Mining-induced subsidence is critical for ecological environment reconstruction and damage prevention in coal mining areas. Understanding the characteristics of surface subsidence with multi-seam mining is the first step. Surface subsidence of different mining panel layout configurations was investigated by means of UDEC numerical simulation. Based on the simulation results, it was indicated that mining panel layout configuration had a significant impact on surface subsidence, including ground surface subsidence, horizontal displacement, crack propagation, and ground surface fissure development. The overlapped region of the upper panel and the lower panel is the key region, where existing bedding separations and strata cracks close and activate, the integrity and strength of the interburden layer are reduced, and the subsidence magnitude is enhanced. The subsidence profile of the overlapped region for the stacked configuration, external staggered, the edge of the lower panel internal staggered, two edges of the lower panel internal staggered are steeper and deeper, and the corresponding values of ground surface subsidence and horizontal displacement are greater than other regions. The ground surface fissures with the types of stepped, slided, and graben developed on the ground surface above the edge of the mining panel, and the development location is closely related to the strata movement edge. Because of the support activities of the reserved coal pillar, the ground subsidence of the external staggered (internal staggered) of the upper panel with the coal pillar is slight. The external staggered (internal staggered) and external staggered (internal staggered) of the upper panel with the coal pillar can be selected as the preferred layout configuration. The proposed description of surface subsidence of different mining panel layout configurations can be applied in subsidence prediction.

In order to research protected layer pressure relief effect under influence of different width of coal pillar, this paper carried on FLAC3D numerical simulation of vertical stress field and deformation field under different coal pillar width. The protected layer evolutional characteristics of vertical stress, vertical displacement and pressure relief affection which coal pillar affected were analyzed. The results show that: (1) Coal pillar affected zone is high stress concentrated zone. Because of coal pillar width influence, trended vertical stress distribution is from “v shape” to “partial saddle shape”; tendency vertical stress distribution is “flat disc shape”. Vertical stress is non-linear with coal pillar width, vertical stress is most concentrated when coal seam reserved 20m coal pillar, vertical stress distribution is from “single peak shape” to “double peak shape”. (2) Coal pillar affected zone is low strain region. Coal pillar decreases protected layer overall deformation, not just reduce deformation of coal pillar affected zone. Vertical deformation is negative correlation with coal pillar width. Trended vertical displacement distribution is “” shape; tendency vertical displacement distribution is “flat disc shape”. (3) Unprotected range increases with the increase of coal pillar width, pressure relief angle is 49°–60°, pressure relief angle of both sides is negative correlation with mined out areas. Engineering measurement shows: simulative results and experimental results are consistent. Research results have theoretical reference and practical significance on unprotected layer effect measurement and outburst elimination

The key parameters of pressure relief pre-splitting blasting technology (PRPBT) contribute to the implementation effect of goaf-side entry by roof cutting (GSERC). This study is an attempt to design the key parameters including the roof cutting height, the roof cutting angle, the spacing between blasting boreholes, the charge structure and the sealing length by using theoretical analysis, numerical simulation and field implementation. The basic quality index of the main roof is 666.27, and combined with the peeping observation result, the main roof belongs to the category of a hard main roof. Different from a weakened roof and a compound roof, the unreasonable parameters of the PRPBT for the hard main roof lead to three problems including an insufficient pre-splitting blasting effect, roof suspension in the goaf and serious damage to the rock mass for the roof cutting rib. The PRPBT effect is closely related to key parameters, including the roof cutting parameters and the pre-splitting blasting parameters. Hence, to solve those three problems, a new design strategy was proposed based on the optimized directions of increasing the roof cutting height, decreasing the spacing between the blasting boreholes, changing the charge structure and adjusting the sealing length. According to the results of the theoretical calculation, numerical simulation and in situ measurement, the roof cutting height, the roof cutting angle, the spaced distance between the blasting boreholes, the charge structure and the sealing length were determined as 10 m, 15°, 500 mm, 4 + 4 + 3 + 3 + 2 and 2.4 m, respectively. The fissure rate was proposed to assess the developed effect of different pre-splitting blasting schemes. The proposed design strategy achieved a better effect of pre-splitting blasting for the entry, and eliminated the roof suspension of the hard main roof in the goaf. The design strategy in this study could contribute to other similar coal mines under the condition of a hard main roof.