Study on optimization of supporting technology for large cross-section open-off cut under contiguous gob

In view of the complex deformation of large-section open-off cuts and related chamber in surrounding rocks under contiguous mined-out area and the insufficient research on reliability verification and optimization of the supporting structure under this working condition,the deformation and stress of surrounding rock and support structure were simulated and calculated during open-off cut excavation under the mined-out area by FLAC3D and ANSYS numerical simulation software,and the supporting technology and related parameters were optimized. The deformation and stress concentration state of surrounding rock under different support row spacings were compared,and the rationality of the support scheme was verified by field engineering application and actual measurement of surrounding rock deformation. The results show that the initial breaking distance of the open-cut roof without support is 19.6 m and the periodic fracture distance is 8 m under the condition of no support. Therefore,the maximum lag distance should not be more than 8 m when supporting the roof. Numerical simulation calculations show that when the supporting row spacing is 1 m,the roof subsidence reduction rate can reach 38.73% in the combined supporting section of bolt,metal shed,and hydraulic prop. When the row spacing is densified to 0.5 m,the effect of roof subsidence reduction is significantly improved,the roof subsidence reduction rate in the middle of the open-off cut is more than 60%,and the subsidence of the middle roof is reduced to less than 20 mm after the densification of support row spacing,which fully meets the requirements of roof support. The on-site monitoring results show that the maximum subsidence value of the roof is 12 mm and the maximum separation distance is 6 mm and the roof control effect is good. The optimized scheme has significant effects on roof subsidence control and stress reduction of the roof.