Shocking failure mechanism of advanced coal pillars under the mining influence of shallow⁃buried closed distance coal seams

Chain shocking instability of residual coal pillars in front of the working face will induce the dynamic load disasters under the mining influence and affect the safe and efficient mining of the underlying coal seam. It is the basic premise of safe mining to reveal the advance chain⁃shock failure mechanism of coal pillars under the mining in⁃ fluences of shallow⁃buried closed distance coal seams. In this paper， the movement law of overburden strata during the mining of the 6107 working face in the Yuanbaowan Coal Mine was monitored and analyzed. The spring⁃ back deformation phenomenon of advanced coal pillars was found. The physical simulation experiment of underly⁃ ing coal seam mining under the room and pillar goaf was carried out. The deformation and failure characteristics of re⁃ sidual coal pillars and overburden strata were studied. The springback shocking failure process of advanced coal pillars under the mining influence was analyzed. The shocking failure mechanism was revealed. The results show that 1 Dur⁃ ing the mining process of shallow⁃buried closed distance underlying coal seam，the overburden strata in front of the working face present a deformation characteristics of former short⁃time springback and then severe subsidence. That is，the overburden strata firstly present a very short⁃term springback deformation phenomenon. Afterwards，there is an overall collapse phenomenon of overburden strata. As a result，the springback deformation fact of advanced coal pillars under the mining influence could also be obtained. 2 The key pillars are suffered the earliest oblique shear failure un⁃ der the strata subsidence and advanced bearing pressure，which causes the load transfer and redistribution. It would strengthen the stress concentration of adjacent coal pillars，and lead the chain and oblique shear failure. During this process，the overburden strata continue to subside. The fractures continue to develop and the shear breaking surface is generated. The collapsing and rotating of overburden strata also occur. It promotes the springback deformation and advance shocking of residual coal pillars in front of the working face，and causes the full⁃thickness cutting of interbur⁃ den strata. Finally，larger range of coal pillars suffer the chain failure and the dynamic disasters are caused in the un⁃ derlying working face. 3 The springback shocking failure process of advanced coal pillars under the mining influence of shallow⁃buried closed distance coal seam could be divided into four periods: the oblique shear failure period of key coal pillar，the failure period of key pillar and adjacent partial coal pillars，the springback shocking failure peri⁃ od of advanced coal pillars，and the disaster period caused by overburden strata collapsing and interburden strata cut⁃ ting. 4 The advance shock failure of residual coal pillars under the mining influence of shallow⁃buried closed dis⁃ tance coal seam is a dynamic process with the combined and mutual feedback effect of “springback deformation of coal pillars” and “linked collapse of overburden strata”. This study can explain the reason why the advanced dynamic load is generated in the underlying coal seam mining under the pillar goaf. It is expected to provide a theoretical guidance for the prediction and control of the advanced dynamic load pressure，which can further ensure the safety，green and high recovery⁃rate mining of close⁃distance coal seams.