Study on strata stress and deformation response of contiguous seams under cutting roof for entry retaining

In order to deeply understand the deformation evolution law of overburden stress of contiguous seams under cutting roof for entry retaining, taking the transportation drift 2442, 2443 and 2444 in B₄ coal seam, B₃ coal seam and B₂ coal seam of Baijiao Coal Mine as the research object, the excavation physical test of 3 coal seams was carried out, the results show that: ①after cutting the roof of roadway in upper coal seam, the roof is relieved; after coal excavation, the goaf roof caves and supports the roadway roof, leading to roof pressurizing; with the further excavation of coal seam, the overburden fractures, the roof pressure is relieved again; the roof stress of roadway goes through the process of pressure relief, pressure increase and pressure relief successively, among which, the stress of upper roof increases greatly and the stress is higher.②After cutting the roof of the central roadway and coal seam excavation, the pressure of overburden is transferred to the surrounding rock of the upper coal seam roadway and the subsidence crushed and compacted surrounding rock of the roadway, the stress-concentrated area is formed in the overburden between the two roadways. ③The surrounding rock is seriously damaged and without concentrated stress after roof cutting of the lower roadway and coal seam excavation, which are greatly affected by the pressure relief of the first two excavations. ④Dislocation deformation and vertical tensile shear cracks appeares along the roof rock mass, and the greater the subsidence influence, the greater the crack propagation degree.