Surrounding Rock Failure Mechanism and Long-Term Stability of the Heidong Large Ancient Underground Caverns

The Heidong ancient man-made underground caverns consist of 21 single caverns and the group caverns cover an area of 24,000 m(2). The large-scale underground quarry with 21 caverns has been preserved in its original state for more than 1400 years in Tiantai County of South China due to the favorable engineering geological conditions and the structural integrity of rock mass. In this study, based on the field investigation method and numerical simulation, the deformation and damage of the surrounding rock of each ancient cavern chamber were studied, and the damage types and damage mechanisms of the surrounding rock were analyzed. The influence on the long-term stability of the cavern was analyzed in terms of ancient engineering concepts and the quality of the surrounding rock. Research results showed that cavern block instability has caused some roof collapse due to gravity and the horizontal displacement conditions. The higher quality of the surrounding rock in layers 6 and 8 is an important reason for the long-term stability of the ancient caverns. In addition, the ancient engineering idea implemented, including double-arched structure and fault avoidance, as well as waste rock accumulation on the floor of the caverns, have played an important role in their long-term stability. Overall, this study is relevant to modern underground engineering seeking to promote the scientific protection for ancient engineering constructions.