Inversion Analysis of the 3D Geostress Field of Extremely Deep Underground Caverns with Fold Structure: A Study of the China Jinping Underground Laboratory

As the most deeply buried laboratory in the world, the China Jinping Underground Laboratory (CJPL) is characterized by high geostress with complex distribution due to the existence of anticline folds and faults as well as multistage historical tectonic processes. In this paper, a geostress inversion procedure for deep underground engineering with a fold structure is presented first, which includes in situ stress identification based on multisource information, the in situ stress numerical inversion and verification considering the measured data, and stress-induced failure characteristics of caverns. Then, the engineering design, geological conditions, geostress measured data, and failure characteristics of the CJPL are introduced. By applying the stress inversion process in the CJPL, the distribution characteristics of three-dimensional (3D) geostress along the fold structure are analyzed, and the mechanism of geostress distribution and rock mass stress-induced failure are studied. Finally, reasonable excavation and support suggestions of each cavern are proposed. The results indicate that the maximum principal stresses near the CJPL, influenced by the folds and lithology, vary from 60 to 70 MPa, with slight inclination and North-West (NW) strike. The stresses are disturbed significantly during cavern excavation, and the northern foot and southern spandrels of Labs 5#–8# is the stress concentration zone after excavation and suffers stress-induced failure. For the anticline fold, the stress decreases gradually from crest to limbs, with stress concentration at the core. Additionally, the lithology in the limbs is better than that at the core, which improves slightly the maximum principal stresses, and the displacement of surrounding rock of the fold core is larger than that of the fold limbs after cavern excavation. Reducing excavation footage, increasing stress release holes, sprinkling water, increasing prestressed anchors, and spraying steel fiber–RC are recommended for stress-induced failure prone areas of the CJPL.