不同冲击速度下含气砂岩损伤−渗流特性试验研究

Experimental study on damage and seepage features of gas bearing sandstone under different impact velocities loading

为探究不同冲击载荷作用下含气砂岩冲击损伤特征和渗透性规律,利用含瓦斯煤岩冲击损伤−渗流试验系统和工业显微CT扫描系统,设计并开展了三轴预应力状态下不同冲击速度加载的动态压缩−原位渗流试验,重构了受冲击损伤砂岩的三维裂隙结构,对比分析了固−气耦合试样不同冲击速度加载下的动态应力−应变曲线特征、能量耗散规律、破坏损伤和渗透性演变特征。研究结果表明:含气砂岩的应变率随冲击速度的增加而增加,入射波能、反射波能、透射波能和吸收能也随之逐渐增大。含气砂岩的峰值应力和峰值应变也随冲击速度的提升而逐渐增大,且动态应力−应变曲线的压密阶段不断被压缩直至完全消失。三轴固−气耦合动态冲击条件下,含气砂岩的破坏形式以剪切破坏为主;随着冲击速度的递增,冲击载荷与气体压力联合作用下含气砂岩内部的张拉裂隙数量不断增加,新生裂隙相互连接促使了宏观贯通裂隙的形成;泊松比效应和偏心压缩作用使砂岩上分别形成了沿试样轴向方向延伸和垂直于轴向方向延伸2种张拉裂隙,2种裂隙在试样外沿相互连通,呈现出网格状。含气砂岩的吸收能量直接决定了其损伤程度,吸收能量的不断增加,不仅加大了含气砂岩破坏后的损伤程度,也大幅提高了含气砂岩的渗透性;冲击受损破坏之后的含气砂岩渗透率与其裂隙率遵循线性正相关关系。

Using an impact damage-percolation experimental system for gas bearing coal or rock and an industrial CT scanning system,the authors design and carry out a series of dynamic compression-seepage tests for loading at different impact velocities under triaxial prestressed states and reconstruct the three-dimensional crevices structure of the impact-damaged sandstone in order to reveal the law of damage features and permeability of the gas bearing sandstone under different impact loads.The experimental results of dynamic stress-strain curve characteristics,energy dissipation laws,damage and permeability evolution features under different impact velocities loading of fluid-solid coupling sandstone samples show that as the impact loading velocity increases,the strain rate of the gas bearing sandstone increases.The incident wave energy,reflection wave energy,transmission wave energy and absorption energy increase simultaneously as well.The peak stress and peak strain of gas bearing sandstone increase with the impact velocity as well,and the compaction stage in the dynamic stress-strain curve is constantly compressed until it disappears completely.The failure form of gas bearing sandstone is mainly shear failure under the condition of triaxial static and gas-solid coupling.With the increase of impact velocity,the number of tensile cracks under the combination of impact load and gas pressure increases continuously.Poisson's ratio effect and eccentric compression form two types of tensile cracks along the axial direction or perpendicular to the sample.The two types of tensile cracks are connected along the outer edge of the specimen,showing a grid shape.Nascent cracks are interconnected,which drives macroscopic through cracks formation.The absorption energy of gas bearing sandstone directly determines the degree of damage.The increasing absorption energy not only increases the damage degree of gas bearing sandstone after damage,but also greatly improves the permeability.The permeability of gas bearing sandstone after impact damage follows a linear positive correlation with its crack rate.