Surrounding rock deformation mechanism of roadways with extra-thick coal seam

The surrounding rock deformation mechanism of roadways with extra-thick coal seam (RETCS) is of significant importance to further study controlling strategies and reduce coal roadways accidents in the underground coal mines. In order to obtain deformation characteristics of the roof and coal sides to RETCS, a systematic method including field observation, experimental test, theoretical analysis, in situ monitoring and mechanical calculation is proposed. Analysis of two typical RETCS shows deformation characteristics of large displacement, weak supporting stability and easy to collapse. Based on field observation, roof deformation mechanism in bolt supporting was thoroughly studied with theoretical method. Results show that roof deformation development started from the bedding separation, which indicates of great importance to effectively control the occurrence and extension of bedding separation zone. Combined with numerical simulation with FLAC 3D software, a total of 6 key influence factors to displacement of surrounding rock of RETCS and prestress field distribution characteristics to bolt supporting were determined, and then both of the minimum safety controlling ranges calculation formulas respectively to roof and coal sides were deduced by building different mechanical models. With above researching results, Field investigation in No.2 colliery in Pingshuo Group was undertaken to obtain the mechanical parameters of coal seam by experimental test and then concluded the deformation characteristics after achieving the monitoring displacement data, which could afford guidance to supporting designs of RETCS.