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

The paper presents the results of three-dime2nsional finite element analysis of a single pile installed in homogeneous soft clay under individual lateral load and combined vertical and lateral loading. The interaction between vertical and lateral loads on piles has been analyzed using the finite element program GEOFEM-3D. In this analysis, the pile is treated as linear elastic and the behaviour of soil has been idealized using non-associated elastic perfectly plastic based Drucker-Prager constitutive model. The numerical results presented in this paper highlight the effect of vertical load interaction on the lateral load deflection response of pile with reference to some of the important parameters viz. method of loading, pile head fixity conditions and L/B ratio.

Department Of Civil Engineering

Proceedings of the 16th International Conference on Soil Mechanics and Geotechnical Engineering: Geotechnology in Harmony with the Global Environment

Interaction between vertical and lateral loads on the response of piles in soft clays

This note reexamines Biot's model for the propagation of acoustic waves in a material such as cohensionless sand, infused with a fluid, within the context of mixture theory. Instead of the standard entropy equation that is used in mixture theory, an inequality for the viscous dissipation is employed here due to a conceptual difficulty that one encounters in applying the standard equation to a mixture of sand and a fluid. The wave equations are reformulated by taking the velocity field, instead of the displacement, for the fluid as a primary quantity. By recognizing and thereby exploiting the dependence of the stored energy of the sand on the pore fluid pressure and choosing an appropriate form for the rate of dissipation, a set of governing equations are obtained which are equivalent to those derived by Biot [J. Acoust. Soc. Am. 28(1956) 168, 179; J. Appl. Phys. 33(1962) 1482]. A differential equation for the pore fluid pressure is derived and the effects of drag and virtual mass are dealt with in a unified fashion. The procedure allows us to develop generalizations to Biot's equations in a rational manner.

Department of Aerospace Engineering

International Journal of Non-Linear Mechanics

On the propagation of waves through porous solids

The response of an asphalt concrete pavement to external loading depends on its internal structure. Using a recent framework that associates different natural configurations (for example, stress-free configurations) with distinct internal structures of the body, we model asphalt concrete. We assume asphalt concrete to be a mixture of an aggregate matrix and an asphalt mortar matrix with evolving natural configurations. The evolution of the natural configuration is determined using a thermodynamic criterion, namely, the maximization of the rate of dissipation. Appropriate choices for the Helmholtz potential, the rate of dissipation and the other thermodynamic criteria are assumed to describe how energy is stored, the manner of the rate of dissipation, etc. As an example, we choose a specific form for the Helmholtz potential and the rate of dissipation function that leads to a generalized "upper convected Burgers's model," its linearized version being the viscoelastic model that is usually used for modeling asphalt concrete. This model is just an example of how a class of thermodynamically consistent models can be generated to describe the nonlinear behavior of materials such as asphalt concrete. We model the uniaxial compressive and tensile creep of asphalt concrete for two different types of specimens and test methods. We provide details of the numerical scheme we use to solve the initial value problem and we compare the experimental data of Monismith and Secor in 1962 with predictions of the model. © ASCE.

Journal of Materials in Civil Engineering

Thermodynamic framework for the constitutive modeling of asphalt concrete: Theory and applications

This study is concerned with the constitutive modeling of asphalt concrete mixtures. The constitutive model derived is based on a thermodynamic framework that recognizes the fact that materials can exist in multiple stress free states. We derive the constitutive relations by assuming that asphalt concrete is a constrained two constituent mixture of asphalt mastic and aggregate matrix. Assumptions are made concerning the manner in which the body stores and dissipates energy and the constitutive relations for the stress is deduced from such an assumption. The triaxial and stress relaxation tests conducted by Monismith and Secor [Viscoelastic behavior of asphalt concrete pavements. Report, Institute of Transportation and Traffic Engineering, University of California, Berkeley, 1962] are used as benchmarks to delineate the efficacy of the model in predicting the mechanical response characteristics of asphalt concrete over a wide range of temperatures and confining pressures. © 2003 Elsevier Ltd. All rights reserved.

Mechanics of Materials

Triaxial testing and stress relaxation of asphalt concrete

Some basic issues in constitutive modeling are examined. The first concerns the requirement of material frame indifference, the commonly used version is analyzed under the restriction that the effect of relativity is negligible. The second deals with the entropy production inequality in the modeling of large scale motions and the uncertainty involved in formulating such an inequality as a constraint in developing constitutive relations is discussed. Finally, the use of Lagrangian frames and reference configurations and related questions concerning the development of a constitutive model for turbulent flows of a fluid, on the basis of laminar flows of that fluid, is discussed. © 2003 Elsevier B.V. All rights reserved.

World University root node

Communications in Nonlinear Science and Numerical Simulation

Some issues in constitutive modeling

This paper presents the results of laboratory model tests carried out to study the relative performance of different forms of reinforcement (i.e. geocell planar and randomly distributed mesh elements) in sand beds under strip loading. The results demonstrate that geocell reinforcement is the most advantageous soil reinforcement technique of those investigated. With the provision of geocell reinforcement, failure was not observed even at a settlement equal to about 45% of the footing width and a load as high as eight times the ultimate capacity of the unreinforced soil, whereas, with planar reinforcement, failure took place at a settlement of about 15% of the footing width and a load of about four times the ultimate capacity of the unreinforced soil. For the case with randomly distributed reinforcement mesh, failure was recorded at a load of about 1.8 times the ultimate capacity of the unreinforced soil and at a settlement of about 10% o of the footing width. © 2004 Thomas Telford Ltd.

GENERAL

Geosynthetics International

Performance of different geosynthetic reinforcement materials in sand foundations

In this article, we provide a review of the uses of asphalt from ancient to modern times and we discuss the main attempts at mathematically modeling its behavior. We start with a discussion of the various definitions for asphalt and bitumen and discuss briefly some of the many fascinating uses to which they have been put from ancient to modern times. In Section 3 we survey the various attempts at unraveling the chemical structure of asphalt. The description of its physical characteristics, the early constitutive models that have been employed to describe its mechanical response, and the numerous tests to assess its properties are dealt with in Section 4. The next section is devoted to a discussion of the aging of asphalt. In Section 6, after a cursory discussion of the more classical models for asphalt concrete, we introduce the reader to a thermodynamic framework that has been recently put into place for bodies that have multiple natural configurations and use this framework to develop a model for describing the mechanical response of asphalt concrete. We use this model to describe various experiments that have been carried out on asphalt concrete and we find that the predictions of the model agree with experiments sufficiently well. This review article cites 580 references.

Applied Mechanics Reviews

Review of the uses and modeling of bitumen from ancient to modern times

All real bodies are inhomogeneous, though in many such bodies the inhomogeneity is "mild" in that the response of the bodies can be "approximated" well by the response of a homogeneous approximation. In this study we explore the status of such approximations when one is concerned with bodies whose response is nonlinear. We find that significant departures in response can occur between that of a "mildly" inhomogeneous body and its homogeneous approximation (if the approximate model is restricted to a certain class), both quantitatively and qualitatively. We illustrate this fact within the context of a specific boundary value problem, the inflation of an inhomogeneous spherical shell. We also discuss the inappropriateness of homogenization procedures that lead to a homogenized stored energy for the body when in fact what is required is a homogenized model that predicts the appropriate stresses as they invariably determine the failure or integrity of the body.

Journal of Elasticity

A comparison of the response of isotropic inhomogeneous elastic cylindrical and spherical shells and their homogenized counterparts

We have synthesized nanoporous carbon membranes that have monodisperse pores of 4-5 Å. These membranes have excellent size and shape selectivity that makes them an ideal candidate for use as separators in fuel cells. The selectivity of these membranes to gases such as N2, Q2 and water gas [carbon monoxide and hydrogen] were measured using a permeation testing unit. These membranes were then tested as separators in fuel cells.

Department Of Chemical Engineering

Materials Research Society Symposium - Proceedings

Using nanoporous carbon membranes in fuel cells

It is quite common to approximate “mildly” inhomogeneous bodies as homogeneous bodies belonging to a certain constitutive class in view of the simplification that such an approximation accords. In this study, we investigate the consequences of such an assumption and we show that it is clearly inappropriate for many classes of inhomogeneous bodies. We choose specific boundary value problems to illustrate the fact that we could be grossly in error, both qualitatively and quantitatively, with regard to local measures such as stresses and strains. In the examples considered, we find that, for global quantities such as applied forces and moments, the error could be significant. Not only could the material parameters found from, say, an extension test and torsion test, which neglect the inhomogeneity of the body, be quite different from one that incorporates the inhomogeneity, but also the values for the material parameter in the homogenized approximation gleaned from these different experiments could be different. In the process of elucidating our thesis, we investigate an important class of deformations, which in view of the paucity of boundary value problems that have been solved for non-linear inhomogeneous solids is worth documenting in its own right.

On the Role of Inhomogeneities in the Deformation of Elastic Bodies

Different kinds of hot mix asphalt mixtures are used in highway and runway constructions. Each of these mixtures cater to specific needs and differ from each other in the type and percentage of aggregates and asphalt used, and their response can be markedly different. Constitutive models used in the literature do not differentiate between these different kinds of mixtures and use models which treat them as if they are one and the same. In this study, we propose constitutive models for two different kinds of hot mix asphalt, viz., asphalt concrete and sand asphalt. We use a framework for materials that possess multiple natural configurations for deriving the constitutive equations. While asphalt concrete is modeled as a two constituent mixture, sand asphalt is modeled as a single constituent mixture due to the peculiarity in its makeup. In this study, we present a unified approach for deriving models for these different kind of mixtures. In a companion paper, we compare the predictions of the model for a compressive creep test with available experimental results. Copyright © 2002 by ASME.

ASME International Mechanical Engineering Congress and Exposition, Proceedings

Constitutive modeling of asphalt bound granular materials - Theoretical background

We propose a thermodynamic framework for describing the microwave drying process of aqueous dielectrics based on Maxwell-Lorentz field equations and mixture theory. Several issues are discussed such as the form of entropy equation; the constitutive relations for the macroscopic electric polarization vectors, Cauchy stresses, heat fluxes, internal momentum supplies, etc., for each component of the mixture: porous solid, water and gas in different regions; and the interfacial jump conditions between different regions in the mixture. A brief examination of the status of material frame indifference within the context of our framework is presented.

Zeitschrift fur Angewandte Mathematik und Physik

Modeling of the microwave drying process of aqueous dielectrics

The strength improvement due to the provision of sand layers on either side of the reinforcement (sandwich technique) within reinforced clay soils is studied in this paper. The behaviour of reinforced clay was examined in triaxial compression tests under both static and cyclic loading conditions. Effect of the sand layer thickness, moisture content and reinforcement types were studied. Three different types of reinforcements, namely, woven geotextile, non-woven geotextile and micro-grid were used. All the triaxial compression tests were conducted under unconsolidated-undrained (UU) conditions. The results of the tests indicate that a thin layer of high-strength sand provided on both sides of the reinforcement is effective in improving the strength and deformation behaviour of reinforced clay soils under both static and cyclic type loadings. © 2002 Elsevier Science Ltd. All rights reserved.

Geotextiles and Geomembranes

Behaviour of reinforced clay under monotonic and cyclic loading

This note presents a random walk formulation of small particle tracking within the framework of averaged turbulence modeling. Several issues, such as a justification for the finite number of multi-point correlations to be taken, the adoption of just one two-point correlation rather than several, and construction of specific models, are discussed. It offers a new perspective on random walk modeling of small particle dispersion and suggests some possible improvements to existing models, especially with regard to taking into account the spatial correlation explicitly. © 2002 Published by Elsevier Science B.V.

A new perspective on random walk modeling of particle dispersion

In the earlier paper, we developed constitutive relations for two kinds of hot mix asphalt, viz., asphalt concrete and sand asphalt using the framework of materials with multiple natural configurations. In the present paper, we apply the framework that we developed for sand asphalt to study compressive creep experiments. Experimental studies ofWood and Goetz (1959) are used to compare with the predictions of the model. Copyright © 2002 by ASME.

Constitutive modeling of asphalt bound granular materials - Applications to sand asphalt

This paper describes the measurement of strains in the side walls of geocells supporting laboratory models of embankments constructed on soft clay foundations. Model embankments were constructed over a layer of geocells formed on top of the soft clay bed prepared in a steel test tank. The stiffness of the geogrid used to make the geocells, dimensions of the cells, aspect ratio of cells and the length of geocell layer were varied in different model test. Strains in the walls of the geocells at different levels of surcharge pressure applied on the crest of the embankment were measured through strain gauges fixed to the walls of geocells using a strain meter. These strains have given clear insight about the performance of the model embankment and were used to estimate the "apparent" cohesive strength of the geocell layers in various model embankments.

Geosynthetics Conference 2001

Measurement of strains in geocells supporting an embankment

This paper presents the results from laboratory-model tests on a strip footing supported by a sand bed reinforced with a geocell mattress. The parameters varied in the testing program include pattern of geocell formation, pocket size, height and width of geocell mattress, the depth to the top of geocell mattress, tensile stiffness of the geogrids used to fabricate geocell mattress and the relative density of the sand. With the provision of geocell reinforcement, failure was not observed even at a settlement equal to 50% of the footing width and a load as high as 8 times the ultimate bearing capacity of the unreinforced sand. Based on the model test results, the depth of placement and the dimensions of the geocell layer for mobilising maximum bearing capacity improvement have been determined. In addition to the tensile strength of reinforcement, the aperture size and orientation of ribs of the geogrid used to fabricate geocell mattress must be taken into account while evaluating its contribution to the improvement in the performance. © 2001 Elsevier Science Ltd. All rights reserved.

Bearing capacity of strip footings supported on geocell-reinforced sand

We propose a framework to describe the mechanical behavior of thermally damaged biological soft tissues based on a melding of ideas from classical continuum thermodynamics and irreversible thermodynamics. Relevant assumptions are delineated, details of the constitutive formulation are provided, and a set of interfacial conditions are derived that can be used as the boundary conditions for certain diffusion processes. The utility of the framework is illustrated by considering two problems that correspond to tractable experiments: transverse diffusion through a finitely deformed membrane, and radial diffusion in a thermally damaged cylindrical tissue. © 2001 Elsevier Science Ltd.

International Journal of Engineering Science

A mixture theory for heat-induced alterations in hydration and mechanical properties in soft tissues

Despite the intense effort expended towards obtaining a model for describing the turbulent flows of fluid, there is no model at hand that can do an adequate job. This leads us to look for a non-traditional approach to turbulence modeling. In this work we conjoin the notion of large eddy simulation with those of fuzzy sets and neural networks to describe a class of turbulent flows. In previous works we had discussed several issues concerning large eddy simulation such as filtering and averaging. Here, we discuss the use of fuzzy sets to improve the filtering procedure.

Discrete large eddy simulation

The results from laboratory model tests on strip footings supported by geocell reinforced sand beds with additional planar reinforcement are presented. The test results show that a layer of planar geogrid placed at the base of the geocell mattress further enhances the performance of the footing in terms of the load-carrying capacity and the stability against rotation. The beneficial effect of this planar reinforcement layer becomes negligible at large heights of geocell mattress. © 2001 Elsevier Science Ltd. All rights reserved.