Failure Analysis on Surrounding Rock of Soft-Layered Rock Tunnel Using Coupled Continuum-Discrete Model

In order to study the failure mechanism of layered surrounding rock after tunnel excavation, taking the Zhegu mountain tunnel of Wenma highway as an example, a new numerical approach is put forward based on continuum-discrete coupling method. The failure patterns of surrounding rock under different geo-stress fields and bedding spacing are obtained through this method. The results show that: slipping and opening failure occurs on joint surface because of its low strength after stress redistribution during tunnel excavation. Then, stress field is disturbed furtherly and this disturbance leads to tensile failure of rock matrix; Micro-cracks in rock mass increases with the decrease of lateral pressure coefficient for the same stress level. When the lateral pressure coefficient is 1.00, 0.80, 0.67, 0.57, and 0.50, the total number of micro-cracks is 304, 391, 602, 999, and 1240, respectively. When the bedding spacing is 0.6 m, bedding has a controlling influence on the failure mode of surrounding rock, while this influence is weakened and the failure mode is similar to that of homogeneous surrounding rock with the increase of bedding spacing from 0.6 m to 1.2 m.