Temporal-spatial evolutionary law of plastic zone and stability control in repetitive mining roadway

In view of the serious deformation and destruction of surrounding rock,the difficulty of support and the hid- den roof fall hazard affected by repetitive mining in the retained roadway,the temporal-spatial evolution laws of stress and surrounding rock plastic zone were studied in the 22205 air return roadway in Buertai Colliery by the comprehen- sive analysis methods including theoretical analysis,numerical simulation and field test. The whole dynamic failure process of roadway surrounding rock from excavation stability to abandonment and the static spatial expression of rounding rock failure state at different positions are obtained. The dynamic-static combination mechanism of plastic zone variation in repeated mining roadway is expounded. The results show that ① there is a corresponding relationship between the time and the spatial zone of the plastic zone expansion in the mining process and the specific range of the spatial zone is obtained according to the field measurement,which are important foundations in analyzing the mecha- nism of roadway deformation and putting forward the support plan in different stages. ② The asymmetric expansion mechanism of the plastic zone is obtained. Its range is determined by the magnitude of deviatoric stress,and its orienta- tion is dominated by the direction of principal stress. The combined action of the magnitude of deviatoric stress and an- gle causes the asymmetric expansion of plastic zone,and then generates asymmetric deformation,so the mechanical mechanism of temporal-spatial expansion in the plastic zone of repetitive mining roadway is revealed. ③ According to the expansion form of plastic zone,the depth and range of plastic zone expand significantly in the primary mining process,and the roof and floor are obviously larger than the two sides. In the process of secondary mining,the plastic zone depth changes little but the range increases obviously,which mainly occurs at the top angle of coal wall and the bottom angle of coal pillar. ④ Based on the temporal-spatial relationship of plastic zone expansion during repeated mining,a method of fractional reinforcement support is proposed to solve the stability control of surrounding rock in re- peated mining roadway. According to the expansion form of plastic zone and field test,it should clearly determine the reinforcing time,position and parameters,and provide a reinforcing roof bolting to save work time and guarantee the mining safety in production.