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In order to research protected layer pressure relief effect under influence of different width of coal pillar, this paper carried on FLAC 3D 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.

In order to research the law of mine pressure and roof control in shallow buried coal seam, based on a comprehensive summary of mine pressure theory, technology application, engineering practice, summarized research results and status, analyzed research shortage, proposed research proposals. The results show that:1“short masonry beam” and “step beam” structure mechanical model and “key stratum in shallow seam theory” has provided theory basis for coal seam roof control shallow guidance. 2Rock and soil (bedrock and alluvium) coupling mechanism, loose layer dynamic structure theory," coal mining, water retention, ecology conservation, subsidence control" optimized portfolio on management theory and technical system of is the required research direction. 3Sichuan, Yunnan, Guizhou, representative of southwest mountainous shallow buried coal seam mining pressure research is conducive to development of mining pressure theory system.