高应力和高渗压下饱和完整砂岩三轴剪切-渗流耦合特性试验研究

Experimental study of triaxial shear−seepage coupling characteristics of saturated intact sandstone under high stress and high seepage pressure

为研究高地应力和高水头压力下完整岩石的三轴剪切力学特性和渗透特性,更加真实地揭示三维压剪应力状态下重大岩石边坡在剪切-渗流耦合作用下的损伤破坏机制,采用Rock Top多场耦合试验仪,对饱和完整砂岩进行五组不同法向应力和渗压下的三轴剪切-渗流耦合试验,获得相应的三轴剪应力-应变-表观渗透率曲线和含有原岩屑的剪切单节理裂隙面,并开展单节理裂隙渗透试验。分析不同法向应力和渗压双因素耦合作用下岩石剪切破坏裂隙面的形貌特征,探究饱和砂岩的剪切强度和表观渗透率随法向应力、渗压的演变规律,探讨单裂隙砂岩的表观渗透率在剪应力逐渐减小过程中随渗压的演化特征。研究结果表明:1)剪切-渗流耦合作用下饱和砂岩表观渗透率表现出先减小后增大并逐渐趋于稳定的变化规律;2)剪切-渗流耦合下饱和砂岩剪切峰值强度和残余强度随着法向应力增大而增大,随着渗压的增大呈线性减小,并且在剪切过程中表观渗透率曲线渗流峰值滞后于剪切峰值强度;3)在剪应力缓慢降低过程中,单节理裂隙面的开度先降低后增大,其表观渗透率和渗流量呈现出先减小后增大的变化规律;4)采用Forchheimer方程拟合获得剪应力、渗压和法向应力作用下,贯穿单裂隙面的渗流量与渗压的关系式。

To study the shear mechanical characteristics and permeability characteristics of intact rock in high shear stress-seepage pressure coupling,the damage and failure mechanism of large rock slope in shear-seepage coupling in three-dimensional compressive shear stress state was revealed more truly,five triaxial shear-seepage coupling tests at different normal stress and seepage pressures were carried out by Rock Top multi-field coupling apparatus for intact saturated sandstone,and then the corresponding triaxial shear stress-strain-apparent permeability curves and five single-joint fractures containing native rock piece were obtained applied to seepage tests.The morphological characteristics of rock shear failure fracture surface during the coupling of different normal stress and seepage water pressure were analyzed.The variation of shear strength and apparent permeability of saturated sandstone with normal stress and seepage pressure were explored.At the last,the evolution characteristics of the apparent permeability of the single-fracture sandstone with the seepage pressure in the decrease of the shear stress were discussed.The results show that the permeability of saturated sandstone decreases first and then increases,and finally tends to be stable under shear-seepage coupling condition.In the shear seepage coupling,the peak shear strength and residual strength of saturated sandstone increase with the increase of normal stress and decrease linearly with the increase of seepage pressure.The peak permeability lags behind shear strength value in the whole shear-seepage process.In the process of slowly decreasing shear stress,the aperture of the single fracture surface decreases first and then increases,and its apparent permeability and flow rate show a change law that first decreases and then increases.The relationship between the seepage flow and seepage pressure of the penetrate single fracture surface under shear stress,seepage pressure and normal stress is obtained by Forchheimer equation fitting.