炭质泥岩渐进破坏过程的变形特性及损伤演化研究

Study on the Deformation Characteristics and Damage Evolution Law of the Progressive Failure Process of Carbonaceous Mudstone

为研究软岩渐进破坏过程的变形特性和损伤演化规律,通过对炭质泥岩开展不同围压的三轴压缩试验,分析了围压对炭质泥岩宏观力学特性的影响;并将损伤岩石细观模型概化为岩石颗粒、裂隙损伤和孔隙3个部分;根据岩石细观结构损伤机制,结合应力-应变曲线特征,分段建立了炭质泥岩损伤演化方程:压密阶段,以孔隙率为损伤变量,建立了考虑孔隙压缩变形的损伤方程;线弹性阶段,假定岩石颗粒与孔隙变形协调,建立损伤方程;裂隙扩展阶段,通过建立岩石颗粒微元体转化为裂隙损伤微元体的函数,以裂隙和孔隙率为损伤变量,提出考虑裂隙扩展的损伤方程。结果表明:炭质泥岩应力-应变曲线非线性特征明显,可分为压密阶段、线弹性阶段、裂隙扩展阶段和峰后阶段;随着围压增大,炭质泥岩闭合应力、起裂应力和峰值应力线性增大;应力-应变曲线的压密阶段缩短,裂隙扩展阶段延长,延性特征增强。建立的损伤演化方程能较好反映岩石渐进破坏过程的演化损伤规律,表现出:压密阶段损伤非线性减小,线弹性阶段损伤保持非零稳定,裂隙扩展阶段损伤加速增大,峰后阶段损伤减速增加;围压抑制炭质泥岩损伤发展,随围压增大,压密阶段损伤加速减小,裂隙扩展阶段损伤延缓增加,且损伤增长速率减小。

To study the deformation characteristics and damage evolution law of the progressive failure process of soft rock,triaxial compression tests under different confining pressures were conducted on carbonaceous mudstone.The influence of confining pressure on the macro-mechanical properties of the carbonaceous mudstone was analyzed.Additionally,a mesoscopic model of damaged rock was simplified to include three parts:rock particles,fissure damage,and pores.According to the mesoscopic damage mechanisms combined with the characteristics of stress-strain curves,a damage evolution equation for carbonaceous mudstone was established in four stages.In the compaction stage,porosity was used as a damage variable and a damage equation considering pore compression deformation was established.In the online elastic stage,by assuming that the rock particles were coordinated with the pore deformation,another damage equation was established.In the fissure expansion stage,by establishing a function for transforming rock particle micro-elements into fissure damage micro-elements and considering the crack rate and porosity as damage variables,a damage equation considering crack expansion was developed.The results can be summarized as follows.(1)The nonlinear stress-strain curve characteristics of carbonaceous mudstone are clear and can be divided into a compaction stage,linear elastic stage,crack expansion stage,and post-peak stage.The closing stress,crack initiation stress,and peak stress increase linearly with increasing confining pressure.As the confining pressure increases,the stress-strain curve of carbonaceous mudstone becomes steeper,the compaction stage is shortened,the crack expansion stage is prolonged,and the deformation characteristic ductility is enhanced.(2)The established damage evolution equation can accurately reflect the evolutionary damage law of the four stages in the progressive failure process of rock.Damage is nonlinearly reduced in the compaction stage,remains as non-zero stable damage in the linear elastic stage,accelerates in the crack expansion stage,and decelerates in the post-peak period.(3)Confining pressure inhibits the development of carbonaceous mudstone damage.As the confining pressure increases,damage during the compaction stage accelerates.Additionally,the damage in the crack expansion stage is delayed and the damage growth rate decreases.