Based on stress dropping model

an elastoplastic-brittle model is established by using a softening threshold value to model the character of the geotechnical materials

twin shear strength theory and non-associated flow principle are used

and the large strain of softening zone is considered

a solution to cylindrical cavities expansion in elastoplastic-brittle materials is obtained. An example shows that the softening threshold value remarkably influences the deformations and range of the plastic zone; smaller threshold value leads greater expansion deformation

plastic zone range

and ratio of softening zone to entire plastic zone; and that considering the effects of intermediate principle stress on plastic yield or not

obviously influences the results.