煤岩组合体的能量演化规律与破坏机制

Energy evolution law and failure mechanism of coal-rock combined specimen

为研究煤岩组合结构受压过程中的能量演化规律与破坏机制,对煤、岩石及3组煤岩组合体进行了单轴一次加载与循环加卸载试验,分析了煤岩组合体输入能密度、弹性能密度、耗散能密度以及弹性模量与单轴抗压强度等力学参数的演化规律,得到了不同试样的储能特性,基于煤岩组合体的力学响应、能量演化与变形破坏特征,建立并探讨了煤岩组合体破坏的能量驱动机制。结果表明:煤岩组合体峰前阶段的输入能密度、弹性能密度及耗散能密度随轴向应力的增加呈明显的非线性增长特征,峰前阶段的能量密度-应力曲线可分为压密段、弹性变形段和非稳定破裂发展阶段,整个过程储存在试样内部的弹性能较高,耗散能较少,试样达到屈服后,耗散能所占比例开始增加。煤岩组合体的单轴抗压强度与弹性模量介于纯煤和岩石试件中间,更接近于纯煤试件,随着岩石强度的增大,组合体力学性能稍有增强,但幅度有限,煤体是控制组合体强度等力学特性的主要因素。煤岩组合体破坏的能量驱动机制可概括为:煤岩组合体受压过程中,煤、岩开始不断储存弹性应变能,煤体储能速度快,内部弹性能达到其储能极限时,煤体率先发生破坏,破碎程度高,主要呈X状共轭斜面剪切破坏,破坏瞬间释放的能量传递至岩石,达到岩石的储能极限时,煤体中裂纹扩展贯通至岩石内部,在弹性能的驱动下岩石发生张拉破坏。

In order to study the energy evolution and failure mechanism of coal-rock combined structures during loading process,the uniaxial one-time loading and cyclic loading and unloading tests were carried out on coal,rock and three sets of coal-rock combined specimens.The evolution of the input energy density,elastic energy density,dissipated energy density,elastic modulus and uniaxial compressive strength of coal-rock combined specimens were evaluated,and the energy storage characteristics of different samples were obtained.Based on the mechanical response,the energy evolution and deformation and failure characteristics of coal-rock combined specimens,and the energy-driven mechanism of coal and rock combined specimen were established and discussed.The results show that the input energy density,elastic energy density and dissipated energy density of the coal-rock combined specimen in the pre-peak stage exhibit distinct nonlinear growth characteristics with the increase of the axial stress,the energy density-stress curve of the pre-peak stage can be divided into compaction section,elastic deformation section and unsteady fracture development stage,the ratio of elastic energy stored inside the sample is high,and the proportion of dissipated energy is small,after the sample reaches yield,the proportion of dissipated energy begins to increase.The uniaxial compressive strength and elastic modulus of coal-rock combined specimens are slightly greater than the pure coal and much lower than the rock specimens.The mechanical properties of the combined specimens increase slightly with the rock strength.This increase is limited due to the fact that the coal is the dominated factor controlling the mechanical properties of the combined strength.The energy-driven mechanism of coal-rock combination failure can be summarized as that during the loading process of the coal-rock combined specimen,the coal and the rock begin to store elastic energy continuously,the energy storage speed of coal is fast,when the internal elastic energy reaches the energy storage limit,shear failure initially occurs within the coal,leading to a X-shaped conjugate slope.When the energy released by the destruction is transmitted to the rock and reaches the energy storage limit of the rock,the crack in the coal expands into the interior of the rock,causing a tensile failure of the rock.