考虑卸荷作用的底板突水破坏机制研究

Water inrush failure mechanism of mining floor under unloading effect

在依据摩尔图解及断裂力学理论对底板卸荷突水破坏分析的基础上,运用损伤断裂力学并结合统一强度理论,建立了考虑渗透水压作用下分支裂纹端部形成的塑性区范围计算方程与岩体发生贯穿破坏时的损伤阀值。将裂纹扩展过程与岩体损伤耦合起来,确定了裂纹的损伤断裂能量计算公式并分析了其影响因素。结果表明:侧压系数λ=0.5时,最大主应力完全卸荷状态下裂纹端部应力强度因子比双轴应力状态下大,岩体易发生破坏。考虑了裂纹端部塑性区的影响,裂纹损伤断裂能量相比于不考虑其影响时偏大,增大了煤层底板突水的危险性。裂纹损伤断裂能量G_1与裂纹半长a、裂纹面连通面积与总面积之比α、裂纹面渗透水压p及最小主应力σ_3呈正相关,与裂纹面摩擦系数f及岩体的弹性模量E呈负相关。分析结果为底板突水破坏机制研究提供了一定的参考依据。

To further understand the failure mechanism of water inrush from mining face floor, the water inrush failure mechanism of mining floor is analyzed using the Mohr diagram and fracture mechanics theory. By considering the effect of saturated pressure on the branching crack tip, an analytical formula for the plastic fractured region and a damage threshold of rock mass failure are established with damage fracture mechanics and the unified strength theory. An equation of damage fracture energy is determined by coupling crack propagation and rock damage, and the factors influencing the damage fracture energy are analyzed in depth. The results show that the stress intensity factor（SIF） of the crack tip at the complete unloading state of the maximum principal stress is higher than that at the biaxial stress state with a confining pressure coefficient λ= 0.5, in which the mining floor has been found to be more prone to failure. By taking into account the influence of the plastic fractured region of the branching crack tip, it is noted that the crack damage fracture energy G_1 tends to be higher and water inrush risk of mining floor is more obvious. There is a positive correlation between G_ 1 and the crack half-length a, the ratio of crack connected area to the crack total area α, crack seepage pressure p and the minimum principal stress σ_3. Whereas it shows a negative correlation with the friction coefficient of crack surface f and modulus of rock mass E. The results provide some insights into the prediction of water inrush failure mechanism of mining floor.