G R Dodagoudar

Peninsular India is known for its complex intraplate seismicity and the southern part of it is characterized by diffused and distributed seismicity. In such cases the most commonly adopted seismic source is the area source zone. The formation of seismic area source zone is subjective for regions such as south India and hence zonefree techniques to probabilistic hazard analysis have been carried out in the past. The zonefree technique specifically the kernel technique is still new and has been applied to specific sites in south India such as Chennai and Kanchipuram. In this study the fixed and adaptive kernel techniques have been applied to the whole of south India to obtain the hazard value. The most influencing parameter affecting the kernel technique has been varied in two ways - the bandwidth parameters determined for the whole earthquake catalogue of south India and the other by determining the bandwidth parameters for the earthquakes lying in an influence area of 300 km radius around a particular site. It was observed that the adaptive kernel technique yielded slightly higher hazard values in regions of high seismic activity and lower values in regions of low seismic activity. However both the techniques yielded similar results in regions of spatial uniform seismicity. A significant difference was observed in the uniform hazard spectra obtained for specific sites in south India when the bandwidth parameters were estimated considering whole of south India (regional) and an influence area of 300 km radius (local).

The use of foundations for support of retaining walls and earth fill embankments has increased in recent years to become a geotechnical solution for rapid construction of earth structures in soft ground conditions. With a growing number of successful case histories involving foundations in difficult ground conditions for various transportation applications, researchers have continued to investigate the behaviour and support mechanisms of the foundation elements. In the present work, different types of foundations are used to analyze behavior of reinforced earth retaining structures for 6m height of wall. Rammed Aggregate Pier (RAP), pile foundations and drilled shafts are used in this study. These foundation types can overcome space constraints. Analysis is carried out by using Finite Element program PLAXIS 2D. Wall deformations, settlement of ground behind the wall and facing panel deflections were compared for all three types of foundations used in the study. For drilled shaft, wall deformations, settlement of ground and facing panel deflections were found to be less compared to RAP and pile foundation.

This paper presents a meshfree modelling of two dimensional contaminant transport through saturated porous media using 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, two dimensional form of the advection-dispersion equation with continuous source is considered. The unknown concentration values are approximated by using moving least square approximants. 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. The results of the EFGM are compared with the analytical and finite element results and it is found that they match well.

This paper presents the results of two-way cyclic lateral load tests carried out on model pile groups embedded in soft marine clay. The tests are conducted on 1 × 2, 2 × 2 and 3 × 3 pile groups having length to diameter ratio (L/D) of 15, 30 and 40 with the spacing to diameter ratio (S/D) of 3, 5, 7 and 9. The experimental results are presented in the form of load-deflection curves and bending moment profiles. Cyclic group efficiency, critical spacing, critical cyclic load level and cyclic p-multipliers are evaluated. It is found that the lateral capacity of the 3 × 3 group reduces by about 42% after 50 cycles of loading. The cyclic p-multipliers of 3 × 3 pile group are found to be 0.41, 0.25 and 0.29 for leading, intermediate and rear rows respectively. The test results are compared with the numerical analysis carried out by p-y method using GROUP program. The analysis carried out with experimentally evaluated p-multipliers predicts load-deflection and bending profiles of pile groups reasonably well, but underestimates the depth to maximum bending moment by about 15%. © 2010 Springer Science+Business Media B.V.

Semi-active control of civil engineering structures has been widely implemented as they incorporate the inherent reliability of passive control systems and versatility to adapt as of active control systems. One such semi-active system is the usage of Magnetorheological (MR) damper in the control strategy. This paper presents the use of MR damper on a single degree of freedom (SDOF) system, modelled using the SIMULINK toolbox of MATLAB. The modified Bouc-Wen hysteretic model is used to model the MR damper. The developed SIMULINK model of the MR damper is validated with the experimental results available in the literature. A parametric study has been carried out to understand the effect of period on the response of the SDOF system with MR damper. In order to study the influence of uncertainties on system response, the fuzzy logic control algorithm is incorporated in the SDOF system with MR damper. It is found that the fuzzy controller reduces the voltage requirement of the MR damper by 80% as compared to that of the MR damper in passive on condition.

Site characterization involves taking samples of soil, testing the samples, and evaluation of subsurface features, subsurface material types and their properties. The accuracy of characterization depends on ground features, subsoil condition and changes in geological aspects. In order to get the geotechnical properties of the soil stratum, it is necessary to carry out experiments both in the laboratory and field. The laboratory and field tests produce information especially about the type and strength of soils which are vital for the economic and safe design of infrastructure facilities and buildings. In the Multi-channel Analysis of Surface Waves (MASW) test, concepts of refraction analysis, time term method and tomographic inversion are used to calculate the seismic wave velocity with respect to depth for full of temple complex. The shear wave velocities are generated for 2D profiles layer and classified the soil layer are made using the results of average shear wave velocity up to top 30 m of the overburden (Vs)30.

Among the various modes of failure of reinforced concrete (RC) cantilever retaining walls, the sliding mode of failure is invariably seen to be the critical mode governing the proportions of the wall. Traditionally, a constant factor of safety (usually 1.5) is adopted in the design of cantilever retaining walls against sliding and overturning instability, regardless of the actual uncertainties in the various design variables. This paper presents the stability analysis of cantilever retaining walls, accounting for uncertainties in the design variables in the framework of probability theory. The first order reliability method (FORM), second order reliability method (SORM) and Monte Carlo simulation (MCS) method are used as alternative ways to evaluate the probability of failure associated with the sliding failure of retaining walls of various heights (ranging from 4 to 8 m). Sensitivity analysis has shown that the angle of internal friction (Φ) and the coefficient of friction below the concrete base slab (μ) are the most sensitive random variables. It is shown that cantilever retaining walls, optimally proportioned to achieve a factor of safety of 1.5 against sliding failure, can have significant variations in the reliability index (or probability of failure). In order to achieve consistently a 'target' reliability index (β = 2.5 or 3.0), the factor of safety must be appropriately chosen, accounting for uncertainties, especially with regard to Φ and μ. In this paper, easy-to-use design tables have been developed for this purpose.

The effects of pile spacing, number of piles, and configuration on displacement and bending response of pile groups in clay under dynamic lateral loading were investigated. The displacement response of pile group in clay is strongly nonlinear. Pile-soil-pile interaction is predominant for the groups with closer spacing and with greater number of piles. Group interaction causes reduction in the group stiffness and increase in damping of the pile group. Strong group interaction leads to significant differences in bending profiles of different row piles of the groups. Dynamic lateral loading increases the maximum bending moment and active pile length. Copyright © A. S. Elnashai and N. N. Ambraseys.

Strength characteristics of loose to medium dense sand deposits improved by sand compaction piles (SCPs) are assessed by performing three-dimensional (3D) finite-element analysis using PLAXIS 3D. The Mohr-Coulomb model is employed to model the behavior of both sand and SCP. A laboratory test is performed on the SCP-treated sand deposit to validate the finite-element (FE) result and they are in good agreement. A parametric study is conducted on field-scale SCP FE models considering variations in the properties of sand deposit and geometrical parameters of the SCP on the pressure-settlement response. Based on the FE results, it is found that a nearly 21% increment in the ultimate bearing capacity of the SCP-treated sand deposit can be obtained when the diameter of the SCP is increased by 100 mm. Settlement improvement factors are estimated for the treated sand deposits at selected bearing pressures to understand the extent of improvement achieved.