures were also evaluated. This paper also presents the laboratory evaluation of permeability of the bentonite–sand mixtures by performing falling head test after every load increment during the consolidation test. This study arrived at the conclusion that amount of swelling (expressed in percentage) and swelling pressure decreased with addition of sand. Moreover, changes were observed for the consolidation parameters upon addition of sand to bentonite. The void ratio versus log of permeability plots was found to be linear, and permeability was found to increase with increase in sand content.

Natural sands are rarely found as clean sands. They contain considerable amounts of plastic (clay) or non-plastic (silt) fines. If fines are present in sufficient quantity to separate the sand particles, soil behavior will be significantly controlled by the fines. The fabric of such a soil is referred to as floating fabric. Characterization of sand with the presence of fines is important in the design of geotechnical structures. This paper presents a detailed study focused on investigating the effect of plastic fines on the engineering properties of sand–fines mixture. Mixtures of sand and fines are prepared by mixing clean sand with plastic fines (clay). Indian Standard (IS) Grade II sand, widely known under the name of Ennore sand, is used during experimentation. This sand used is classified as poorly graded (SP) as per Unified Soil Classification System (USCS). Plastic fines are obtained locally, and the liquid limit (LL) and the plasticity index (PI) are found to be equal to 65 and 39%, respectively. The effect of plastic fines on shear strength of sands is studied using direct shear testing conducted in displacement-controlled mode. Tests are performed at 0.5 mm/min, and the samples are subjected to three normal stresses—50, 100, and 150 kPa. In addition to determining the shear strength, this study also focused on volumetric changes of specimens during shearing in a direct shear box. Tests are conducted on specimens of sand with various fines content ranging from 0 to 25%, while maintaining a constant total density of 1.7 g/cc throughout. Plots of shear stress versus horizontal displacement of lower box, and vertical displacement versus horizontal displacement are reported. The shear strength envelopes of sand specimens prepared at various percentages of fines are proposed. The test results showed that both friction angle and apparent cohesion decrease with increase in fines content in sand–fines mixture, thereby shifting the shear envelope downwards. In addition, there is a consistent decrease in peak shear strength with increase in fines content.

The quality and acceptability of a waveform data collected during spectral analysis of surface waves (SASW) testing is judged based on the coherence function over the measured range of frequencies. However, many trials and repetitions are required during SASW testing to obtain data with acceptable coherence value (>0.95). This makes the test time-consuming, and in most cases, only small portion of the collected data that satisfies the acceptable coherence criteria can be used for analysis. In this research study, an attempt was made to study the effect of using an impact source of constant energy on the coherence function as compared to the use of traditional handheld hammers. Laboratory experimental studies were performed on sandy clay soil bed filled in a metal box of dimensions 1.5 m × 0.61 m × 0.45 m. Also, a series of field tests were performed to validate the applicability of the laboratory findings. In both laboratory and field testing, a 2.5 kg hammer was used with height of fall as variable parameter. Two sets of tests were performed. One with random height of fall that is similar to current practice and the other with fixed height of fall of 0.13 m to simulate impacts with same energy conditions. Test results depicted that unlike the conventional procedure of testing, the use of constant energy of impact leads to coherence close to 1 over a significantly large frequency bandwidth. This research highlights the effect of using constant and varying impact energy on coherence value over a wide range of frequencies obtained during SASW testing.

The coastline of India is speckled with a large number of ports (major and minor). In connection with the construction of new ports and upgradation of existing ports, a lot of construction has taken place over a decade or two. This involved jetties, container yard, railway connectivity to existing railway network, deepening of berth pockets and channels, etc. On the geotechnical front, these involved reclamation, embankment construction, pile foundations, deep excavations, etc. The east coast of India is characterised by silty clay over a large distance from West Bengal to Tamil Nadu cutting across Odisha and Andhra Pradesh. A few kilometres inland from the coast, the region also comprises silty clay, probably residual deposits arising out of weathering of volcanic rocks. In this paper, laboratory test data from many of the sites are analysed to look for any behavioural pattern. The compression properties of the cohesive soils are looked into and compared with correlations available in the literature. It is seen that the compression characteristics do follow a definite trend although there is scatter. The aim of publishing this field data is to help designers in selecting parameters in the preliminary design stage before any detailed investigations are carried out. This could also help in estimating quantities for tender preparations with a fair amount of certainty on the primary consolidation settlements resulting from reclamation, embankment construction, and also the extent of ground improvement required, if any.

The unconfined compressive strength is one of the influencing parameters that are used for determining the in situ strength of soft, fine-grained soil deposits. Since many previous research works have highlighted the influence of pore fluid type, electrolyte concentration, pH and valence of the pore fluid on unconfined compressive shear strength. The present study has inferred the effect of pore size distribution (PSD) on unconfined compressive shear strength (UCS) of bentonite and kaolinite minerals. It is observed that the pore size distribution of bentonite is a bimodal distribution representing both interpore and intrapore, whereas the kaolinite mineral exhibits a unimodal distribution representing only the interpore. The interpore represents the water molecules bounded between soil aggregates, whereas the intrapore represents the water molecules bounded within the soil aggregated and on the clay surface. From the obtained UCS value of bentonite and kaolinite minerals, it can be inferred that the UCS strength variation of bentonite mineral is strongly influenced by the water molecules bounded on the clay surface or diffused double layer water, whereas the UCS strength of kaolinite minerals is controlled by the net attractive force between the clay particles. The present study demonstrated that the pore size distribution is also one of the parameters that strongly influences the unconfined compressive strength of the soil.

Fly ash and blast-furnace slag are well-known industrial by-products and are used to manufacture blended cements and concrete. Fly ash has been used as pozzolanic material to improve the physical, mechanical as well as chemical properties of the cements and concrete, whereas blast-furnace slag cements are characterized by their low heat of hydration and high sulphate and sea water resistance. On the other hand, addition of blast-furnace slag to fly ash may have substantial influence on the strength development of geopolymer binder when cured under ambient temperature condition. This paper presents the compressive strength of geopolymer binders synthesized from Class-F fly ash (FA) blended with ground granulated blast-furnace slag (GGBS) by optimizing the influential parameters. The chemical activation of fly ash–slag mixtures with different concentrations of sodium hydroxide (NaOH) for varying solution to solid ratio has been made. The test results showed that the development of compressive strength is directly concomitant to concentration of NaOH solution. Moreover, as the slag content in the mixture increases, the compressive strength increases. Hence, an inorganic polymer can be synthesized from fly ash–slag mixture by activating with appropriate amount of NaOH which can be used as cementitious material.

Conventional triaxial tests mostly use external LVDTs attached to the actuator of automated triaxial system so as to measure the strain. However, these LVDTs measure the external strain applied and not the strain developed in the sample during shearing. This paper presents the use of on-sample transducer to measure localized strain in a soil sampled subjected to triaxial tests. Specimens prepared at two relative densities (30 and 90%) and three effective confining pressures (50, 100 and 150 kPa) were tested with displacement rates of 0.005 and 1.2 mm/min. It has been observed that the slower rate of loading poses significantly higher secant stiffness of soil. The use of on-sample transducers provides a wide range of strains, i.e., from low strain (~ 1 × 10−3%) to high strain (>1%), and can be used to evaluate the modulus reduction curve over the investigated wide range of strain. The capability of on-sample transducers can be effectively harnessed to evaluate the maximum shear modulus of a soil.

Hillslopes within the city of Guwahati consist of geological stratification that characterize progressive stages of residual weathering, which can be categorized as basal rock, decomposed granitic rock and corestones, saprolitic and lateritic residual overburden. Saprolite formation is the layer of residual soil derived from isovolumetric weathering of the bedrock. Undisturbed saprolite formation looks very compact and retains much of the parent rock structure and fabric, but actually is extremely porous due to washing out of the finer particles. Such soils are very friable and once disturbed are exceedingly susceptible to landslides. Several rainfall-induced landslide occurrences have been reported in the hillslopes of Guwahati region. Characterization of these soils is important for proper analysis of hillslope stability of this region. Laboratory test has been performed on disturbed and undisturbed soil samples to assess the geotechnical characteristics. Test to determine grain size distribution, specific gravity, Atterberg’s limits, in situ dry density, shear strength parameters, and permeability were conducted. Hillslopes within Guwahati region consist of residual soils in unsaturated condition. The soil–water characteristic curve, which is an important characteristic of unsaturated soil, is determined and compared with that obtained from empirical methods using grain size distribution and Atterberg’s limits provided in the literature. Unconsolidated undrained triaxial test was conducted on statically compacted samples remoulded to in situ density at different water content to understand the effect of degree of saturation and moisture content on the shear strength of the soil. Such detailed characterization would provide the requisite understanding for an efficient analysis of the rainfall-induced natural hillslope failure in this region.

In this paper, an attempt is made to analyse the dilative behaviour of dense sand at two different sizes of the direct shear box, i.e., small (60 mm × 60 mm × 30 mm) and large (305 mm × 305 mm × 140 mm). A three-dimensional numerical model is developed using the FLAC3D software to analyse the size effect on dilative behaviour of dense sand along the top and the shear plane of the box at 15 kPa normal pressure. It is observed that the vertical deformation of soil on top plane increases linearly with horizontal displacement, whereas on shear plane, the vertical deformation remains constant after yielding of sand. It is also found that there is greater movement of sand particles at the front and the back of the box for the large shear box compared with that for the small shear box.

Soft soils are found along east and west coast of Kerala. They exhibit unusual engineering properties like high natural water content, high compressibility, low permeability and low shear strength. Availability of land for the development of commercial, housing, industrial and transportation, infrastructure, etc., is getting scarce nowadays. This necessitated the use of land, which has weak strata, wherein the geotechnical engineers are challenged by the presence of different problematic soils with varied engineering characteristics. Not much work has been done to understand the behaviour of these soils. Hence, it is necessary to study the geotechnical behaviour of such soils including the effect of various parameters. As far as Kerala is considered, soft clays are predominant in Kuttanad and greater parts of Cochin. Research works carried on Kuttanad clay and Cochin marine clay mainly focused on compaction, compressibility and UCC strength. Clayey soils are impervious and do not permit drainage of water. There will be a cumulative build-up of pore water leading to increase in pore water pressure and reduction in shear strength, finally leading to increase in settlement and deformation. Not much works have been done on laboratory modelling of the soft clays of Kerala and its behaviour under the influence of varying parameters. Soil properties vary from point to point due to the variations of field parameters. The objective of this paper is to investigate the effect of various parameters influencing undrained behaviour of Kuttanad clay. Confining stress and density were studied. For this purpose, consolidated undrained triaxial test was performed with pore pressure measurements. Typical deviator stress–strain graphs, pore pressure versus strain graphs, and stress paths were drawn for all the tests conducted.

Water vapour diffusion is a predominant moisture transport mechanism in an unsaturated soil due to the presence of either thermal gradient or concentration gradient. In such soils, as water content decreases, the continuity of liquid films is lost, and as a result, water movement is mainly in the form of water vapour. The knowledge of water vapour migration characteristics of geomaterials is important in the performance evaluation of underground buried services, compacted/geosynthetic clay liners, geothermal energy utilization, thermally enhanced clean-up of contaminated sites and the containment facilities for disposal of high-level nuclear waste. In view of this, the present study describes a methodology to investigate the water vapour diffusion through geomaterials under isothermal conditions. Further, the study evaluates the effect of particle size and compaction state on water vapour diffusion characteristics of the soils.

Sand-bentonite mixtures are assuming greater importance as geotechnical barrier materials in waste disposal schemes around the world, and like with any other geotechnical soil structure, a comprehensive understanding on the engineering behavior of various components used in the making of a geotechnical barrier becomes a necessity. A review of the literature indicated a host of variables influencing the engineering behavior of a barrier to various degrees, including and not limited to mineralogy of the soil, size, and shape of particles, their interactions among themselves, interactions with water, interactions with any other pore fluid that may exist in the soil, pH, temperature, cation exchange capacity, and quantity of cations in the soil pore fluid. Upon scrutiny, it has been observed that most of the studies conducted were primarily focusing on the role of bentonite in the sand-bentonite mixture, and studies highlighting the contributions of sand particle size, sand gradation, etc., were very few even though sand forms the major component in most of the sand-bentonite mixtures being employed around the world. This study sheds some light on the plasticity characteristics of sand-bentonite mixtures with varying bentonite proportions and sand compositions. In the current study, locally available sand has been washed thoroughly and sieved for different particle sizes (fine sand and medium sand) and two commercially available bentonites were procured. Fine sand-bentonite (FS-B), medium sand-bentonite (MS-B), and fine sand-medium sand-bentonite (FS-MS-B) mixtures were made with bentonite proportion varying from 10 to 50% by dry weight in the mix and were tested for Atterberg limits. Liquid limit results indicated that, for a given bentonite content, FS-B, MS-B, and FS-MS-B mixes exhibited different liquid limits and sand composition has a little influence on the liquid limits. Shrinkage limit results indicated that sand composition has a notable influence on the shrinkage characteristics of the sand-bentonite mixtures.

Permeability of gases through geomaterials are critical in areas like landfill cover design, buffer material characterization in deep geological repositories for radioactive waste containment, geosequestration of greenhouse gases, oil and gas recovery. In general, there are two types of laboratory methods for determination of gas permeability of geomaterials, such as steady-state and transient or pressure decay methods. In all these methods, the sample thickness that needs to be considered is important for accurate estimation of gas permeability characteristics. In view of this, the present study discusses the effect of sample thickness on the laboratory determination of gas permeation through geomaterials. A permeability apparatus has been developed for evaluating the gas permeability characteristics of geomaterials over a range of compaction state, based on the concept of pressure decay. Further, the experiments are conducted at different sample thicknesses along the standard Proctor compaction curve and the effect of sample thickness on gas permeability has been evaluated.

Rapid industrialization and urbanization cause release of significant quantities of hazardous contaminants, including heavy metals and radionuclides, into the biosphere. Severe accumulation of these contaminants and their exposure deteriorates human health, environment, and biota system. Conventional remediation of heavy metal, radionuclide contaminated soils includes physicochemical extraction, stabilization/solidification/immobilization, soil washing. These techniques demand large quantities of chemical reagents, huge cost apart from the generation of secondary toxic by-products, and hence, the aforementioned techniques become unsuccessful and ineffective. This necessitates an interdisciplinary approach using biomediated processes and/or derived by-products, which enhances remediation process through accelerated biogeochemical phenomenon. Bioremediation is a broad area which involves large matrix of remediation techniques such as bioaccumulation, biosorption, biosparging, bioleaching, biomineralization, phytoremediation. Among all these techniques, biomineralization or microbially induced carbonate mineral precipitation is the most fascinating, promising methods to handle the present-day challenges pertaining to remediation of contaminated soils. In view of this, the current study presents a critical review on mechanisms of microbially induced carbonate precipitation in view of solid-phase sequestration of inorganic contaminants. Further, this study assesses the suitability of various microorganisms along with the associated precipitation processes for transforming soluble inorganic compounds into stable and non-redox sensitive carbonate minerals.

The benefit from using admixtures in soil to improve properties was discovered in ancient times. Various admixtures such as straw, bitumen, lime, salts and pozzolans are conventional additions to soil, while cement, petrochemicals and bacteria are currently being increasingly used in an effort to improve and stabilize soil from both mechanical and chemical aspects. The conventional techniques which utilize cement, lime, petrochemicals, etc., cause significant environmental degradation. With environmental awareness for materials and methods used in ground improvement generally growing, the trend towards using biopolymers as admixtures is expected to increase. This paper gives the concept and theory of ground improvement technique which employs biopolymers and describes the practical application of these techniques. A number of studies have been conducted in the past decades to check the suitability of various biopolymers in improving soil properties. The effectiveness of biopolymers for soil stabilization in agricultural, construction and military applications has been recognized by many researchers. More efficient and scientific usage of these materials for soil improvement requires knowledge about interaction mechanisms involved in the modification of geotechnical properties of soil. Most of the studies in clay–polymer interaction are from the field of medical engineering, where clay particles are suspended in the colloidal form and macromolecules are attached to them in different ways. The fundamental mechanism in biopolymer–soil modification proposed by various researchers is also presented in this paper. The study reveals the prospects of this green technology in the current era of rapid deterioration of natural resources. Furthermore, the need for continuing research on a number of factors which controls the mechanism is suggested.

Electro-kinetic properties of colloidal substance can be studied in terms of its zeta potential, which indicates the stability of the colloidal system. Numerous investigations have been made in the past several decades in areas of electro-kinetic remediation and stabilization of fine-grained soils. A proper understanding of the underlying mechanism of the above processes demands a thorough knowledge of the zeta potential of the system. Further, the electro-kinetic process can significantly alter the physio-chemical and electrical properties of the clay-water-electrolyte system which is also manifested as a change in the zeta potential value. Various environmental factors that affect the zeta potential include temperature, electrolytic concentration, cation valency and pH of the medium. The investigations made in view of understanding the role of zeta potential in determining electro-kinetic efficiency of various soils are widely scattered and no attempts have been made so far to interpret the available data, making it difficult to arrive at any conclusive inference. In this context, the present study attempts to evaluate the investigations carried out, by the previous researchers, to identify the factors that are influencing zeta potential and its role on electro-kinetic properties of clay minerals. In addition, zeta potential measurements are conducted on kaolinitic type and Na-bentonite soils over a wide range of pH and the results are compared with the data available in the literature.

The estimation of the model parameters namely effective diffusion coefficient and retardation factor of a potential landfill liner material was presented in this paper using the experimentally measured salt concentration data. Experimental data of concentration variation of time and spatial distance in compacted bentonite was obtained using two diffusion measurement techniques viz. through-diffusion and half cell technique, respectively. The bentonite was subjected to the same concentration gradient and compacted density in both the experimental methods to compare the results and understand underlying mechanism in the diffusion tests. The measured data from the laboratory diffusion techniques was analysed using a Graphical User Interface (GUI)-based Dot-net application CONTRADIS. The CONTRADIS was used to estimate the model parameters by the inverse analysis. The application uses the solution of the forward analysis and stochastic algorithm for the inverse analysis. The retardation factor obtained theoretically was validated using laboratory batch sorption tests.

Improper dumping practices may consume more land and contaminate the surrounding environment. There is a necessity to design a proper sanitary landfill in order to control the environmental effects. If a locally available soil meets the criteria of landfill material, the locally available material can be used to construct the compacted clay liner (CCL). This paper presents the feasibility study on the utilization of the locally available red earth as a landfill liner based on its contaminant sorption capacity. The potential for retention of lead (Pb2+) by red earth from the Warangal city in India is examined. Lead solution of varying initial concentrations and pH values were used for the analysis. In addition, an attempt is made to observe the influence of organic chemical (EDTA) on the retention capacity of red earth. Batch sorption tests were conducted for a single salt solution with and without organic chemical, and results were presented. From this study, it is revealed that with an increase in the initial concentration of the lead solution from 10 to 30 mg/L, the percentage removal was decreasing. Whereas with an increase in pH from 2 to 7, the maximum increase in percentage removal was observed as 23% at maximum initial concentration (30 mg/L). With the presence of organic chemical, at neutral pH value, the decrease in the sorption capacity of soil was at least 36% at maximum initial concentration (30 mg/L).

Compacted expansive soils are widely used as engineered barriers in waste contaminant applications like landfills, brine ponds, and nuclear waste disposal sites. These liners are designed for very low hydraulic conductivity (<1 × 10−7 cm/s). Percolation of chemical waste or leachate results in physicochemical changes in compacted expansive soils which increases the hydraulic conductivity. This paper brings out the changes in swelling behavior and hydraulic conductivity of compacted expansive soil induced with osmotic gradients using NaCl and CaCl2 solutions. Multiple identical soil specimens placed in oedometer assemblies were inundated with distilled water, 0.4 and 4 M NaCl (monovalent cations), and 0.4 and 4 M CaCl2 (divalent cations) salt solutions and allowed to swell under a surcharge pressure of 12.5 kPa. Void ratio–water content plots were also traced during swelling process. Falling head permeability tests were conducted on swollen soil specimens in rigid wall oedometer permeameters under a hydraulic gradient (i) of 20. The experimental results showed that the swell potentials reduced and hydraulic conductivity increased with the increase in induced osmotic suction.

The liners play an important role in controlling migration of contaminant present in the leachate in waste containment system such as landfills. Compacted clay liners are widely used because of their low permeability and large attenuation capacity. Nowadays the lack of availability of natural clay with satisfactory engineering properties resulted to look for an alternative material for liner. Commercial clay such as bentonite is commonly used for liner material. Fly ash is an industrial waste produced from thermal power plant, and disposal of this material is a serious problem. The present study is carried out to evaluate the capability of laterite-fly ash-bentonite liner to attenuate contaminant in municipal solid waste leachate. Laterite soil for the present study is collected from NIT Calicut campus. A series of laboratory tests were conducted to investigate the combined effect of fly ash and bentonite added at different percentage of lateritic soil as landfill liner. Suitable laterite-fly ash-bentonite mixes satisfying liner criteria were identified, and batch adsorption tests are performed on this mixes with hexavalent chromium as model contaminant. 78% removal efficiency was achieved for laterite soil mixed with 30% fly ash and 5% bentonite.

An engineered landfill necessitates an impervious barrier to control the intrusion of groundwater into the landfill facilities and migration of leachate to the surrounding ground. The liner material should have sufficient shear strength along with highly impermeable. This paper aims at investigating certain features of a novel material that may serve as a landfill liner material as a substitute to sand-bentonite mixture. In this investigation, bentonite was blended with coarse pond ash ranging from 0 to 30% by weight of the total material in 5% intervals. The compaction characteristics, strength behavior, and permeability characteristics of these mixes are evaluated. It is observed that with bentonite content varied from 20 to 30%, the average hydraulic conductivity reduces from 3 × 10−7 to 9 × 10−9 cm/s for samples compacted to MDD at OMC corresponding to a compactive effort of 595 kJ/m3. However, when the samples are compacted with 2674 kJ/m3 energy; the hydraulic conductivity as mentioned above is achieved at a bentonite content of 15%. With the gradual addition of bentonite the cohesion of the mixture increases whereas the angle of internal friction decreases. Hence, it is concluded that sand-bentonite mixes can effectively be replaced by pond ash-bentonite mixture in the landfill liners.

Currently, nearly 170 million tonnes of coal ash is generated annually in India from 85 thermal power plants, and because of the limited availability of land, vertical expansions of ash dykes are unavoidable. The present paper compares the variability in engineering behaviour of coal ash from two different thermal power plants (TPP) A and B and highlights the influence of the variability in coarse particle content on design of ash dykes. Using the geotechnical properties of compacted ash as well as hydraulically deposited ash, ash dyke sections have been designed and a series of stability runs are carried out to map the factor of safety at various stages of ash dyke raising. The results indicate that slopes of ash dykes have to be made flatter as bottom ash content decreases in pond ash due to increased utilization or separate storage of bottom ash.

Virus present in the groundwater is considered to be an important agent for waterborne diseases in India. In order to predict how far viruses can be transported and how long they can remain infective in soil and groundwater is desirable for proper management of the placement of sources of contamination so that they will not have an impact on drinking-water wells. With respect to that, a one-dimensional virus fate and transport model is developed for transient heterogeneous unsaturated flow to identify the transport parameters in the unsaturated zone. Simulation of virus transport in groundwater aquifer is necessary for predicting the vertical movement of virus in an aquifer and to implement remedial measures to inactive the virus present in the groundwater. The model involves solution of the advection–dispersion equation, which additionally considers virus inactivation rate in the solution. In case of unsaturated porous media, the transport of virus is responsible for some of the parameters such as linear distribution coefficient, hydrodynamic dispersion coefficient and inactivation coefficient for both aqueous and sorbed virus. As there are often changes in the state and content of soil water during flow, it is considered to be a highly nonlinear problem and for such it becomes necessary to solve the flow equation before solving the virus transport equation. In this study, finite element scheme computer-coded software, HYDRUS-1D is used to simulate the one-dimensional flow equation and virus transport equation. This study is mainly carried out for a particular location of Guwahati City, Assam, India. The viruses that is been employed in this study were the male-specific RNA coliphage MS2, and the Salmonella typhimurium phage, PRD1. For simulating the partial differential equation of virus transport equilibrium, solute transport model is selected with Crank–Nicholson as time weight scheme and Galerkin finite elements as space weight scheme. The purpose of this research is to determine the role that unsaturated flow conditions play in virus sorption and inactivation during transport through different soil type. The effects of the moisture content variation on virus transport in unsaturated porous media were also investigated. The results obtained after several simulations indicate that the concentration of virus is affected by the moisture content and the heterogeneity of the soil profile during its flow through unsaturated zone. The model developed in this study can successfully simulate the virus transport through heterogeneous unsaturated columns.

Bentonite was added to a locally available rock dust to study the behaviour thresholds of the binary mix. Thresholds may be defined as the critical fines content above which the system behaviour changes drastically. By understanding the threshold values of such binary mixtures will help us to have a better control over its behaviour. In this study, the hydraulic conductivity and the swelling behaviour of quarry dust mixed with increasing fractions of bentonite were studied. Index properties of quarry dust were determined by standard sieve analysis, mini-compaction and by cone penetration method. The specific gravity of the quarry dust was about 2.65. The addition of bentonite to quarry dust has found to increase the maximum dry density and reduce the hydraulic conductivity by several orders. The swell potential of the various mix proportions was studied in an oedometer. Samples were of 14 mm thickness and were given a hydration period of 24 h and were compacted at their OMC and MDD. Mixes with low bentonite contents such as a 5% and 10% showed no swelling. The substantial swelling was only observed with 15% bentonite and more.

Most of the industrial effluents are disposed into land containing a variety of combination of chemicals that may bring in considerable changes in the geotechnical properties of soils. The tannery effluent is one such effluent characterized by high BOD and COD, high dissolved solids, high or low pH, presence of heavy metals, calcium salts, chlorides, sulphides, fat, liquor and organic dyes. This paper presents the laboratory results to study the effect of tannery effluent on the index and engineering properties of cohesive soil upon contamination. A series of laboratory tests have been carried out to evaluate the index and engineering properties of tannery contaminated clay soils. The virgin characteristic of clay soils is highly swelling clay of CH classification with differential free swell of 66%. Virgin clay soils have artificially contaminated with varying percentage of tannery effluent collected from Pallavaram in Chennai and tested to evaluate various properties of soils. The results had shown an increase in Atterberg’s limits as well as the shear strength with varying percentage of tannery effluent. The nature of the pore fluid has also found to significantly affect the index properties and shear strength.

In the present scenario, due to the urbanization and industrialization, much of the air, water and land have become polluted. Any kind of pollution has direct or indirect effect on the properties of soil. So in the present study, the effect of pH on the properties of two soils was studied. In the present study, effect of pH on the Atterberg limits of two soils was investigated using different pore fluids at different pH. Different pore fluids such as NaCl, KCl, NaOH, and KOH at different pH were selected such that pH varying from 6.5 to 13 could be obtained. From the present study, it could be seen that for the same solution with increase in pH the liquid limit was found to increase with decrease in pH both in the case of kaolinite and bentonite. Plastic limit is of lesser importance with regard to pH, both in the case of kaolinite and bentonite. The effect of pH on shrinkage limit in the case of kaolinite and bentonite showed extremely opposite behavior.

The influence of geomembrane in maintaining the sealing efficiency of a landfill cover system at the onset of flexural distress was studied by conducting a series of centrifuge tests performed at 40 gravities. The tests were performed using a 4.5 m radius beam centrifuge having a capacity of 2,500 g-kN available at IIT Bombay on model composite barriers of 0.6 m thickness. The thickness and tensile stiffness of the geomembrane were varied. All the models were instrumented with pore pressure transducers (PPTs), linear variable differential transformers (LVDTs), a digital camera and a charge-coupled device (CCD) video camera to study the performance of the barriers during centrifuge tests. The sealing efficiency of the composite barriers was found to be maintained even after the formation of full-depth cracks within 0.6 m thick clay barriers subjected to a maximum distortion level of 0.125. This observed behaviour is attributed to the downward thrust exerted by the deformed geomembrane at the zone of maximum curvature which hinders the infiltration of water through the cracks. The downward thrust exerted by the geomembrane on the clay barrier was found to be more for barriers provided with stiffer and thicker geomembrane.

Expansive clays undergo large volumetric changes with varying moisture content inducing desiccation cracks. Desiccation cracks increase the hydraulic conductivity and reduce the strength of the soil substantially. This can be a setback when expansive clays are used as landfill liners and covers where low hydraulic conductivity is mandatory to ensure a safe barrier. In this study, the effect of discrete and randomly distributed fiber (DRDF) reinforcement on desiccation cracking of soil with varying fiber lengths was investigated. Black cotton soil, a locally available expansive clay, was reinforced with polypropylene fibers of lengths 6, 12, and 18 mm, at 0.5% fiber content (% by dry weight of soil). The slurry samples were allowed to dry at uniform temperature and relative humidity. Various physical and morphological parameters such as cell area, crack width, and moisture content were observed over time. The crack parameters were quantified using digital image analysis (DIA). It was observed that fiber inclusion efficiently reduces desiccation cracking by increasing the tensile strength of the clay.

In situ shear strength parameters of rock mass are important design parameters required for design of structures founded on or constructed in rock mass. Block shear test method is quite popular among practicing engineers for determination of cohesion and friction angle of rock-to-rock and concrete-to-rock interface. Generally, at the stage of preliminary design, a value of desired shear strength parameters can be taken from available literature. However, such values must be used with proper engineering judgement. In case of rock mass, structural features of geology plays a very crucial role in affecting its engineering behavior. Same rock type may have significantly different shear strength parameters depending upon site-specific geological characteristics. In this paper, the variation in rock-to-rock and concrete-to-rock shear strength parameters of rock mass consisting of primarily granites is studied among three different geological variants, namely (a) western part of Himalaya, (b) Garo-Khasi Hills of Meghalaya, and (c) Eastern Ghat Belt of Andhra Pradesh. The variation in shear strength, cohesion, and friction angle is studied in terms of strength ratio, cohesion ratio, and friction angle ratio. These values are also compared with values for granites available in the literature. Site parameters supported with quantitative analysis of in situ data indicate that highest shear strength is expected at Eastern Ghat Belt and least shear strength at Garo-Khasi Hills.

Backfilling the mine voids with the suitable material can provide additional ground support by restricting lateral deformation of surrounding coal pillars and roof. This type of support mechanism helps to prevent caving, minimizes surface subsidence, and enhances pillar recovery. River sand is widely used as a stowing/backfilling material, as it is easily available and suitable for its geotechnical properties. River sand is in great demand for many construction projects and is in short supply in many areas. So it is highly desirable to find an alternative stowing material. Some alternative materials used for backfilling are waste rock, mill tailings, quarried rock, sand and gravel. Over the last decade, attention has been made on the use of coal combustion products as an alternate filling material for underground works. Usually, pond ash as a backfill material remains loose and serves only as a temporary working platform rather than offering any lateral strength. Adding low percentages of admixtures to backfill mass permits the development of cohesive strength and self-supporting ability during adjacent pillar mining. This self-supporting nature of the backfill permits higher recovery of pillar ore, which in turn improves the utilization of the mining reserve and the economics of the mining operation. In the present study, laboratory mine model was prepared by using pond ash as a backfilling material with different percentages of lime (2, 6, 8, and 10%) and gypsum (0.5, 1, 1.5, and 2%) as additives. To examine the effect of gypsum on the strength characteristics of stowed pond ash, core samples were collected from the model which were cured for different time periods such as 7, 14, and 28 days. To determine the engineering properties of pond ash composites unconfined compression tests as well as triaxial compression tests were performed. The increase in strength of pond ash composites was observed for lime content up to 6% and gypsum of 1.5%.

It is not unusual for the offshore deposits to carry loads in excess to their ultimate capacity, when these soils bear the loads of heavy oil platforms. These soils contain high calcium carbonate content, which make them prone to particle crushing at these high loads. This paper investigates the effect of particle breakage on the load response of offshore marine deposits. Two sea deposits off Mumbai coast were chosen for the tests. Both the soils had similar mineralogical composition. In this study, dilatancy was studied as a function of particle crushing at crushing stresses up to 4.5 MPa. A series of direct shear tests were performed on samples which were crushed to various loads. The experimental results showed that with increase in extent of crushing, dilatancy decreased up to a point and then increased. It also indicates that crushing takes place to a considerable extent even after settlements have reached a near-constant value. The decrease in dilatancy with increase in particle crushing was more pronounced in angular particles than sub-rounded and rounded particles. This was also confirmed from the SEM images. Stress–dilatancy equations of both the soils were developed using drained shear tests. Particle breakage seems to significantly affect the measured coefficient of friction and hence the dilatancy component.

Conventional investigation methods such as standard penetration test and cone penetration test fail to identify weak deposits like soft clay, and designing the foundation without identifying the presence of such layer and its strength is risky. Under the conditions stated, a simple field testing equipment is required to operate in such deposits and is also to be well suited for projects like road works, simple buildings. One such equipment is a light cone penetrometer (LCPT). Tests are done using LCPT at a few sites, and resistances are recorded over a depth of 6 m at each location. Resistances are also measured by conducting standard penetration test at location wherever LCPT was done. Correlation between LCPT and SPT resistances is developed. Simultaneously soil samples are collected from each location of LCPT and tested in laboratory for index properties and parameters such as shear strength, compressibility and field CBR. These soil parameters are correlated with the LCPT resistance individually.