饱水作用对白砂岩损伤破裂及声发射特性的影响

Effect of Water Saturation on the Damage Failure and Acoustic Emission Characteristics of White Sandstone

含水软弱地层围岩的失稳破坏往往与水的作用密切相关。为深入揭示饱水作用对岩石损伤破坏的影响效应及力学机制,开展白砂岩在干燥及饱水条件下的单轴压缩试验,通过对比分析,研究饱水作用对其强度及变形、应力门槛值、应变能及声发射特性的影响规律及机制。分析结果表明,白砂岩饱水后:①单轴抗压强度、弹性模量降低,泊松比增大。②归一化起裂应力(σ_(ci)/σ_(f))减小。分析发现,水的软化作用削弱了矿物颗粒间的黏结作用,新生裂纹易于起裂,因而σ_(ci)/σ_(f)减小。③归一化损伤应力(σ_(cd)/σ_(f))减小。基于对声发射b值的分析,饱水后小尺度破裂比例增加,微裂纹更容易相互搭接并形成宏观破裂面,从而导致σ_(cd)/σ_(f)减小。④峰值强度处的总能量U、弹性能U_(e)和耗散能U d均减小,弹性能与总能量之比(U_(e)/U)下降。⑤基于声发射AF值(平均频率)及RA值(上升时间与振幅之比)分析发现,饱水后剪切破裂占比增大。研究结果对揭示饱水岩石的破坏机理具有一定的指导意义。

The instability and failure of surrounding rock in water-bearing weak strata are often closely related to the effects of water.To deeply reveal the influence and mechanical mechanism of water saturation on rock damage and failure,uniaxial compression tests on white sandstone under dry and water-saturated conditions were carried out.Through comparative analysis,the effects and mechanisms of water saturation on strength,deformation,stress thresholds,strain energy,and acoustic emission characteristics were studied.The results showed the following when the white sandstone was water-saturated:(1)Uniaxial compressive strength and elastic modulus decrease,while Poisson’s ratio increases.(2)The normalized crack initiation stress(σ_(ci)/σ_(f))decreases.The analysis shows that the softening effect of water weakens the bonding between mineral particles,making new cracks easier to initiate,thus leading to a decrease inσ_(ci)/σ_(f).(3)The normalized crack damage stress(σ_(cd)/σ_(f))decreases.Based on the analysis of the AE b-value,the proportion of small-scale ruptures increases.The increase in the proportion of small-scale fractures makes it easier for microcracks to coalesce into macrofractures,leading to a decrease inσ_(cd)/σ_(f).(4)The total energy(U),elastic energy(U_(e)),and dissipated energy(U d)at peak strength decrease,and the ratio of elastic energy to total energy(U_(e)/U)also decreases.(5)The analysis based on AE RA value(ratio of rise time to amplitude)and AF value(average frequency)shows that the proportion of shear fractures increases after water saturation,making it easier to produce intragranular fractures.The research results provide important insights into the failure mechanisms of water-saturated rocks.