True Three-Dimensional Geomechanical Model Tests for Stability Analysis of Surrounding Rock During the Excavation of a Deep Underground Laboratory

Abstract

Geological disposal at deep burial depths is a widely accepted method for the treatment of high-level radioactive waste, in which an underground laboratory is regarded as an essential facility to connect various aspects of the process. To evaluate the excavation-induced stability of the rock mass surrounding the underground laboratory for deep geological disposal of high-level radioactive waste in Beishan, Gansu Province, true three-dimensional geomechanical model tests are carried out for the first time. A model test loading system is developed with an intelligent numerical control function and automatic excavation apparatuses. The variations in the displacement and stress surrounding the caverns are revealed. The test results indicate that after excavation, (1) the surrounding rock deforms toward the cavern with small displacements less than 3 mm; (2) the radial stress is lower, and the tangential stress is higher; tensile stress is induced in certain parts near the intersection of caverns but at a magnitude lower than the tensile strength of the rock; (3) the excavation-induced perturbation reaches approximately 1.5–2.0 times the cave diameter; and (4) the surrounding rock shows stability after excavation due to the favorable geological conditions and the overall high strength of the surrounding rock. Nevertheless, enhanced support via combined bolting and shotcrete are recommended at the crossing sections. The research results verify the rationality of the design scheme and provide important guidance for the construction of underground laboratories for deep underground disposal of high-level radioactive waste.