CYLINDRICAL CAVITY EXPANSION AND CONTRACTION IN PRESSURE-SENSITIVE GEOMATERIALS

A broad class of plane-strain axially-symmetric deformation patterns i n geomaterials is studied within the framework of large strain pressur e-sensitive plasticity. Invariant, non-associated deformation-type the ories are formulated for the Mohr-Coulomb (M-C) and Drucker-Prager (D- P) solids with arbitrary hardening and accounting for an initial hydro static state of stress. With the M-C model we arrive at a single first order differential equation, while for the D-P solid an algebraic con straint supplements the governing differential equation. The analysis centers on the effective stress as the independent variable. A simplif ied treatment is given for the cavitation Limit and some useful relati ons are derived for thin walled cylinders. The theory is applied to th e triaxial calibration test for Castlegate sandstone and then used to simulate the hole closure problem. Numerical examples are provided for the case of a cavity embedded in an infinite medium subjected to exte rnal or internal pressure. Results for the D-P inner cone model were f ound to be in dose agreement with those obtained from the M-C model.