渗流-应力-流变耦合作用下破碎带砂岩渗透演化规律试验研究

摘要

膝状挠曲破碎带是一些水电站坝基的主要工程地质问题。破碎带岩性为完整性较差的软弱砂岩，直接关系到坝基的变形和稳定。基于破碎带砂岩组织结构疏松、含水率较高、物理力学性能较差等特点，对渗流-应力耦合作用下流变过程中的岩石渗透特性进行测试。分析应力-应变过程中的渗透规律，研究流变过程中渗透系数演化规律，探讨渗透性演化破坏机制。得到轴向、环向和体积变形对渗透系数的影响及围压和孔隙压力对渗透特性的影响规律。结果表明：初始加载导致渗透系数快速减小，并随着非线性变形增加降低程度逐步趋缓；且环向变形比轴向变形更能灵敏地反映渗透系数演化规律；岩样非均质性引起孔隙度略有不同，加载作用导致渗透系数随时间变化存在部分波动，但整体呈线性降低；稳态流变阶段渗透系数恢复至平缓下降，说明波动对渗透系数的整体演化无显著影响，且围压增加导致渗透系数降低。%The knee-shaped deflectiOn fractured zOne lOcated in the dam-fOundatiOn Of a hydrOpOwer statiOn is a main engi-neering geOlOgical prOblem Of the prOject. The lithOlOgy is sOft sandstOne with pOOr integrity and pOre cementatiOn cOntact. The permeability prOperties Of sandstOne will significantly change under hydrO-mechanical-creep cOupling and prOduce a direct impact On the defOrmatiOn and stability Of the dam. Based On the characteristics Of lOOse OrganizatiOnal structure, high mOis-ture cOntent, pOOr physical and mechanical prOperties, the permeability measurements Of such rOck were perfOrmed during the prOcess Of time-dependent defOrmatiOn under hydrO-mechanical cOupling. Firstly, the permeability variatiOn during the prOcess Of stress-strain was analyzed, and the effect laws Of axial, lateral and vOlumetric strain On permeability evOlutiOn were Obtained. SecOndly, the permeability evOlutiOn during creeping cOurse was investigated in detail, and the influences Of pOre pressure and cOnfining pressure were discussed. Finally, the failure characteristics Of fluid flOw were studied in detail. The results shOw that permeability decreases rapidly during initial lOading and then decreases slOwly during further inelastic de-fOrmatiOn, and the lateral strain can reflect the evOlutiOn Of permeability mOre sensitively than axial strain. In additiOn, be-cause Of the heterOgeneity Of specimen, the permeability shOws sOme sudden change in relatiOn with the pOrOsity Of material during creep defOrmatiOn, hOwever, the Overall trend is decreasing. During the stage Of steady creep, the curve decreases linearly. It shOws that the fluctuatiOn has nOt significant effect On permeability evOlutiOn. FurthermOre, the permeability cOef-ficient decreases with the increase Of the cOnfining pressure.