不同冲击方向下高压气体致裂岩石特征试验

Experimental study on characteristics of rock fracturing by high-pressure gas under different impact directions

为探索含瓦斯煤层增透性,提高抽采率,利用自主研制的真三轴高压气体冲击致裂岩石试验系统,开展不同冲击方向下高压气体致裂试验,试验变量为气体冲击方向与最大水平主应力的夹角,在三向应力的作用下开展高压气体冲击试验,得到冲击方向与最大水平主应力呈现0、30、45、60和90°夹角时岩石破裂形态及声发射响应。结果表明:高压气体冲击致裂岩石过程呈现5个显著阶段,即冲击起裂阶段、气压上升阶段、裂缝扩展阶段、气压稳定阶段和压力衰减阶段;高压气体冲击产生垂直裂缝和水平裂缝,射流角度增加后,垂直裂缝出现偏转,且偏转角度逐渐变大,裂缝偏转点也逐渐远离钻孔,水平断裂面呈现中间低四周高的形态;气体峰值压力随着射流方向与最大主应力的角度增加而增加,从0~90°峰值压力呈线性增长;分析声发射信号发现,岩石冲击破坏以张拉破坏为主、剪切破坏为辅,但随着射流角度增加,逐渐转变为剪切破坏为主的拉-剪复合破坏。

To explore the enhanced permeability of gas-containing coal seams and improve extraction efficiency,high-pressure gas fracturing tests under different impact directions were performed by a self-developed true triaxial high-pressure gas impact rock fracturing test system.The test variable was the angle between gas impact direction and maximum horizontal principal stress.High-pressure gas impact tests were performed under the actions of three triaxial stress,and rock fracture morphology and acoustic emission response were obtained at angles between the impact direction and the maximum horizontal principal stress of 0,30,45,60,and 90°.The results indicated that the rock fracturing process caused by high-pressure gas presented five significant stages including the impact crack initiation stage,air pressure rising stage,crack propagation stage,air pressure stabilization stage,and pressure attenuation stage;High-pressure gas impact caused vertical and horizontal cracks.Vertical cracks were deflected,and the deflection angle increased with the increment of the jet angle.Moreover,the crack deflection points gradually moved away from the drilling hole,and the horizontal fracture surface took on a shape of low in the middle and high in surrounding areas.The maximum gas pressure increased with the angle between the jet direction and the maximum principal stress,and the peak pressure represented a linear increment from 0 to 90°;The acoustic emission signals analysis indicated that rock impact failure was primarily caused by tensile failure and supplemented by shear failure.However,as the jet angle increased,it gradually became a tensile-shear composite failure dominated by shear failure.