Effects of Horizontal and Vertical Seismic Loads on the Bearing Capacity of a Surface Footing Adjacent to a Slope

Abstract

The correction factor (η ie ) for the ultimate bearing capacity of a footing placed adjacent to a slope, taking into account the combined effect of horizontal and vertical seismic loads, represented by horizontal and vertical seismic coefficients, k h and k v , respectively, was derived using a modified Janbu's slice method. The influence of slope angles ‘α’ on the values of ‘η ie ’ are studied here. It was found that the values of η ie can be expressed as an exponential function of ‘ k h /(1- k v )’ and ‘α’, with a measurable interdependency between ‘α’ and ‘η ie ’. The influence of ‘α’ on the value of ‘η ie ’ increases as the input value of ‘ k h /(1- k v )’ increases. Equations derived based on the analytical results are proposed to account for this effect. Based on the analyses of 11 near-fault seismographers obtained in the 1999 Chi-Chi earthquake in Taiwan, a ratio between the vertical and the horizontal seismic coefficients, λ, of between ±0.25 is suggested for including the combined effect of vertical and horizontal seismic forces in evaluating the seismic bearing capacity of footings located in near-fault areas.