Large-scale geo-mechanical model tests for the stability assessment of deep underground complex under true-triaxial stress

Abstract To ensure the stability of a deep underground complex during its construction and operation, it is important to understand its deformation and failure behaviors before its construction. In this study, taking China’s first underground research laboratory (URL) for the geological disposal of high-level radioactive waste (HLW) in Beishan area as engineering background, we carried out large-scale three-dimensional (3D) geo-mechanical model tests on a deep underground complex consisting of a shaft and three intersecting tunnels. Based on the self-developed 3D loading system, the miniature excavating apparatus and the analogous material, the stability of the underground complex during its excavation and under overloading are systematically evaluated. The test results effectively reveal the deformation and failure behaviors of the underground complex. The interactions between adjacent excavations are elucidated. The overloading safety factors are obtained from the overloading test: the safety factor of crack initiation is between 1.5 and 2.0; the safety factor of local failure is between 2.0 and 2.5; and the safety factor of overall failure is between 2.5 and 3.0. The test results provide important guidance for the stability evaluation of the URL in construction and operation. These results also provide an ideal data set for the calibration and validation of numerical models to simulate the deformation and failure of underground structures.