Effect of strength criteria on surrounding rock of circular roadway considering strain softening and dilatancy

In order to study the effect of strength criteria on the surrounding rock stability of circular roadway,under the plane strain condition,a unified yield equation was firstly summarized for four commonly used strength criteria of rock materials,such as Mohr-Coulomb ( MC) criterion,Drucker-Prager ( DP) criterion,uniform strength theory and Mogi-Coulomb (MO) criterion. Then,the circular roadway surrounding rock was divided into fracture zone,plastic sof- tening zone and elastic zone,and the softening modulus of strength parameters and coefficients of dilatancy were intro- duced by considering the intermediate principal stress effect,post-peak strain softening and dilatancy. Furthermore,the new unified solutions for stress,displacement and plastic zone radius of surrounding rock had been deduced,and the comparative analyses were conducted on the various influence factors of the new solutions. It was found that the new solutions proposed in this paper not only have the form of conciseness, but also can flexibly match different rock strength criteria. The strength criteria without considering the effect of the intermediate principal stress are relatively conservative. When considering the effect of intermediate principal stress,the radius and displacement of the plastic zone calculated by the MO criterion and the unified strength theory with weight coefficient less than 0. 5 are in the middle level. The circumcircle DP criterion and the unified strength theory with weight coefficient greater than 0. 5 have more considerations for the effect of the intermediate principal stress,which should be selected carefully. The strain softening causes the properties of the surrounding rock in the plastic zone to be further degraded,resulting in a wider range of fracture zone. Increasing the residual strength of the fracture zone is an effective support method. The di- latancy is not only related to the dilatancy angle,but also related to the plastic potential function,in addition,the actual deformation of surrounding rock will be underestimated without the consideration of dilatancy. The results can provide an important theoretical basis for roadway surrounding rock’s stability evaluation and quantitative support design.