Analysis of Drained Cavity Unloading-Contraction Considering Different Degrees of Intermediate Principal Stress with Unified Strength Theory

Since previous studies give little consideration to the influence of different intermediate principal stresses in the cavity contraction problem, the unified strength theory (UST) is introduced into cylindrical cavity contraction. A closed-form unified equation for the large deformation of cavity contraction considering the influence of different degrees of the intermediate principal stress coefficientbis derived and verified by comparison with the existing solution based on the Mohr-Coulomb criterion. This analysis shows that consideration of intermediate principal stress can reduce cavity contraction, the essence of which is that introduction ofbleads to an increase in the critical yield pressure and makes elastoplastic (EP) boundary moving towards the cavity wall. Parametric analysis shows that the influence of the intermediate principal stress on the radial displacement of the cavity is not negligible while its influence on the radial stress can be neglected; the greater the intermediate principal stress coefficientbis, the smaller the plastic zone around the cavity; the effect of the intermediate principal stress cannot be ignored when the soil stiffness is small or the dilation angle is large, and vice versa. The proposed solution through introduction of large deformation and intermediate principal stress coefficientbquantifies the influence of the intermediate principal stress on the cavity unloading-contractions relationship and can model the cylindrical cavity contraction behavior in drained or "dry" soil conditions in elastic-perfectly plastic geomaterials.