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

GENERAL

Department Of Civil Engineering

Journal of Structural Engineering (Madras)

A note on probabilistic seismic hazard assessment for Chennai, India

Chennai city suffered moderate tremors during the 2001 Bhuj and Pondicherry earthquakes and the 2004 Sumatra earthquake. After the Bhuj earthquake, Indian Standard IS: 1893 was revised and Chennai city was upgraded from zone II to zone III which leads to a substantial increase of the design ground motion parameters. Therefore, a comprehensive study is carried out to assess the seismic hazard of Chennai city based on a deterministic approach. The seismicity and seismotectonic details within a 100 km radius of the study area have been considered. The one-dimensional ground response analysis was carried out for 38 representative sites by the equivalent linear method using the SHAKE91 program to estimate the ground motion parameters considering the local site effects. The shear wave velocity profile was inferred from the corrected blow counts and it was verified with the Multichannel Analysis of Surface Wave (MASW) test performed for a representative site. The seismic hazard is represented in terms of characteristic site period and Spectral Acceleration Ratio (SAR) contours for the entire city. It is found that structures with low natural period undergo significant amplification mostly in the central and southern parts of Chennai city due to the presence of deep soil sites with clayey or sandy deposits and the remaining parts undergo marginal amplification. © Printed in India.

Journal of Earth System Science

Seismic hazard assessment of Chennai city considering local site effects

The traditional factor of safety does not account for the variability and uncertainty of the different parameters considered in the analysis. On the other hand, the reliability approach considers the possible variations in the design parameters and gives more realistic estimates of the safety of the structure and the possible risk of failure. In the present investigation, reliability analysis was carried out to study the stability aspects of reinforced soil retaining walls under static and seismic conditions using three methods: first-order second-moment method (FOSM), point estimate method (PEM) and first-order reliability method (FORM). A parametric sensitivity analysis is presented to bring out the effect of uncertainties in the soil and reinforcement parameters on the value of the minimum reliability index for internal and external stability of reinforced soil walls under static and seismic loads. The reliability indices evaluated by the three methods of reliability analyses were compared for both the internal and external stability of the wall. Based on the results, it is concluded that the friction angle (φ) is the most sensitive random variable affecting the overall stability of the reinforced soil walls under static and seismic loads. © 2008 Thomas Telford Ltd.

Geosynthetics International

Reliability analysis of reinforced soil walls under static and seismic forces

This paper presents an alternative numerical method to model the two-dimensional contaminant transport through saturated porous media using a meshless method called Element Free Galerkin Method (EFGM). In EFGM, an approximate solution is constructed entirely in terms of a set of nodes and no elements or characterization of the interrelationship of the nodes is needed to construct the discrete equations. For analysis, the two-dimensional advection-dispersion equation with sorption is considered. The unknown concentration values are approximated by using moving least square approximants, which are constructed using a weight function, a linear basis function and a set of non-constant coefficients. A weak form of the governing equation is formulated and Lagrange multiplier method is used for enforcing the essential boundary conditions. MATLAB code is developed to obtain the numerical solution. Two numerical examples are presented to illustrate the applicability of the proposed method and the results are compared with those obtained from the finite element method. Copyright ASCE 2008.

Geotechnical Special Publication

Two-dimensional contaminant transport modelling using meshless method

This paper presents a new numerical tool to model two-dimensional contaminant transport through unsaturated porous media using a meshfree method, called the Element Free Galerkin Method (EFGM). In the EFGM, an approximate solution is constructed entirely in terms of a set of nodes and no characterization of the interrelationship of the nodes is needed. The advection-dispersion equation with sorption is considered to illustrate the applicability of the EFGM. The Galerkin weak form of the governing equation is formulated using 2D meshfree shape functions constructed using moving least square approximants, which are constructed by using a weight function, a linear basis function and a set of non-constant coefficients. MATLAB code is developed to obtain the numerical solution. Two numerical examples are presented and the results are compared with those obtained from the finite element method. © 2008 Taylor & Francis Group, London.

Unsaturated Soils: Advances in Geo-Engineering - Proceedings of the 1st European Conference on Unsaturated Soils, E-UNSAT 2008

Meshfree modelling of two-dimensional contaminant transport through unsaturated porous media

This paper deals with the application of a meshless method called element-free Galerkin method (EFGM) for modelling the contaminant transport through the unsaturated porous media with transient flow condition. In EFGM, an approximate solution is constructed entirely in terms of a set of nodes and no elements or characterization of the interrelationship of the nodes is needed to construct the discrete equations. For analysis, the one-dimensional form of advection-dispersion equation with linear first-order degradation is considered. The unknown concentration values are approximated by using moving least square approximants. The weak form of the governing equation is formulated and the Lagrange multiplier method is used for enforcing the essential boundary conditions. The van Genuchten model is used for describing the hydraulic properties of the unsaturated soil. MATLAB code is developed to obtain the numerical solution. Numerical examples representing various phenomena that occur during the migration of contaminants are presented to illustrate the applicability of the proposed method and the results are compared with those obtained from the finite element method and the analytical solution.

Geomechanics and Geoengineering

Meshfree modelling of one-dimensional contaminant transport in unsaturated porous media

This paper presents the analysis of elastically supported beams using the element free Galerkin method (EFGM). The elastic support can be provided in the form of a load-bearing medium such as soil, distributed continuously along the length of the beam. This type of supports can be found in a variety of engineering problems, for example in the case of actual foundations or in the case of railroad track. The main difficulty in the analysis of the soil foundation interaction lies in the determination of the contact pressure. Any constitutive models may be used for simulating the action of the soil media. The finite element method has been used to model the beams on elastic foundations by representing continuity of the soil medium. However, the computations involved are more and has limited practical applications. In this paper, an attempt has been made to provide a simple but sufficiently accurate model for beams on elastic foundations using the meshfree technique, called as element free Galerkin method which does not rely on mesh. The formulation for the beams on elastic foundation is given for the governing equation which treats the soil in the form of rows of closely spaced independent elastic springs. The EFGM presented in the paper employs generalized moving least square approximants to approximate the function and transformation method for imposing the essential boundary conditions. Numerical examples are provided to study the convergence with various loading and boundary conditions. The results of the proposed method are compared with analytical solutions.

Element free Galerkin method for beams on elastic foundation

One of the forms of natural disasters given much attention by researchers all over the world during the International Decade for Natural Reduction (1990-2000) is the occurrence of landslides. Landslides take place in various regions of India, notably in the Himalayas and the Western Ghats, especially during monsoon. This paper describes some of the on-going studies related to modelling and risk evaluation of landslides at IIT Bombay, India. The studies describes are: (i) rainfall induced landslide evaluation using DEM and GIS, (ii) fractal modelling of mass movement including critical failure surface determination using shortest path concept of GIS and (iii) evaluation of risk due to landslide. The unconventional methods used here demonstrate the usefulness of a GIS based technique in identifying potential slide regions in a long stretch of a hill slope and the corresponding risk, which could serve as supports for landslide hazard management.

World University root node

International Geoscience and Remote Sensing Symposium (IGARSS)

Landslide modelling using remote sensing and GIS

The stability assessment of slopes is difficult because of many uncertainties. Possibilistic approach using fuzzy sets allows for a logical and systematic analysis of the uncertainties. In this paper an attempt has been made to present a new approach for the stability analysis of slopes incorporating fuzzy uncertainty. Uncertain parameters are expressed as fuzzy sets. A methodology has been presented in the study to process the fuzzy uncertainties in a slope reliability analysis. Fuzzy uncertainty i s incorporated in the estimated probability of failure. A numerical example of the finite earth slope problem illustrates the methodology. The approach allows assessment of the likelihood that a particular slope section will have a higher failure probability than the failure probability of the 'critical' deterministic failure surface. (C) 2000 Elsevier Science Ltd. All rights reserved.The stability assessment of slopes is difficult because of many uncertainties. Possibilistic approach using fuzzy sets allows for a logical and systematic analysis of the uncertainties. In this paper an attempt has been made to present a new approach for the stability analysis of slopes incorporating fuzzy uncertainty. Uncertain parameters are expressed as fuzzy sets. A methodology has been presented in the study to process the fuzzy uncertainties in a slope reliability analysis. Fuzzy uncertainty is incorporated in the estimated probability of failure. A numerical example of the finite earth slope problem illustrates the methodology. The approach allows assessment of the likelihood that a particular slope section will have a higher failure probability than the failure probability of the 'critical' deterministic failure surface.

Computers and Geotechnics

Reliability analysis of slopes using fuzzy sets theory

Socket resistance contributes significantly to pile capacity. In the present work, and approach is presented for estimating the capacity of side-resistance-only piles socketed in rock by considering the effect in terms of JRC and Fractal Dimension. Unlike available methods of quantification of roughness of surfaces, Fractal geometry allows the description of irregular shapes. A correlation is established between JRC and Fractal Dimension (D). This is used to estimate socket contribution and predict pile capacity based on an iterative procedure. Here the axial load is calculated by incrementing vertical displacement along the interface and estimating the shear strength mobilised at the interface using above correlation. Pile socket data reported in literature is used for validating the approach. The study is then extended to piles in weathered rock in Mumbai region. The results show that it is feasible to make a reliable estimate of the socket strength contribution.