Impact of fracture networks on the structural deformation of lined rock caverns under high internal gas pressure

In this paper, we develop a two-dimensional (2D) numerical model based on the finite element method to analyse the impact of fracture networks on the behaviour of pressurised lined rock caverns (LRCs). We use the discrete fracture network approach to represent the fracture system in rock obeying a power law length distribution. The LRC consisting of an inner steel lining and an outer reinforced concrete is situated within the rock mass characterised by spatially distributed and intersected fractures. An elasto-brittle constitutive relationship is adopted to characterise the deformation/failure of intact rocks, while the classical Mazars damage model is used to simulate the cracking of concrete linings. For pre-existing fractures in rock, a non-linear stress-displacement formulation is implemented to capture their normal and shear deformations. The 2D model, representing the horizontal cross-section of an LRC with its surrounding rock mass, is subject to a prescribed in situ stress condition. We explore various fracture network scenarios associated with different values of power law length exponent and fracture intensity. We analyse the damage evolution in rock/concrete and tangential strain in the concrete/steel linings. It is found that the damage within the rock mass mainly evolves in the form of wing cracks that emanate from the tips of pre-existing fractures. For damage development in the concrete lining, it is primarily induced by tensile cracking under cavern pressurisation. The damage emerges in the lining sections where pre-existing fractures are located in the tensile region around the cavern and either intersect with the cavern wall or could reach the cavern wall by promoting wing crack propagation. The results and insights obtained from our study have significant implications for the design optimisation and performance assessment of LRCs for sustainable hydrogen storage.