循环应力损伤对煤体冲击倾向性影响研究

Research on the influence of cyclic stress damage on coal bursting liability

目前对煤岩体动力学行为特征的研究仅考虑了温度、围压等原始地质作用影响,并未考虑煤炭开采过程中产生的循环应力作用对煤体动力学特性的影响;且对煤体动力学显现特征的判定是以煤体冲击倾向性指标为基本依据,而循环应力损伤作用对煤体冲击倾向性及其动力学特性的影响尚未进行深入研究。针对上述问题,对煤样开展了循环应力损伤试验,分析了恒上下限及变上限2种循环应力损伤条件下的煤体冲击倾向性变化特征。试验结果表明:①煤体经恒上下限循环应力作用及变上限循环应力作用后静态抗压强度分别降低了13.86%与16.00%,循环应力会对煤体力学强度产生劣化。②原始煤体剩余弹性能指数为27.34kJ·m^(-3),表示该煤体具有弱冲击倾向性,经过恒上下限循环应力损伤及变上限循环应力损伤后煤体剩余弹性能指数分别降低了约26.30%及36.14%,表明循环应力对煤体的冲击倾向性有显著的弱化作用。③随着煤体剩余弹性能指数的降低,煤体动态抗压强度与动态弹性模量均减小,而动态破坏变形不断增大,表明煤体冲击倾向性将直接影响其动力学特征,煤体冲击倾向性越大,其冲击动力学相关参数劣化程度越高。④随着煤体剩余弹性能指数不断降低,冲击后煤体破碎分形维数降低,表明循环应力使得煤体受冲击后崩解不充分,动力学响应减弱。

Currently,research on the dynamic behavior features of coal and rock masses only considers the influence of original geological processes such as temperature and confining pressure,without considering the impact of cyclic stress generated during coal mining on the dynamic features of coal.And the determination of the dynamic features of coal is based on the index of coal bursting liability.The impact of cyclic stress damage on coal bursting liability and its dynamic features has not been thoroughly studied.In order to solve the above problems,cyclic stress damage tests are conducted on coal samples.The variation features of coal bursting liability under two cyclic stress damage conditions,namely constant upper and lower limits and variable upper limits,are analyzed.The experimental results show the following points.The static compressive strength of coal under the action of constant upper and lower limit cyclic stress and variable upper limit cyclic stress has decreased by 13.86%and 16.00%,respectively.Cyclic stress can degrade the mechanical strength of coal.②The remaining elastic energy index of the original coal body is 27.34 kJ·m^(-3).It indicates that the coal body has a weak bursting liability.After constant upper and lower limit cyclic stress damage and variable upper limit cyclic stress damage,the remaining elastic energy index of the coal body has decreased by about 26.30%and 36.14%,respectively.It indicates that cyclic stress has a significant weakening effect on the bursting liability of the coal body.As the remaining elastic energy index of the coal decreases,the dynamic compressive strength and dynamic elastic modulus of the coal decrease,while the dynamic failure deformation continuously increases.It indicates that the bursting liability of the coal will directly affect its dynamic features.The greater the bursting liability of the coal,the higher the degree of degradation of its impact dynamics related parameters.@As the remaining elastic energy index of the coal body continues to decrease,the fractal dimension of coal fragmentation after impact decreases.It indicates that cyclic stress leads to insufficient disintegration of the coal body after impact and weakened dynamic response.