Influence of shear stress on cylindrical cavity expansion in undrained elastic–perfectly plastic soil

Abstract

The conventional cavity expansion method is based on the assumption of uniform radial pressure applied at the cavity wall boundary without considering the shear stress. However, in practice, shear stress may exist at the cavity wall, such as during the drilling process of drilled displacement piles. This note presents an analysis of the influence of shear stress on cylindrical cavity expansion in an undrained elastic–perfectly plastic soil. The problem is formulated by assuming large strain in the plastic zone and small strain in the elastic zone around the cavity, with a plane-strain condition under the cavity expansion process. Plastic yielding is determined by the Tresca failure criterion and an associated flow rule. A closed-form solution for the pressure–expansion relation is given to modify the conventional pressure–expansion relation without considering the influence of the shear stress. The plastic zone radius, cavity wall limit pressure, stress and excess pore pressure are also obtained. Furthermore, parametric studies are carried out to investigate the influence of shear stress on the cavity wall limit pressure, stress, excess pores pressure distributions around an expanding cylindrical cavity and the plastic zone radius. The results show that shear stress at the cavity wall boundary has a significant influence on the pressure–expansion relation and cannot be neglected when deriving the cavity wall pressure or excess pore pressure. However, the plastic zone radius is not sensitive to the shear stress. The present work provides a more general solution and improves the conventional cavity expansion theoretical framework.