IIT Madras is a public technical and research university located in Chennai, Tamil Nadu. Founded in 1959, it is recognised as an Institute of National Importance.

IIT Madras has been ranked as the top engineering institute in India for four years in a row by the National Institutional Ranking Framework of the MHRD

It currently offers undergraduate, postgraduate and research degrees across 16 disciplines in Engineering, Sciences, Humanities and Management. About 596 faculty belonging to science and engineering departments and centres of the Institute are engaged in teaching, research and industrial consultancy.

IIT Madras

Clay deposits often exhibit inherent anisotropy due to different microfabrics, resulting from both environmental conditions during deposition and stress conditions subsequently. Many anisotropic elastic-plastic models are developed for modeling the behavior of clays subjected to anisotropic stress conditions. In this study, the drained and undrained shearing behavior of kaolinite clay samples with different microfabrics are modeled using anisotropic S-CLAY1 model with a rotational hardening rule and the isotropic modified cam clay (MCC) model. The inherent anisotropy resulting from the difference in the microfabric of the clay samples, reflected as the initial value of the rotational hardening parameter of the S-CLAY1 model, is determined based on the shape of the undrained stress paths of the samples subjected to consolidated undrained triaxial tests. The simulated results are compared with the results of consolidated undrained and drained triaxial tests carried out on kaolinite samples with different microfabrics. Clay samples with different microfabrics are prepared artificially, in the laboratory, by remolding with different pore fluids. It is observed that while S-CLAY1 model predicts the undrained behavior of kaolinite samples better, the drained behavior is better predicted by the MCC model. © 2014 W. S. Maney & Son Ltd

Department Of Civil Engineering

International Journal of Geotechnical Engineering

Undrained and drained shearing behavior of kaolinite with different microfabrics

The post-cyclic behaviour of a clayey soil after subjecting to cyclic loading is presented in this paper. Tests were carried out on the samples both by allowing the cyclic pore pressure developed during cyclic loading to dissipate and without dissipation. While the samples subjected to post-cyclic monotonic loading without dissipation of cyclic pore pressure exhibited a highly overconsolidated behaviour, the samples after dissipation of cyclic pore pressure exhibited a lightly overconsolidated behaviour. All the samples subjected to cyclic loading exhibited a higher undrained strength during post-cyclic monotonic tests, when compared to the samples without prior cyclic loading history. Post cyclic consolidation tests depicts that the samples show signs of apparent over-consolidation. © 2013 Indian Geotechnical Society.

Indian Geotechnical Journal

Post-Cyclic Behaviour of Clayey Soil

Expansive soils have the tendency to undergo volume change behavior and cause large uplift pressures and upheaval of structures built on them. Avoiding expansive soil in most of the cases is not practically possible, hence stabilization practices are undertaken to treat them. Chemical stabilization through lime is the most sought after treating method. In this study, soil from an expansive soil site, Siruseri near Chennai, was treated with lime to understand the microstructural changes taking place and its influence on the macro structural properties. X-ray diffraction, SEM and microporosimetry were the techniques used to understand the microstructural properties of lime treated soils. The expansive soil was treated with different percentage of lime, 2, 4, 6, and 8 % and cured for 3, 7, 14, and 28 days. The concept of lime modification optimum (LMO) was used as a reference to understand the progression of lime reactions. The change in the physical properties of the soil was determined through UCC, chemical batch testing, pH and chemical conductivity. The lime addition higher than the LMO brings about more permanent pozzolanic reactions which cause tremendous increase in strength. The time dependency of the reactions was observed through the change in pH values, conductivity and batch test results. At the microstructural level, lime addition reduces the specific surface area and increases the pore size. The SEM results also revealed larger clusters and aggregation of the clay particles. © 2013 Indian Geotechnical Society.

Behaviour of Lime Treated Cured Expansive Soil Composites

Clays treated with lower cement contents often exhibit behaviour similar to stiff clays with planar failure surface under triaxial compression. In the present work the behaviour of a marine clay treated with 5 % cement, subjected to undrained triaxial compression tests is studied. The pre-consolidation pressure of the cemented clay due to the cementation bonding is observed to be very high. It is attempted to model the behaviour of cement treated clay using a bounding surface plasticity formulation as the plastic behaviour of the cemented clays within the yield surface has to be considered. The effect of cementation is included in the model as the pre-consolidation pressure obtained from consolidation tests. The tensile strength due to cementation bonds is included in the equation of the bounding surface. Simulations of the undrained triaxial compression tests on cemented clays are carried out and the results are validated with the experimental results. © 2012 Springer Science+Business Media Dordrecht.

Geotechnical and Geological Engineering

Undrained Triaxial Behavior of Cement Treated Marine Clay

Determination of critical state parameters are essential, when critical state soil mechanics based soil models are used for the analysis. Isotropic consolidation test and triaxial tests with accurate measurements of volume change and pore pressure are essential for the direct measurement of critical state parameters. However, in the conventional geotechnical engineering practice, isotropic compression tests are usually not conducted but only one-dimensional consolidation test are performed. The usual parameters reported in most of the soil investigation reports are the shear strength parameters c′ and φ{symbol}′ and the consolidation parameters such as compression index (Cc) and the recompression index (Cr) apart from, the overburden pressure σ0′ and the corresponding void ratio e0. The critical state parameters are seldom reported in most of the soil investigation reports. This paper explains a procedure to estimate the critical state parameters, in the absence of isotropic compression test data, based on one-dimensional consolidation tests and triaxial compression tests, using the equations of Modified Cam clay state boundary surface. Comparison of the calculated values from the suggested method with the measured values, on three reconstituted soils and one undisturbed soil, lends support to the validity of the proposed procedure. © 2013 Indian Geotechnical Society.

Estimation of Critical State Parameters from One-dimensional Consolidation and Triaxial Compression Tests

The flexible wall permeability apparatus was modified for the direct measurement of the hydraulic conductivity of soils in the horizontal direction. Constant head permeability tests were carried out using the radial flow flexible wall permeameter on soil samples with central sand drain to allow the water to flow radially from the central sand drain towards a peripheral drain. Tests were also conducted using the conventional flexible wall permeameter on samples that were trimmed horizontally, so as to measure the hydraulic conductivity in the horizontal directions for comparison. The test results obtained from the proposed setup agrees well with those obtained from the samples that were trimmed horizontally, proving the validity of the results obtained from the proposed apparatus. Copyright © 2013 by ASTM International.

Geotechnical Testing Journal

Flexible wall permeameter to measure the hydraulic conductivity of soils in horizontal direction

The in-situ deep cement mixing method is an established technique for improving the strength and reducing settlement of soft soil deposits. In practice, upon completion of the cement treatment, the improved ground will be left for curing over a specific period of time, before commencement of construction activities. In the case of deep mixing, curing takes place under the overburden pressures, at deeper depths. Studies on the influence of curing stress on the stress-strain and strength characteristics of cement stabilized clays are limited. The role of curing stress on the strength behavior of the cement treated soil is studied in this paper. Consolidated undrained triaxial compression tests performed on cement treated samples cured with and without stress are mainly focused. Marine clay from Ennore, near Chennai, India, excavated at a depth of 1.5 m was selected for the study. The range of cement contents selected were 10%, 15% and 20% with curing time of 28 days. The curing stresses adopted were 0, 50, 100 and 200 kPa. Additional tests were also conducted to study the effect of lower cement content of 5% and the effect of higher confining pressures. J. Ross Publishing, Inc. © 2012

Shear strength behavior of cement treated marine clay

Vacuum preloading of clay deposits is becoming an increasingly popular ground improvement technique. Although many studies have been reported in literature, the mechanism of vacuum preloading is still not properly understood. Soil under vacuum preloading is expected to undergo an inward lateral deformation, therefore the influence of lateral deformation on volumetric strain requires further analysis. This paper addresses this aspect through laboratory studies on reconstituted samples of kaolinite. The Rowe cell apparatus was modified to measure lateral deformation under various states of stress because lateral and vertical deformation of soil depends on its state of stress and associated lateral pressure. A method for predicting the volumetric and lateral strains under vacuum consolidation is proposed and then applied to two case studies in China.

Canadian Geotechnical Journal

Final state of soils under vacuum preloading

Stone columns are often considered as an excellent ground improvement technique adopted to improve the load carrying capacity and reduces the settlement characteristics. However the load carrying capacity mainly depends on the undrained shear strength of surrounding soils. Reinforcement in the form of encasement is usually provided around the stone columns which imparts lateral confinement, resulted in improved load carrying capacity. This geosynthetic encasement also acts as an excellent filter, prevents the entry of finer clay particles and offers better drainage path for pore water dissipation. Vacuum consolidation is a type of preconsolidation technique in which vaccum is applied through PVD's in a sealed membrane system. The applied vacuum creates negative pore pressure which increases the effective stress without altering the total stresses. The improvement in effective stress thus leads to increase in undrained shear strength of clay soils. The research work involves application of vacuum through encased stone columns and tests done to study the improvement in load carrying capacity of encased stone column after vacuum application. Soil samples after the vacuum consolidation were also taken to study the increase in undrained shear strength after vacuum application.

GA 2012 - 5th Asian Regional Conference on Geosynthetics: Geosynthetics for Sustainable Adaptation to Climate Change

Stabilisation of soft clays using geosynthetic encased stone columns with vacuum application

Journal of Geotechnical and Geoenvironmental Engineering

Closure to "Effect of Microfabric on Undrained Static and Cyclic Behavior of Kaolin Clay" by Rakesh J. Pillai, R. G. Robinson, and A. Boominathan

Vertical drains are extensively used to accelerate the consolidation of soft clay deposits when preloading is used as a ground improvement technique. Barron's theory is widely adopted for the design of vertical drains. The important input parameter required in Barron's solution is the coefficient of radial consolidation (cr) and a rational assessment of cr is necessary for the economic design of vertical drains. Several methods are available for the determination of the coefficient of consolidation (cv) under vertical drainage. However, very few methods were developed for the determination of cr. The √t method and log t method are considered as standard methods and are commonly used in practice for the determination of cv. The utility of √t method for the determination of cr is attempted in the literature. However, no attempt has been made in the literature to use the other standard method, the log t method, for the determination of cr. In this paper, the log t method is proposed for the determination of cr from the time-compression data obtained from consolidation tests under radial drainage. The validity of the method is evaluated by matching the experimental data with the theory and comparing with the existing methods. J. Ross Publishing, Inc. © 2011

Determination of radial coefficient of consolidation using log t method

Microfabric plays an important role in the engineering behavior of soils. Although many studies are available in the literature on the effect of microfabric on the static behavior of soils, the effect on the cyclic behavior is less understood. In the present study, samples with different microfabric were prepared in the laboratory by reconstituting commercially available kaolin clay with different pore fluids under a consolidation pressure of 100 kPa. Consolidated undrained triaxial tests were carried out on these samples under static and cyclic loading conditions. Dispersed samples were found to have monotonic stress-strain behavior with a peak deviatoric stress and higher peak undrained shear strength than the flocculated samples. However, the dispersed samples were found to offer less resistance to cyclic loading. When subjected to cyclic loading, dispersed samples failed within a few cycles under a cyclic stress ratio (defined as the ratio of cyclic deviatoric stress to the undrained shear strength) close to 0.6, whereas in flocculated samples, sudden failure was not observed even at a higher cyclic stress ratio of 0.9, although strains and pore pressures accumulated to higher values. Postcyclic monotonic tests conducted on samples that did not fail under cyclic loading showed an apparent overconsolidation effect caused by cyclic loading in a similar manner, as reported in the literature. © 2011 American Society of Civil Engineers.

Effect of microfabric on undrained static and cyclic behavior of kaolin clay

Vacuum preloading technique is a viable ground improvement technique for the stabilization of soft grounds. The basic difference between surcharge preloading and vacuum preloading is that surcharge preloading imparts anisotropic stress conditions to the soil whereas the stress induced by vacuum pressure is more close to isotropic as it is applied to the pore phase. Therefore, the soil deform in the outward direction in the former case where as it is inward in the latter case. Though vacuum consolidation technique is extensively used in practice, the mechanism of soil deformation is not properly evaluated in the literature. This paper examines this aspect through an experimental programme on a reconstituted soil using a double wall triaxial cell. Apart from monitoring the vertical deformation, the lateral strain was also computed. It was found that the vertical settlement under vacuum consolidation is less than that obtained from one-dimensional consolidation under the same consolidation pressure. The vertical settlement under vacuum pressure is same as that under equivalent surcharge loading, if 1-D condition prevails. Copyright © 2009 by Geotechnical Society of Singapore (GeoSS).

Geotechnical Society of Singapore - International Symposium on Ground Improvement Technologies and Case Histories, ISGI'09

Deformation behaviour of soil under vacuum consolidation

This paper describes the microfabric and mineralogical changes in an expansive soil from Siruseri (South-East Chennai, Tamilnadu, India), when treated with inorganic additives such as Calcium Hydroxide and Calcium Chloride. The engineering and index properties and mineralogical composition of the untreated and treated soil were determined. The soil particles have been found to get altered and new products are formed in the case of the calcium hydroxide treated samples. The fabric becomes more flocculated and the microfabric results indicate the formation of new aggregations and bindings due to the addition of the stabilizer. The X-ray diffraction tests on the treated samples indicated a shift in the basal spacing and reduction in peak intensities which is due to the formation of the flocculated structure. This shows that the stabilizing effect of an effective additive brings a change in the microfabric and mineralogy, which causes a change in the engineering and index properties of the original soil. The effects of both the stabilizers are studied and a comparative study is made. Calcium hydroxide brings more desirable effects due to the pozzolanic reactions and formation of cementitious products such as the calcium silicate hydrate (CSH) and calcium aluminate hydrate (CAH). The addition of CaCl2 makes the soil denser and forms denser clay matrices and there is no pozzolanic reaction. In order to cater the problem of solubility in the case of lime column usage for deeper depths, attempt was made to study the influence of the addition of lime solution to the expansive soil. The addition of lime solution reduced swelling but the engineering properties did not change significantly. J. Ross Publishing, Inc. © 2010

Micro-fabric and mineralogical studies on the stabilization of an expansive soil using inorganic additives

Yield stress is one of the most important properties of soils. This paper addresses the yield stress of a desiccated expansive soil that was subjected to repeated cycles of wetting and drying under controlled laboratory conditions. Identical samples were subjected to different surcharge pressures such as 6.25, 12.5, 25, 50, 100 and 200 kPa so as to simulate the depth in the field. The samples were dried up to equilibrium at a temperature of 40 ± 5°C, in a thermostat controlled oedometer. Wetting was done by submerging the samples under water. The movements during wetting and drying were recorded and it was found that equilibrium is reached in about five cycles. After reaching equilibrium, samples were unloaded to a seating pressure of 6.25 kPa and conventional one-dimensional consolidation testwas conducted. The experimental results showthat the yield stress of desiccated expansive soil depends on the surcharge pressure. The overconsolidation margin, which is the difference between the yield stress and the effective vertical stress, of desiccated expansive soil is almost constant of about 100 kPa. This suggest that desiccation induced yield stress is similar to overburden pressure in the geological past. © 2010 Taylor & Francis Group, London.

World University root node

Unsaturated Soils: Theoretical and Numerical Advances in Unsaturated Soil Mechanics - Proceedings of the 4th Asia Pacific Conference on Unsaturated Soils

Consolidation behaviour of a desiccated expansive soil

Expansive soils cover about 20% of the land area of India. These soils undergo volume change due to moisture fluctuations. Therefore, lightly loaded structures and pavements are often severely affected. While several chemical stabilization techniques are available to treat these soil deposits, under-reamed piles are often used as a foundation alternative. One to two bulbs of diameter larger than the stem diameter of the piles are provided below the unstable zone. One of the important aspects of the design of underreamed piles is the estimation of uplift force that gets generated due to heaving of the soil within the active zone. Quite often, the tensile forces developed on the shaft of the pile due to heaving of soil can be high enough to crack the pile shaft. An understanding of the uplift force on the pile is therefore very important. The uplift force on the pile depends on the interface friction of the pile and the magnitude of swell. Interface direct shear tests were conducted to determine the interface friction between soil and concrete surface. Oedometer swell tests were also conducted to evaluate the magnitude of swell under different surcharge pressures. The PIES (Piles in Expansive Soils) program, developed in the University of Sydney, Australia, was used to study the behaviour of piles. The results indicate that the uplift force on the pile is not constant, as is normally assumed in the design, but initially increases to reach a maximum. After reaching the maximum, the uplift force decreases as the depth increases. Parametric studies have been done to understand the influence of load on pile and the influence of swelling pressure of soil on the pile uplift behaviour for a case study. © 2010 CAFET-INNOVA TECHNICAL SOCIETY. All rights reserved.

International Journal of Earth Sciences and Engineering

Uplift forces on piles in expansive soil

The cyclic swell shrink behaviour of expansive soils due to alterations in moisture content causes extensive distress to structures found on them. The volume change behaviour of the lime column stabilized expansive soil, under repeated wetting and drying is studied in the present investigation. The tests are carried out in modified oedometer cells at controlled temperature of 40 ± 5°C for faster drying. Diameter ratio of soil to lime column was varied and different techniques were adopted to improve the rate of diffusion. Microstructure observations were made through Scanning Electron Microscope studies. The equilibrium magnitude of swell-shrink is reached after about six to seven cycles. The lime column takes at least two cycles to get diffused into the surrounding soil to curtail the swelling. The subsequent shrinkage induced cracks enabled faster diffusion into the soil. © 2010 Taylor & Francis Group, London.

Cyclic swell-shrink behavior of lime column stabilized expansive soil

Response to discussion of "analysis of radial consolidation test data using a log-log method" by Robinson, R.G.

Vertical drains are extensively used to accelerate the consolidation of soft clay deposits. Barron's theory is usually used to analyze this problem, in which the drainage occurs in the radial direction. The important input parameter in Barron's theory is the coefficient of radial consolidation (cr) and a rational assessment of cr is necessary for the economic design of vertical drains. While several methods exist for the determination ofthe coefficient of consolidation (cv) under vertical drainage, very few methods are available for the determination of Cr In this paper, a log-log method is proposed for the determination of Cr from the experimental data obtained from consolidation tests under radial drainage, based on the characteristic feature observed from a log Ur versus log Tr plot for the equal strain condition. The validity of the method is evaluated by comparing the experimental data with the theory and comparing with the existing methods, such as the √t method and the inflection point method. In addition, the parameters obtained based on the proposed method are used to analyze a large-scale experiment with a prefabricated vertical drain. Copyright © 2009 by ASTM International.

Analysis of radial consolidation test data using a log-log method

Swelling pressure of clays is an important parameter required for the design of a variety of structures founded on expansive soils. Out of many methods available to determine the swell pressure in the laboratory, odometer method is popular because of its simplicity. Three odometer methods are commonly used to determine swelling pressure, such as swell consolidation method (Method A), different pressure method (Method B) and constant volume method (Method C). Comparison of values obtained by the three methods shows that Method A gives highest value, Method B gives the lowest value and Method C give intermediate value. The possible reason for this difference is brought out in this paper. Experimental evidence, from permeability measurements and SEM, shows that fabric alteration from a flocculated state to dispersed state occur in Method A due to swelling under a nominal surcharge pressure. As swelling is not permitted in Method B and C, the original fabric remains the same. J. Ross Publishing, Inc. © 2009