Mechanisms of failure for shallow foundations under earthquake loading

It is widely known that the bearing capacity of a shallow foundation is reduced when the foundation is subjected to rocking moments and horizontal loads during an earthquake event. Analytical solutions generally require an assumption to be made of the kinematic failure mechanism in the soil, when the true failure mechanism is unknown. This paper discusses a series of experiments carried out on a new 1g shaking table at Cambridge University in order to measure the displacements of a shallow foundation due to seismic loading and also the development of the failure mechanism within the soil. The failure mechanism was studied using the technique of Particle Image Velocimetry (PIV), combined with high-speed videography and photogrammetry. In this paper, the failure mechanisms observed in these experiments will be compared with the theoretical results found from upper- and lower-bound solutions and the effects of such parameters as earthquake magnitude, frequency and embedment ratio (and hence surcharge) will be discussed.