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<p>Sandstone in deep water-bearing strata is a key geological medium in water-rich underground engineering, where hydro–mechanical (H–M) coupling strongly influences its strength, permeability, and failure behavior. To clarify the mechanical response and instability mechanism of sandstone under H–M coupling, a series of triaxial seepage-coupled tests were conducted under different confining pressures and seepage pressures (0, 1, 3, and 5&#xa0;MPa). The results show that increasing seepage pressure significantly reduces the peak strength and elastic modulus, promotes crack initiation, propagation, and coalescence, and lowers the characteristic stress thresholds, whereas higher confining pressure suppresses crack dilation and enhances overall stability. Cohesion decreases with seepage pressure following a power-law trend, while the internal friction angle declines approximately linearly, indicating progressive weakening of intergranular friction and cementation. Permeability evolution exhibits a staged response associated with pore compaction, crack propagation, fracture connectivity, and post-peak flow persistence. As seepage pressure increases from 1 to 5&#xa0;MPa, the maximum permeability increases by about 69.6%, whereas increasing confining pressure from 6 to 14&#xa0;MPa reduces it by about 48.5%, revealing a competitive mechanism between seepage-induced enhancement and confinement-induced suppression. Energy evolution is characterized by accumulation, damage propagation, and abrupt release, and both peak strain energy and damage strain energy decrease exponentially with increasing seepage pressure, indicating reduced energy storage capacity and accelerated failure. Macroscopic failure is dominated by oblique shear, with the fracture angle decreasing from 67.9° to 64.1° as seepage pressure increases. At the pore scale, the sandstone evolves through micropore depletion, mesopore-dominated reconfiguration, and macropore expansion and stabilization, with mesopores (0.1–10&#xa0;μm) representing a key pore-size range in pore-system reorganization, whereas macropores may be more directly linked to the formation of highly connected seepage pathways associated with permeability enhancement. These results provide a refined understanding of the coupled effects of seepage pressure and confining pressure on sandstone degradation and offer a mechanistic basis for stability evaluation in water-rich underground engineering.</p>

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Experimental Study on Mechanical Behavior, Permeability Evolution, and Failure Mechanism of Sandstone Under Hydro–Mechanical Coupling

  • 期刊论文

  • 发表日期：

    2026年7月29日

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  • Bowen Cheng,
  • Yuliang Zhang,
  • Zheyuan Feng,
  • Xinping Li,
  • Mingxu Li,
  • Guoyan Luo

摘要

Sandstone in deep water-bearing strata is a key geological medium in water-rich underground engineering, where hydro–mechanical (H–M) coupling strongly influences its strength, permeability, and failure behavior. To clarify the mechanical response and instability mechanism of sandstone under H–M coupling, a series of triaxial seepage-coupled tests were conducted under different confining pressures and seepage pressures (0, 1, 3, and 5 MPa). The results show that increasing seepage pressure significantly reduces the peak strength and elastic modulus, promotes crack initiation, propagation, and coalescence, and lowers the characteristic stress thresholds, whereas higher confining pressure suppresses crack dilation and enhances overall stability. Cohesion decreases with seepage pressure following a power-law trend, while the internal friction angle declines approximately linearly, indicating progressive weakening of intergranular friction and cementation. Permeability evolution exhibits a staged response associated with pore compaction, crack propagation, fracture connectivity, and post-peak flow persistence. As seepage pressure increases from 1 to 5 MPa, the maximum permeability increases by about 69.6%, whereas increasing confining pressure from 6 to 14 MPa reduces it by about 48.5%, revealing a competitive mechanism between seepage-induced enhancement and confinement-induced suppression. Energy evolution is characterized by accumulation, damage propagation, and abrupt release, and both peak strain energy and damage strain energy decrease exponentially with increasing seepage pressure, indicating reduced energy storage capacity and accelerated failure. Macroscopic failure is dominated by oblique shear, with the fracture angle decreasing from 67.9° to 64.1° as seepage pressure increases. At the pore scale, the sandstone evolves through micropore depletion, mesopore-dominated reconfiguration, and macropore expansion and stabilization, with mesopores (0.1–10 μm) representing a key pore-size range in pore-system reorganization, whereas macropores may be more directly linked to the formation of highly connected seepage pathways associated with permeability enhancement. These results provide a refined understanding of the coupled effects of seepage pressure and confining pressure on sandstone degradation and offer a mechanistic basis for stability evaluation in water-rich underground engineering.