Deformation and Failure Characteristics of Three Sandstone Types Under True Triaxial Stress With a Fixed Lateral Stress Difference
This study conducts true triaxial compression tests on three types of sandstone under a constant intermediate principal stress of σ 2 = 28 MPa. The stresses applied to the X ‐direction surfaces are progressively increased while their difference remains fixed at Δ σ = 3 MPa. Strength, deformation, failure mode, energy evolution, and plastic strain increment ratios (PSIRs) are analyzed. The results show that increasing the X ‐direction boundary‐stress level enhances rock strength and deformation capacity, although the magnitude of enhancement varies with lithology. Weak sandstone is predominantly characterized by tensile splitting; medium sandstone gradually evolves toward mixed tensile‐shear failure, and strong sandstone exhibits the clearest transition toward shear‐dominated failure. Acoustic emission distribution and energy evolution analyses indicate that enhanced lateral constraint suppresses crack opening, promotes shear‐related cracking, and increases elastic strain energy storage. The PSIRs results show that the anisotropy of macroscopic lateral plastic deformation decreases as the X ‐direction boundary stresses approach σ 2 .