Influence of earthquake-induced pore water pressures on seismic bearing capacity of shallow foundations

Earthquake-induced excess pore water pressures may produce significant strength and stiffness degradation in foundation soils. Accordingly, severe loss in the bearing capacity of shallow foundations can occur possibly leading to extensive damage in the super-structures. Then there is the need of simple, but rigorous, solutions to account for the effect of earthquake-induced pore pressures on seismic bearing capacity of shallow foundations. This effect is examined in the paper using the method of characteristics. First the effect of hydrostatic pore pressures on bearing capacity was investigated providing a corrective coefficient to account for it; then the effect of seismic-induced excess pore pressures was considered in the analyses. A seismic bearing capacity factor accounting for both the soil and the superstructure inertial effects as well as for the effect due to the excess pore water pressure was proposed and formulas of corrective coefficients were also derived to be used in the conventional bearing capacity trinomial formula.