Failure mechanism and its control of surrounding rock for gob-side entry driving with narrow coal pillar in the working face with goaf on both sides

Aiming at the problems of controlling the large deformation and failure of surrounding rock of deep soft-broken coal roadway, the gob-side entry driving with narrow coal pillar in the working face mined on both sides of the deep soft-broken coal seam in a mine is taken as the engineering background, which is very difficult to control the surrounding rock. The main difficulties of surrounding rock of coal roadway control are analyzed, and the large deformation and failure mechanisms of surrounding rock of gob-side entry driving with narrow coal pillar are studied in FLAC^3D numerical simulation software. The results show that the stress adjustment and unloading caused by the mining disturbance at the large height working face, the overlying roof load of gob-side entry driving is mainly borne by the solid coal. It is concluded that the peak stress area of surrounding rock in gob-side entry driving with narrow coal pillar is mainly located in solid coal and its depth of shoulder angle, and its vertical stress concentration factor is as high as 3.04. It is clarified that the roof shoulder angle in solid coal, coal pillar and the shallow plasticized surrounding rock in solid coal are the key control areas. It is characterized that the maximum extension range of plastic zone of roof, solid coal and coal pillar is about 5.88 m, 2.50 m and 3.00 m respectively, and the sub-regional asymmetric failure mechanisms of surrounding rock in gob-side entry driving with narrow coal pillar are revealed. The analysis clarified that the anchoring foundation of anchor cables and other supporting components should be located in a relatively complete elastic zone in the deep part of surrounding rock during roadway support. Based on this, the sub-regional combined support technology of anchor beam mesh support + channel steel anchor cable reinforcement + grouting modification is proposed. Engineering practice has proved that the high-strength support reinforcement and grouting modification measures have effectively improved the stress state of surrounding rock in gob-side entry driving with narrow coal pillar in deep coal rock mass that is soft, broken and prone to large deformation and failure, and the deformation of the roof and two sides of gob-side entry driving in the test section are controlled within 500 mm. It ensures the safe and orderly mining of the working face with large-mining height and provides a reliable way for the effective control of the large deformation of surrounding rock in such deep soft-broken coal roadway.