High internal pressure induced fracture patterns in rock masses surrounding caverns: Experimental study using physical model tests

This research has experimented with artificial rock specimens that contain a circular or oblong hole using a novel physical modeling approach to investigate the failure behavior of rock masses surrounding a cavern with high internal pressure. The knowledge of fracture initiation and propagation in rock masses is crucial to the selection of underground storage construction sites and a stability evaluation method. Specifically, this research attempts to investigate the fracture initiation and propagation direction of the rock mass that encloses an underground gas/air storage cavern with high internal pressure under varying control conditions. The experiments are carried out with 200-time scaled-down artificial rock specimens under varying stress ratio (ki), overburden stress (σvi) and the joint's dip angle (α). The internal pressure applied to the hole is gradually increased until the fracture is initiated and propagates. Photogrammetric analysis is utilized to identify the rock mass response induced by increasing internal pressure and the occurrence of failure path. The experimental results indicate that the fracture initiation point and propagation direction of failure path are strongly influenced by the in-situ stress ratio, k. The findings also reveal that the site with an initial in-situ stress ratio greater than one is suitable for use as a high-internal-pressure underground cavern. In addition, in the presence of a nearby joint, the site with a smaller dip angle joint is more desirable. For the same in-situ stress ratio, an oblong-shaped cavern is more stable than a circular cavern (tunnel) of similar size, although both cavern configurations exhibit the similar failure patterns.