裂隙岩体宏细观剪切损伤力学行为研究

Investigation on the macro-meso shear damage mechanical behaviors of fractured rocks

采用室内直剪试验和PFC^(2D)细观模拟的手段,分析不同加载情况下裂隙岩体的剪切变形、强度特征及损伤演化规律。研究结果表明:(1)裂隙岩体剪切强度变形曲线可分为压密阶段、近似线弹性工作阶段、不稳定发展阶段和残余变形阶段。(2)裂隙岩体峰值剪切位移与裂隙数量N、法向应力σ和剪切速率ν均呈负相关,峰值剪切应力与N和ν呈负相关,与σ呈正相关,且N越大ν对峰值剪切位移的影响越明显,ν越大N对峰值剪切位移的影响越明显。(3)随着剪切位移的增加,各模型细观损伤裂纹(剪裂纹和拉裂纹)数量可分为微增(Ⅰ)→陡增(Ⅱ)→缓增(Ⅲ)三个阶段,摩擦耗散能逐渐增大,弹性应变能先增大后减小,破坏时岩体弹性应变能仅占细观损伤总能量的1/5~2/5。(4)模型宏细观裂纹于预置裂隙尖端萌生、扩展、贯通,最终中部岩桥以张拉破坏为主,两侧为剪(拉)–拉剪–剪破坏;倾角45°的单裂隙(M2)、Z型裂隙、X型裂隙和圆孔类岩体的峰值剪切应力和位移大小依次为X型>M2>圆孔类>Z型,损伤裂纹萌生于裂隙岩体的预置裂隙尖端以及圆孔类岩体的孔洞顶部和孔洞左下方,X型和M2岩体的裂纹分布基本一致。

The laboratory direct shear test and PFC^(2D)microscopic simulation were used to investigate the shear deformation,strength characteristics and damage evolution law of fractured rocks.The research results show that:(1)The shear strength-deformation curve of fractured rocks can be divided into four stages:compaction stage,approximate linear elastic stage,unstable development stage and residual deformation stage.(2)The peak shear deformation of fractured rocks is negatively correlated with the number of fractures(N),the normal stress(σ)and the shear rate(ν).And the peak shear stress of fractured rocks is negatively correlated with N andν,while positively correlated withσ.Besides,the greater N is,the more obvious the effect ofνon the peak shear deformation is,and the greaterνis,the more significant the effect of N on peak shear deformation is.(3)With increasing the shear deformation,the number of meso-damage cracks(shear cracks and tensile cracks)increases with the variation characteristics of slight(Ⅰ)→steep(Ⅱ)→slow(Ⅲ).The frictional dissipation energy gradually increases,the elastic strain energy first increases and then decreases.Especially,the elastic strain energy of rock mass only accounts for1/5~2/5 of the total energy of mesoscopic damage.(4)At the tip of the preset cracks,the micro-meso cracks initiate,expand and then penetrate.In the end,the central rock bridge is mainly damaged by tensile,and the failure modes of two sides shows shear(tensile)failure-tensile-shear failure-shear failure.The peak shear stress(displacement)is X-type>M2>round-hole>Z-type.The damage cracks appear at the tip of pre-existing flaw,and also the top or bottom left of the hole.The distribution of cracks is basically the same for the X-type and M2 fractured rocks.