Seismic bearing capacity and settlements of shallow foundations

The safety factor of shallow foundations under seismic loading may drop many times and for short periods to values below unity. This temporary loss of stability can lead to sliding movements of the soil wedge under the footing when the critical acceleration is exceeded in either direction. In this paper, the methods for calculating the bearing capacity degradation and the entity of the settlements associated with the soil wedge sliding are compared and discussed. Reference is made to Italian seismic zones and to the reduction of bearing-capacity factors expected in these areas. In addition, while assuming the kinematic model of Richards et al.(1993), some empirical relationships which link the displacements of Newmark’s rigid block model along an horizontal plane and some of the more significant synthetic parameters of ground motion as far as Italy is concerned, are discussed