A Fracture Model for True Triaxial Compression Incorporating Pore Pressure Effect on Microcrack Surface in Brittle Rocks

Deep brittle rocks are subjected to true triaxial compressive stresses () coupled with pore fluid pressure. Existing models rarely distinguish the localized actions of pore pressure on different microcrack planes under true triaxial conditions. This study establishes a true triaxial micro–macro fracture constitutive model incorporating pore fluid pressure. At the microscale, the dual mechanisms of pore pressure, weakening effective normal stress on initial crack surfaces and inducing tensile driving forces on wing crack surfaces, are formulated, with cross‐scale damage evolution mapping microscopic crack propagation to macroscopic strain. At the macroscale, the lateral confinement effect of the intermediate principal stress () is incorporated into the hydromechanical constitutive equation. The model is validated against true triaxial seepage experimental data of yellow sandstone. Results demonstrate that pore fluid pressure degrades peak strength and accelerates unstable crack propagation, whereas effectively suppresses crack growth via lateral confinement.