Abstract: Surrounding rock stability of underground caverns in the deep resources development are facing deformation and failure problems of post-peak fractured rock. The deformation and failure mechanisms of the deep fractured surrounding rock in strong unloading excavation are unclear, which normally leads to large volume collapse, large deformation and other major engineering accidents. In the current study, a large scale three-dimensional experimental model testing is conducted to investigate the characteristics of deformation and failure of deep rock mass with multi-cleftiness of different angles under the excavation condition at high in-situ stress. When the crack angle is small, the surrounding rock on upper and lower sides mainly presents large deformation phenomenon, and the rock on the left and right sides shows layered fracture phenomenon. With the increase of crack angle, the rupture zone from the left and right sides of tunnel gradually extends to the whole tunnel, and the top rocks become more prone to collapse. The displacement and stress of surrounding rock show the fluctuation from inside to outside. The plastic zone around the tunnel increases with the increase of crack angle. The larger the crack angle, the more the plastic zone around the tunnel is easily connected with the prefabricated crack at the top and bottom of the tunnel. The research provides some experimental data for ensuring the safety of construction and operation of deep underground engineering.

Key words: high in-situ stress, multi-cleftiness, layered fracture, model test