单轴压缩声发射试验的页岩损伤演化规律

Evolution of Shale Damage in Uniaxial Compression Acoustic Emission Tests

为获得受载页岩准确的损伤演化规律和声发射特征,完善以往受载岩石损伤单调增大的理论,进一步扩展对受载岩石内部损伤演化机理的认识,对陆相页岩进行单轴压缩声发射试验。试验结果表明:页岩单轴压缩过程分为4个阶段:压密阶段-弹性变形阶段-弹塑性变形阶段-峰后破坏阶段,压密阶段、弹性变形阶段和弹塑性变形前期有少量声发射信号,页岩峰值应力前后有大量声发射信号,特别是峰后破坏阶段,声发射信号急剧上升,声发射探头能够捕捉岩石的压密、裂纹的扩展和连通信息,声发射信号能够反映页岩内部微细观损伤演化过程;页岩平行层理面方向和垂直层理面方向的岩石损伤演化和声发射特征差别较大,因此对于层理性岩石不能忽略层理对岩石力学性质的影响;页岩压密阶段内部的微孔洞、微裂隙、宏观裂缝、层理被压实,损伤减小,页岩弹性模量不降反增,应力-应变曲线呈下凹型,首次提出受载岩石损伤先减小后增大,建立了更加合理的基于声发射特征的页岩单轴压缩损伤本构模型。

In order to obtain accurate damage evolution law and acoustic emission characteristics of loaded rocks(shales),improve the previous theory of monotonous damage increase of loaded rocks,and expand the understanding of the internal damage evolution mechanism of loaded rocks further,uniaxial compression acoustic emission tests on continental shales were conducted.The test results show that the process of rock uniaxial compression can be divided into four stages:compaction stage-elastic deformation stage-elastic-plastic deformation stage-post-peak failure stage.There are a few acoustic emission signals in compaction stage,elastic deformation stage and pre-elastic-plastic deformation stage.There are a lot of acoustic emission signals before and after peak stress.Especially in post-peak failure stage,acoustic emission signals rise sharply.Acoustic emission probe can capture rock compaction,crack propagation and communication.Acoustic emission signals can reflect micro-damage evolution process in shale.Rock damage evolution and acoustic emission characteristics in parallel and vertical bedding planes of shale are quite different,so the influence of bedding on rock mechanical properties can not be neglected for bedding rocks.In the stage of rock compaction,the micro-voids,micro-fissures,macro-fissures and bedding are compacted,the damage decreases,the elastic modulus of rock does not decrease but increases,and the stress-strain curve is concave.For the first time,it is proposed that the damage of loaded rock decreases first and then increases.A more reasonable constitutive model of uniaxial compression damage of shale based on acoustic emission characteristics is established.