Investigation of failure behavior of continuous rock mass around cavern under high internal pressure

Abstract

A series of physical and numerical model tests were performed to investigate the failure behavior of a continuous rock mass surrounding a silo-shaped cavern under high internal pressure. This research aims to provide information on fracture initiation and propagation in the rock mass around an underground gas storage cavern occurring as a result of applying high internal pressure under different controlled conditions. By scaling down the prototype 200 times, synthetic rock specimens containing silo-shaped hole were confined to vertical pressures of 12.5 and 25kPa, with a Ko of 0.5, 1 and 3 in the two horizontal directions. The pressure was gradually applied in the silo until fracture initiated and propagated. The photogrammetric analysis provides insights into the response of the rock mass during the application of internal pressure and assists in identifying the failure path that occurred. The resulting fracture patterns indicate that the lateral earth pressure coefficient at rest, Ko, has a strong influence on the position of crack initiation and the propagation direction of the failure path. Supplemental numerical analyses were carried out to evaluate the failure mode, which cannot be addressed by the model tests. The numerical method, based on finite element method, considers stress analysis with localization and is developed to capture the formation of discrete fractures in a continuum. It is found that the method is able to accurately represent the factors that affect the fracture pattern and that a qualitative agreement between the experimental and numerical results can be established. A comparison between experimental and numerical results indicates that the fracturing process was caused by tensile cracking.