EFFECTS OF HORIZONTAL AND VERTICAL SEISMIC LOADS ON THE BEARING CAPACITY OF A SURFACE FOOTING ADJACENT TO A SLOPE

摘要

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.