There is a close correlation between near surface loads and the"activation"of old goafs in steeply inclined coal seams.The rock blocks at the bottom of the fractured zone in the overlying rock of the goaf are prone to rotational instability and sliding instability under load.These rock blocks play a cru-cial role in the stability of the goaf and are known as key rock blocks.When the load causes key rock blocks to become unstable,goaf"activation"will occur.In this paper,based on the mechanical model of the"masonry beam"structure of the overlying rock in the goaf,the mechanical analysis of the key rock block is carried out,and the judgment basis of the instability of the overlying rock mass in the goaf under the load is constructed,and then the stability of the overlying rock mass in the steeply inclined coal seam under the load is quantitatively analyzed.The study shows that when the maximum friction force applied to the soil section is greater than the maximum shear force of the soil,the block will not slide and lose stability.Only when the average extrusion stress between the key rock block and the rock block is less than the extrusion strength of the rock block at the corner,the key rock block will not undergo rotational instability.The derived results are applied to a steeply inclined coal mine in Guangdong Province,the results show that the laying of gas pipelines above the goafs of 4 and 6 coal seams in Chashan Coal Mine will not cause the"activation"of the goafs.The mechanical analysis of key rock blocks under load has a good application effect in the stability of overlying rock mass in the steeply inclined coal seam,which has a certain guiding effect in practical engineering.
long-distance pipelinegoaf of steeply inclined coal seamtheory of masonry beamsoverlying rock mass stability
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