Elastoplastic solution of drained expansion of a cylindrical cavity in structured soils considering structure degradation

Abstract

An elastoplastic solution of drained cylindrical cavity expansion is presented based on a well-known critical state model for soils exhibiting a natural structure. The model referred to as the structured Cam-clay (SCC) model is capable of describing the properties of the soil structure and its subsequent stress-induced degradation. The asymmetric stiffness matrix of the elastoplastic constitutive equation for structured soils is derived due to the assumption of the non-associated plastic flow rule. The solution procedure is formulated by transforming the boundary value problem of cylindrical cavity expansion into the problem of solving four ordinary differential equations with three stress components and the specific volume as the basic unknown variables. The theoretical solution is numerically calculated and validated against the existing solution and finite element simulation results. Furthermore, the significance of the soil structure and its stress-induced degradation in the expansion response, and the interaction between the soil structure and overconsolidation are emphasized by extensive parametric analyses. The results demonstrate that the soil structure has a substantial influence on the cavity expansion response, and its degradation is closely related to overconsolidation. Particularly, among the solutions considered, the solution considering the soil structure provides higher effective stress values near the cavity surface due to the additional strength conveyed by the natural structure.