Gas-mechanical coupled crack initiation analysis for local air-leakage of compressed air energy storage (CAES) cavern with consideration of seepage effect

Abstract

The gas-tightness and stability of compressed air energy storage (CAES) cavern (usually with three-layered struction of sealing layer, concrete lining and surrounding rock) plays an important role for ensuring the power-generation efficiency of CAES system. Since the action of the compressed air with high temperature and high pressure would possibly cause the local damage of the sealing layer and lead to the air-leakage from the sealing layer to the surrounding rock, it is necassary to study the gas-mechanical (GM) coupled crack initiation behavior of the surrounding rock in order to provide a scientific basis for anti-cracking design and stability evaluation of CAES cavern. Currently, the GM coupled crack initiation are studied mainly by experimental and numerical methods but little by theoretical method, in which the gas pressure is taken as a static pressure regardless of the seepage effect. In this paper, the calculation formulea of GM coupled Mode I and Mode II SIFs are derived by the superposition principle with the consideration of seepage effect firstly. And then the criterion of GM coupled crack initiation is established based on our K-ratio criterion in order to analyze its mechanism for local air-leakage of CAES cavern. Finally, a gas seepage device is designed to conduct the tri-axial GM coupled compression tests of pre-cracked sandstone specimens on MTS815 hydraulic servo testing machine combined with PCI-II AE instrument to measure the crack initiation stress σi and initiation angle θC. Research results show both σi and θC are decreased with the increasing of gas pressure PG, while increased with the increasing of crack inclination angle β. All of these pre-cracked sandstone specimens have initiation mechanisms of Mode II. The prediction results of initiation angle with consideration of seepage effect is more closer to the test results than those of initiation angle without consideration of seepage effect, which can prove the validity of both our SIFs calculation formulea and the GM coupled criterion with consideration of seepage effect.