Cylindrical cavity expansion responses in anisotropic unsaturated soils under plane stress condition

In this paper, an anisotropic critical state model for saturated soils was extended to unsaturated conditions by introducing suction into its yield function. Combining this model with soil-water characteristic curves related to porosity ratio was employed to characterize the coupled hydromechanical behavior of unsaturated anisotropic soil. Based on the plane stress condition, the problem of the cylindrical cavity expansion in unsaturated anisotropic soils was transformed into first-order differential equations using the Lagrangian description. The equations were solved as an initial value problem using the Runge-Kutta algorithm, which can reflect the soil-water retention behavior during cavity expansion. Parametric analyses were conducted to investigate the influences of overconsolidation ratio (OCR), suction, and degree of saturation on the expansion responses of a cylindrical cavity in unsaturated anisotropic soil under plane stress condition. The results show that the above factors have obvious influences on the cavity responses, and the plane strain solution tends to overestimate expansion pressure and degree of saturation but underestimates suction around the cavity compared to the proposed plane stress solution. The theoretical model proposed in this paper provides a reasonable and effective method for simulating pile installation and soil pressure gauge tests near the ground surface of the unsaturated soils.