EARTHQUAKE INDUCED SHALLOW FOUNDATION SETTLEMENTS

Abstract

From the geographical statistics of India, it is seen that major portion of the Indian land is vulnerable to earthquakes. During an earthquake, shaking is triggered by the seismic waves, which causes damage or collapse to the buildings. The seismic loads and moments, which are imposed on the foundation by an earthquake results in additional settlements of the foundation. In this study, analyses are carried out to evaluate the settlements of footings subjected to seismic loading. The main objective of this work is to evaluate the settlements of footings resting on plane and sloping grounds using non-linear constitutive laws of soil. Pseudo-static analysis is used for the evaluation of the dynamic forces. The constitutive laws define the mechanical behavior of the soil considered. The strength and the non-linear stress-strain characteristics are taken into consideration using this. For the analysis of settlements, the soil layer is considered to a depth equivalent to five times the width of the footing (5B). This soil layer is further divided into smaller layers for evaluating the stresses in each layers. These stresses are further used to obtain the strain values and thus the settlements are calculated. Different parameters, such as the depth to width (D/B) ratio of the foundation, horizontal and vertical seismic coefficient (Ah and Av), stiffness and strength of the soil (hyperbolic constants -1/a and 1/b) and height of point of application of the horizontal seismic forces from the base of the footing (h) are considered. In addition, for the sloping ground, slope parameters like different slope inclinations (ꞵ˚) and also the setback distances from the edge of the slope to the footing edge (B’) are considered. Finally, conclusions are drawn, giving the seismic settlements and bearing capacity of the soil with respect to the various parametric studies carried out. It is observed that the footings that are located below the ground level have lower values of settlement for a given pressure intensity. Also, as the hyperbolic values increases it indicates better soil and therefore the settlement values decreases. Results show that, with increased slope inclination and decreased set-back distances from the slope edge, the settlements increases in a non-linear trend.