Abstract: Natural rock mass usually contains multiple sets of cross-persistent joints, which greatly weakens its mechanical properties. This study aims to investigate the strength and failure characteristics of rock mass with two sets of cross-persistent joints. Under different confining pressures, compression tests are conducted at various inclination angles and spacing values of joints, respectively. Then obtained results are further stimulated by the elastoplastic numerical manifold method. The results show that the variation of strength with the joint inclination exhibits the multi-crest and multi-trough characteristics. The variation of strength with joint spacing confirms to a negative exponential function. According to the joint states, the failure modes of rock mass can be divided into three kinds, i.e., failure of rock block, slipping along a set of joints and slipping along two sets of joints. It is found that both sets of joints affected the strength of rock mass to certain degrees. Moreover, there is an interaction between these two sets of joints. Through the regression analysis of the simulation results, a new strength prediction model is established for rock mass with two sets of cross-persistent joints. The model is based on the strength prediction model of rock mass with one set of joints and the quantification of the interaction between two sets. The model is simple in form and easy to use, which can provide a guideline for evaluating the strength and failure characteristics of rock mass in practical engineering.

Key words: strength characteristic, failure mode, two sets of persistent joints, numerical manifold method, strength prediction model