Excavation damaged zone depths prediction for TBM-excavated roadways in deep collieries

The excavation works at underground mines create excavation damage zone (EDZ) in surrounding rocks around roadway geometry. The EDZ depth is a critical parameter for stability analysis, risk assessment support design and toxic waste leakage. This paper proposed an innovative EDZ depth prediction based on a modified nonlinear Mohr failure criterion and modification of conventional analytical solution by means of perturbation method. A set of cyclic loading tests of surrounding rock of roadways are conducted, and a modified Mohr failure criterion of rocks under cyclic loading path of TBM excavation is established on the basis of test results. Moreover, perturbation method was introduced for enhancing calculation accuracy. In order to verify the proposed analytical solution, a set of in situ digital panoramic borehole camera image monitoring was carried out within the roadways and the monitoring results correlated well with the proposed analytical solution. The EDZ geometries of roadways in deep mines are typically oval, and the EDZ depth is influenced by ground stress magnitude, lateral coefficient and support stress significantly. Through the proposed analytical solution, a more accurate prediction of EDZ depth of roadways can be obtained conveniently before the excavation works.