煤层巷道围岩破断失稳演化特征和分区支护研究

Evolution characteristics of fracture and instability in coal roadways and sub-regional supporting

为研究煤层巷道围岩失稳过程及裂隙演化特征,并对支护方式选择提出建议,通过数值模拟获得工作面附近围岩应力分布特征,并将围岩受力状态简化成平面应变问题、准平面应变问题和三维复杂应力问题3种。采用自行研制的相似材料模拟试验台及煤岩体细观力学试验装置,分别针对平面应变和准平面应变2种应力状态下煤岩体的破坏过程及裂隙演化特征进行试验研究。结果表明:1)层状围岩梯形巷道受载失稳存在3个阶段,即楔形破坏阶段、滑移失稳阶段、顶底板大挠度断裂阶段。高垂直应力条件下,顶、底板初始变形造成两帮出现明显剪切滑移后,直接顶、底板分别出现"三铰拱"形态冒落及鼓胀断裂。2)准平面应变条件下,煤体自由端首先出现张拉破裂失稳,造成上覆直接顶砂岩受力不均,并出现一次弯曲断裂;随载荷增大,煤体出现滑移失稳并呈现出"弧线"压出形态,顶板砂岩发生断裂;裂隙煤体与砂岩反复作用形成多对贯通裂隙,说明顶板断裂位置、形态与煤体失稳过程具有显著的对应关系。结合压剪和拉伸破坏机理,对单一煤层巷道和沿空留巷煤层巷道围岩的支护进行分区研究,并提出相应的支护建议。

To study the process and characteristics of fracture and failure development in the coal roadways, and offer appropriate supporting suggestions, the stress distribution of the surrounding rock near working face was obtained through the numerical simulation. The stress state of the surrounding rock was reduced to plane strain problem, the quasi-plane strain problem, and complex three-dimen- sional stress problem. With similar material simulation test device developed by us and the coal-rock meso mechanical test device, the failure process and the evolution characteristics of fracture of sur- rounding rock was analyzed under the stress state of the plane strain and quasi-plane strain. The resultshave shown that 1） There are three stages of instability process of layered surrounding rock of the trapezoidal roadway： stage of wedge destruction, stage of sliding instability, and stage of large deflec- tion fracture of roof and floor. Under the conditions of high vertical stress, the initial deformation of the roof and floor caused shear slip to occur in the two sides of roadway. After that, caving with the shape of ＂three hinged arch＂ and bulge fracture occurred in the immediate roof and floor respectively; 2） Under the quasi-plane strain condition, tensile failure first appeared at the free face of the coal, resulting in uneven force in the overlying sandstone roof, and a bending fracture occurred; with the load increasing, slip and instability occurred in the coal and it showed the extrusion of the ＂arc shape＂. Simultaneous, rupture appeared in the sandstone roof; there were multiple pairs of interconnected fractures in the coal and sandstone during their repeated action. This shows a significant correlation among the fracture posi- tion, morphology, and coal instability process. Based on the mechanism of shear and tensile failure, the sub-regional supporting of a single roadway and gob-side entry retaining was analyzed, and suggestions to the supporting were put forward.