Coupled boundary element method for creep settlement of thick raft foundation on viscoelastic ground

A coupled boundary element method for analyzing the interactive behaviour between thick raft foundation and viscoelastic half-space soil medium below the foundation in the time domain is presented. The viscoelastic rheological model for soils, combining a standard Boltzmann model in deviatoric component with an elastic model in volumetric component, is employed, and the effect of transverse shear deformation in the raft foundation is considered as it bends under varying columnn loading during construction. The boundary element method is employed to simulate the raft foundation and the ground creep respectively, and the relevant numerical formulae are derived, in which the Newton quadratic interpolation for subgrade reaction in the time interval is introduced. The present method, as well as the computing pragrom, can be used to calculate settlements and differential settlements as well as bending moments and shear forces in the raft. It is shown that the values of subgrade reaction will slightly increase on the edges of the raft and decrease in the centric domain with soil creep after the completion of construction, but the values of variation are not significant and may be ignored reasonably. Howerver, the values of the raft settlement and differential settlement and the maximum bending moments increase pronouncedly with soil creep up to a few years, and tend towards their stable values. And thus the behaviors should be paid attention to in foundation designs for some soil strata with high rheology .