Deformation and failure rules of underlying roadway of cross mining in ultra-thinness coal seam

Aiming at the problem of deformation and destruction of the overlying roadway of overhead-mining in very thin seam, the research methods of measuring the roadway loosening circle and 3D laser scanner to monitor the deformation of the roadway using geological radar are studied. The monitoring results show that the severe deformation of the roadway does not occur around the corresponding working face, but is located in tens of meters behind the working face. Its deformation form is the overall floor heave, up to 287.4 mm; no obvious subsidence failure occurred on both shoulders and roof of roadway. The cause of the damage to the roadway is: due to the impact of mining, the damage of the overlying rock layer on the roadway causes the water in the goaf of the upper working face of the roadway to flow into the surrounding of the roadway along the cracks, and the excavation of the surface allows the stress in the vertical direction of the roadway to be released, causing the floor of the roadway to rise upward. In view of the large deformation of the roadway under the influence of cross mining, it is recommended to reduce the row spacing of the U-shaped steel telescopic support from 1 m to 0.8 m for similar situations.