Assessment on Bearing Capacity of Two Clay Layers Soil Using COMSOL

Abstract

Natural soils are often deposited in layers and homogeneous soils which are very rarely found in nature. Thus, bearing capacity of layered soil cannot be treated anymore as single soil since the soil strength and stiffness parameters are different and increase their linearly with depth. There are two cases which can be consider as inhomogeneous layer soil where strong clay overlaying weak clay layers or weak clay overlaying strong clay layers. A parametric study was conducted to assess the ultimate bearing capacity of a smooth strip footing subjected to vertical load resting on two undrained clays layered soil. A two dimensional (2D) plane strain model incorporated in COMSOL Multiphysics (version 4.3a) which a finite element software was adopted with two physical branches that have been chosen. Two clays layered soil were assumed as linear elastic incompressible material which failed in the Mohr-Coulomb criterion. The finite element results were presented in terms of a modified bearing capacity factor for different ratios of top layer thickness, strength and stiffness ratio of two clay layers. The computation results were then compared to published studies. The numerical analysis showed that strong clay overlaying weak clay layers with c1/c2 >1 resulted in increase of Nc* as h/B ratio increase. In contrast, for a case where weak clay overlaying strong clay layers with c1/c2 <1 showed decrease of Nc* as h/B ratio increase. In comparing results of bearing capacity factor, Nc* indicated a similar trend from previous studies. Stiffness parameters did not affect the solutions as long as remain constant for all cases within suitable ranges of parameters.