Damage evolution mechanism and energy response of sandstone under triaxial compression

This study investigates the mechanical behavior, damage evolution, and energy response of sandstone under high confining stresses, a critical issue in deep underground engineering. A series of triaxial compression tests were conducted on sandstone specimens under confining stresses of 3, 6, 9, 12, and 15 MPa to systematically analyze the influence of confining stress on the complete stress-strain response and the associated energy evolution. Based on the experimental results, a statistical damage constitutive model incorporating energy dissipation was developed, in which the failure probability of microscopic elements is described by the Weibull distribution and damage evolution is driven by energy dissipation. The results show that increasing confining stress significantly enhances both peak and residual strength: as confining stress increases from 3 MPa to 15 MPa, peak strength increases by 78% (from 43.365 MPa to 77.191 MPa) and residual strength increases by 196% (from 16.301 MPa to 48.241 MPa), while the failure mode transitions from brittle to ductile behavior. Energy analysis reveals that the deformation and failure process is governed by energy accumulation and dissipation; the pre-peak stage is dominated by elastic energy accumulation, whereas the post-peak stage is characterized by a sharp increase in dissipated energy. Elevated confining stress substantially enhances the energy storage limit, which at 15 MPa reaches 0.3322 MJ/m3—58.4% higher than at 3 MPa. The established constitutive model accurately captures the full-stage mechanical behavior from compaction and elasticity to yielding and residual strength, with theoretical curves showing good agreement with experimental data. Model parameters m, F0, and q exhibit clear physical meanings, reflecting strength, brittleness, and residual strength characteristics, respectively. Furthermore, an energy catastrophe criterion for instability failure is proposed. Analysis based on this criterion shows that as confining stress increases from 3 MPa to 15 MPa, the damage energy release rate Yc increases by over 120% (from 0.043 to 0.096), and the failure intensity index FId rises from 3.76 to 5.40, indicating a stronger tendency toward dynamic catastrophe under high confining stresses. This study clarifies the controlling role of confining stress on the mechanical behavior, energy evolution, and failure mode of sandstone, providing quantitative indicators and a theoretical basis for stability analysis and hazard prevention in deep engineering rock masses.