Seismic bearing capacity of shallow strip footing resting on two layered sands

The objective of this article is to estimate quantitatively the improvement in pseudostatic bearing capacity of a rough strip footing by inclusion of a dense sand layer between the footing and the existing loose sand. The analysis is being performed by using lower and upper bound limit analysis in conjunction with finite elements and nonlinear optimization. The results are presented in the form of an efficiency factor (eta). The solutions are obtained for different combinations of horizontal and vertical seismic acceleration corresponding to varying strength ratios and dense (top) layer thickness. From the analysis, it is observed that the value of eta increases significantly with the overlaying of dense sand layer. However, there is a certain optimum thickness of the dense sand layer beyond which there is no further increment. The effects of the seismic coefficients and the shear strength of sand layers on the optimum thickness are established.