Abstract:

As the internal pressure gradually increases, the surrounding rock of a tunnel-type hard rock gas storage cavern will undergo three phases: fracture initiation at the cavern wall, fracture propagation, and eventual cavern failure. Fracture initiation occurs due to shear or tensile failure of the surrounding rock at the cavern wall, and is governed by the rock mass’s shear strength and tensile strength. We employed FLAC2D numerical analysis based on the Mohr-Coulomb criterion to locate fracture initiation points on the cavern wall and the associated initiation pressure, accounting for the initial stress field. Boundary effects become negligible when the lateral boundary spacing is at least 15D and the bottom boundary spacing is at least 10D (where D is cavern diameter). The lateral pressure coefficient k and cavern burial depth H significantly influence the fracture initiation angle α, the characteristic curves of fracture initiation angles exhibit two distinct patterns: exponential curve type and horizontal straight-line type; the fracture initiation pressure P₀ is markedly affected by multiple factors including the lateral pressure coefficient k, burial depth H, shear strength (c, φ)and tensile strength R_t, the characteristic curves of fracture initiation pressure display a piecewise-linear pattern. Using elastic theory analytical methods, this paper derives analytical calculation formulas for both fracture initiation pressure and angle. The analytical solutions for fracture initiation pressure show good agreement with the numerical results. However, because finite boundary conditions of overlying rock mass, the analytical solutions for fracture initiation angle demonstrate some discrepancies with numerical results for k in the range 0.95–1.2.

Key words: compressed air energy storage, tunnel-type gas storage cavern, fracture initiation angle, fracture initiation pressure, characteristic curve