不同围压下深井煤岩短时蠕变试验的细观损伤机制分析

Mesoscopic damage mechanism of coal seam and rock mass in deep field under different confining pressures by short period creep tests

分析深井煤岩试验断口上矿物、结构、构造等的细观特征,追溯围压对其蠕变损伤机制的影响及调节作用,得到了围压分别为0、10和20 MPa的深井煤岩短时分级加载蠕变试验破坏断口的细观构造,分别对应解理断裂-节理裂隙、沿晶界断裂、沿晶界断裂-穿晶断裂。围压为0 MPa的单轴蠕变试验破坏断口,是煤岩受简单应力环境直接作用的结果,因此,其解理断裂和节理裂隙构造清晰、方向明确、内部新鲜且无夹杂。围压为10 MPa三轴蠕变破坏断口的沿晶界断裂间隙较宽、内部不干净、充填碎屑类夹杂,表明较强环向约束下的晶界较易于克服,且矿物结构以晶粒间的切向运动及力矩作用下的晶粒转动方式调整。围压为20 MPa的三轴蠕变试验,环向强约束使得晶界与晶粒的强度难以克服,最终破坏断口上的沿晶界断裂主要呈现弧形转动,穿晶断裂以剪切位移为主要特征,所以沿晶界断裂构造不太干净、内部充填围压先期作用时原生构造闭合后新产生的少量碎屑类夹杂,穿晶断裂间隙极小、新鲜、干净无夹杂。

This paper is to investigate mesoscopic features of coal seam and rock mass in the deep field,which includes the mineral,configuration,and structure of the fractured surface of specimens.The effect of confining pressure on creep damage mechanism and its regulation were also studied.Under short period creep loading,the observed mesoscopic features were classified into cleavage fracture-joint fractures,intergranular fracture,and intergranular-transgranular fractures under confining pressures of 0,10,and 20 MPa,respectively.Under the confining pressure of 0 MPa（i.e.,the uniaxial creep test）,the failure fracture was caused by the simple stress acting on coal seam and rock masses directly.As a result,its cleavage fracture and joint fissure had distinct structure,clear orientation,and fresh interior without inclusions.Under the confining pressure of 10 MPa,the interface of intergranular fracture was found to be relatively wide,and the interior was not clear and filled with inclusions.It indicated that the grain boundary was easily broken under the higher confining pressure,and the mineral structure was changed by adjusting both the tangential movement among grains and the grain rotation under the action of torque.Under the confining pressure of 20 MPa,since the grain boundary was restricted and grain itself was difficult to be destroyed,the ultimate destruction of the fracture along the grain boundary fracture mainly showed the arc rotation.Besides,the siginificant feature of transgranular fractures was characterized by the shear displacement.Under strong restrictions,intergranular fracture structure was not clean and filled with little new inclusion caused by the earlier period of confining pressure.In contrast,the transgranular fracture was tiny,fresh,and pure without inclusions.