Evolution law and control method of plastic zone in soft weak roof of mining roadway

Under the condition of weak roof, the mining induced roadway will have a large depth of plastic failure zone under the superposition of the original rock stress and the mining stress, which will cause severe deformation of the surrounding rock of the roadway, and even the hidden danger of roof fall. In order to grasp the evolution law of the plastic zone in the weak roof during mining, taking the mining roadway of Mindong No. 1 Mine as the engineering background, the distribution and evolution characteristics of the plastic zone of the roadway surrounding rock before and after mining have been systematically studied. The results show that:under the superimposed influence of the advanced supporting pressure and the side supporting pressure of the mined-out area in the upper section, the ratio of the two principal stresses around the mining roadway increases sharply. At the same time, the surrounding rock of the roadway is affected by the migration of the adjacent coal face. The direction of the maximum principal stress in the peripheral stress will also be largely deflected. With the continuous evolution of the magnitude and direction of the main stress of the surrounding rock in the mining roadway with a weak roof, the maximum plastic fracture depth gradually expands towards the roof. During the expansion of the plastic zone, the distribution of barriers will appear. The severe roof deformation is mainly caused by plastic failure. The rupture sequence of the roof of each layer is shallow plastic failure, high soft rock plastic failure, and middle rock rupture. The fracture failure of the middle layer generally lags behind the formation of the high-level penetrating plastic zone. During this period, the surrounding rock of the roadway appeared serious non-uniform large deformation, and it was extremely difficult to support. Based on this, a roof control method with grouting anchor cable as the core is proposed. The grouting layer should be mainly concentrated on the layer where high penetration plastic failure occurs during mining, and the grouting coverage should not be less than the high penetration plastic failure. The roof deformation monitoring results of the roadway show that the roof control effect is good, the roof has no safety hazards and the deformation is within the allowable range.