陷落柱骨架砂岩三轴压缩渗流特性及声发射特征试验研究

Research on permeability and acoustic emission characteristics of karst collapsed column skeleton sandstone under triaxial compression

为研究陷落柱骨架砂岩在不同围压及渗透压条件下的力学性质、渗流特性和声发射基本特征,采用岩石三轴渗流实验系统及AE21C声发射监测系统,开展三轴压缩条件下渗流试验,得到砂岩变形过程全应力-应变及渗透率演化曲线,同时获得砂岩变形、渗透率及声发射信号演化规律。研究结果表明:(1)陷落柱骨架砂岩具有明显的脆性特征。渗透压相同时,砂岩应力峰值强度、弹性模量及峰值应变随着围压的增大而增大;围压对砂岩宏观破坏特征影响明显,破坏形式由多裂纹剪切破坏逐渐变为单斜面剪切破坏。(2)砂岩总体呈现低渗透特性。砂岩渗透率演化规律与三轴加载应力-应变关系具有密切的相关性。渗透率总体呈现出逐渐减小,平稳发展,迅速增加的三阶段变化特征。(3)声发射变化特征与应力-应变及渗透率曲线特征基本一致。初期阶段,振铃计数率随围压升高而减小;裂隙发育扩展阶段,声发射振铃计数率呈现密集活跃状态并逐渐增大;失稳破坏阶段,振铃计数率迅速增大后又快速回落。试验结果对于研究岩溶陷落柱的稳定性及渗透性变化规律具有重要参考价值。

To study the mechanical properties,seepage characteristics and essential acoustic emission characteristics of collapse column skeleton sandstone under different confining pressures and osmotic pressures,triaxial compression seepage tests were conducted by triaxial seepage experiment system combined with AE21C acoustic emission monitoring system,and the total stress-strain curve and the permeability curve of sandstone during deformation,as well as the evolution laws of deformation,permeability and acoustic emission signals of sandstone,were obtained.The results show that collapse column skeleton sandstone has obvious brittleness,that under the same osmotic pressure,the peak stress strength,the elastic modulus and the peak strain of sandstone increase with increasing the confining pressure,and that the confining pressure has an apparent effect on the macroscopic failure characteristics of sandstone with the failure mode gradually changing from multi-crack shear failure to single inclined-plane shear failure.The sandstone has low permeability characteristics,and the evolution law on the permeability of sandstone,generally characterized by a three-stage evolution of gradual decrease followed by steady development and rapid increase,is closely related to the stress-strain relationship under triaxial loading.It is also revealed that the variation characteristics of acoustic emissions are essentially consistent with the characteristics of stress-strain and permeability curves.In the initial stage,the ringing counting rate decreases with increasing the confining pressure;in the fracture development and propagation stage,the ringing counting rate of acoustic emissions presents a densely active state and gradually increases;during the unstable failure stage,the ringing counting rate increases rapidly and then quickly decreases.The test results provide an essential reference for studying the variation laws of a karst collapse column's stability and permeability.