Bearing Capacity and Plastic Flow of a Rate-Sensitive Clay under Strip Loading

Abstract

The behavior of a rate-sensitive, saturated clay under strip loading is analysed using the method of finite elements. Emphasis is placed on assessing time effects upon the bearing capacity of such a clay foundation. Computationally, this is made possible by implementing a viscoplastic constitutive model into the analysis procedure and by performing coupled stress-flow analyses with due consideration of the two-phase nature of saturated clay. Loading tests with constant rates of loading as well as those under sustained loads, are treated. It is found that the undrained bearing-capacity factor, N_c, is practically independent of the loading rate despite the significant rate-sensitivities of the bearing capacity and shear strength themselves. It is also found that, within the undrained clay mass undergoing creep under constant loads, there occurs a continued reduction in shear stress with time, and that this stress redistribution prolongs the moment of possible failure under sustained loading much more, as compared with the fictitious situation where the shear stress would remain unchanged. Furthermore, it is shown that partial consolidation during the loading stage exerts profound effects on the migration of effective stress state and on the mobilization of bearing capacity with foundation settlement.