Effects of horizontal and vertical seismic loads on the bearing capacity of a surface footing adjacent to a slope

The correction factor (ζ_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 'ζ_ie' are studied here. It was found that the values of ζ_ie can be expressed as an exponential function of 'k_h/ (1 - k_v)' and 'α' with a measurable interdependency between 'α' and 'ζ_ie'. The influence of V on the value of 'ζ_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.