Study of a no-pillar mining technique with automatically formed gob-side entry retaining for longwall mining in coal mines

To reduce the roadway drivage ratio, drivage cost, and safety accidents, and increase the resource recovery ratio, a no-pillar mining technique with automatically formed gob-side entry retaining is proposed for longwall mining. In this technique, pressure is offloaded via directional roof cutting, and a roadway is automatically formed via the ground pressure and rock breaking expansion. These processes permit the implementation of a new longwall mining process in which there is no mining roadway and no reserves of coal pillars. In this paper, the concepts and key techniques (the technique of directional roof cutting, the formation technique of integrated coal side of the automatically formed gob-side entry retaining, the formation technique of gob-side gangue rib, and the support technique using a constant-resistance and large-deformation anchor cable) of no-pillar mining with automatically formed gob-side entry retaining are introduced, and a field engineering test is performed. The test results are as follows: the no-pillar mining concepts and technique with automatically formed gob-side entry retaining are feasible; all techniques and processes fully satisfy field production requirements; and the deformation of the automatically formed gob-side entry retaining is small, and the control effect is significant. These results prove that the no-pillar mining technique with automatically formed gob-side entry retaining is feasible for longwall mining and achieves the goal of safe and efficient mining.