An analytical micro-macro model of creep fracture driven by cyclic pore pressure in brittle rocks

Cyclic pore pressure is closely related to the stability and safety of deep underground engineering. A micro-macro mechanical model of creep fracture under cyclic pore pressure, external confining pressure, and axial stress was established to reveal the mechanism of cyclic pore pressure of brittle rock. The model combines the improved microcrack model, the function of cyclic pore pressure, the subcritical crack law, the Hooke-Kelvin model, and the crack-strain model. The complete elastic, viscoelastic and plastic deformation of rock is described. The model solution before crack extension determines the elastic and viscoelastic deformation, and that of after crack extension determines the plastic deformation. Time-dependent elastic modulus evolution of rock under cyclic pore pressure is obtained, which affects viscoelastic strain under cyclic pore pressure. The effects of cyclic pore pressure parameters Δ P and Δ P and cycle period on rock viscoelastic rebound value and creep fracture time are discussed. Rationality of the proposed model is verified by experimental data. The analytical results provide help for evaluation in safety and stability of rock engineering.