Structural evolution of breaking roof group of multiple coal seams and its influence on lower coal seam mining

Based on theoretical analysis,numerical simulation and field monitoring,an evolution model of breaking roof group structure of multi-coal seams was established,the development and extension height of breaking roof group were derived when mining successive coal seams,and the formula of mining face support strength was given under the interaction of remained coal pillars and breaking roof group.Subsequently,the extension law of breaking roof group height was studied using numerical simulation and the site validation was also carried out.The results show that: the space between the coal seams of Jurassic system is small and the interval layer is easily broken and connected to the caving and broken roof structure of upper coal seam which leads to the formation of a breaking roof group structure.Though the space between Jurassic and Carboniferous system is large,the weight of breaking roof group of Jurassic system passes down through remained coal pillars and acts on the mining face support together with breaking roof group strata of Carboniferous system,which results in the significant increase of support pressure in mining face of Carboniferous system and strong ground pressure occurs.This paper explains the reason why strong ground pressure appears in lower coal seam when mining multiple coal seams,which could provide the basis for the surrounding rock control in multi-coal seams mining at Datong mining area and similar coal mines.