载荷方式对深部采动煤体损伤-渗透时效特性影响实验研究

Effects of the loading methods on the damage-permeability aging characteristics of deep mining coal

根据煤体实际力学状态设定恒定围压增加轴压、恒定轴压卸除围压和同时增加轴压卸除围压等3种力学路径,开展加卸载煤体损伤-渗透同步实验,分析加卸载方式对采动煤体损伤-渗透时效特性的影响,并揭示采动煤体损伤-渗透特性差异的内在机制.研究结果表明:不同的力学路径使煤体表现出截然不同的变形与强度特征,在高围压作用下试样的变形特性逐渐从脆性向塑性转变;受加卸载方式的影响,3种力学路径下的试样分别发生主剪切破坏、拉剪破坏和X型共轭剪切破坏;不同的力学路径对试样造成不同程度的损伤扩容和渗透率变化,且具有明显的时效特性,按响应速度排序依次是:同时增加轴压卸除围压>恒定轴压卸除围压>恒定围压增加轴压;煤体损伤、渗透具有协同演化特性,但渗透率变化相对于损伤扩容具有滞后性;差应力比是导致加卸载煤体损伤-渗透特性差异的本质原因,承受较大差应力比的深部采动煤体极易诱发煤岩瓦斯动力灾害,为避免动力灾害发生,需采取相应措施减小采动煤体所受的差应力比.研究结果对于揭示煤岩瓦斯动力灾害机理、实现深部煤炭精准开采与动力灾害防治具有指导作用.

Three mechanical paths were set based on the actual mechanic status of coal,which includes fixing confining pressure and increasing axial pressure,fixing axial pressure and decreasing confining pressure,and increasing axial pressure and decreasing confining pressure.Then the damage-permeability experiments for gassy coal were performed.The effects of the loading methods on the damage-permeability aging characteristics of mining coal were analyzed and the internal mechanism for the diversity of damage and permeability characteristics was revealed.The results show that the coal mass with different mechanical paths present distinct deformation and strength properties,and the coal would gradually shift from brittle to plastic with the effects of high confining pressure.The coal mass with the three mechanical paths were fractured with the forms of principal shear,tension shear and X conjugate shear.The various degrees and obvious aging characteristics of the irreversible damage and permeability changes were caused by the different mechanical paths of the coal mass.The coal damage and permeability are evolved jointly but the permeability lags behind the damage.The different deviatoric stress ratio is the fundamental cause for damage.Permeability characteristics diversity of plastic coal and the coal mass with great deviatoric stress ratio would induce the coal gas dynamic hazards more easily.The measurements should be taken to decrease the deviatoric stress ratio of the coal in order to avoid the dynamic hazards.The findings have directive significance in aspects such as revealing the mechanism of dynamic hazards,prevention for the hazard and precise mining of deep coal.