Seismic bearing capacity factors for shallow foundations through different methods of analysis

Past earthquakes provided evidence of the susceptibility of shallow foundations to undergo large deformations and failure also in situations where liquefaction was not triggered. Several examples of these failures occurred after the 1971 San Fernando earthquake. the 1978 Miyagiken-Oki earthquake and the Michoacan earthquake that shook Mexico City in 1985. Experimental evidence of bearing capacity failures similar to those observed in the field was also provided by shaking table and centrifuge model tests on shallow foundations under dynamic excitation. In this study, the evaluation of earthquake-induced reduction of the bearing capacity is carried out for a shallow strip foundation using two different approaches, both relying on the application of the method of characteristics, extended to the seismic condition through the pseudo-static approach. Empirical equations, approximating the extensive numerical results, are given to compute corrective coefficients of static bearing capacity factors allowing to consider separately the effects of soil inertia and superstructure inertia. These equations can be introduced in current expressions of the bearing capacity to extend their applicability to seismic design of foundations