(1. State Key Laboratory for Geomechanics and Deep Underground Engineering,China University of Mining and Technology (Beijing),Beijing 100083,China;2. School of Mechanics and Civil Engineering,China University of Mining and
Technology(Beijing),Beijing 100083,China)
Abstract:Gangue rib control is one of the biggest challenges for gob-side entry retaining formed by roof fracturing in thick coal seams. In this paper,the mechanism and control techniques for gangue rib deformations were systematically investigated using theoretical analysis,numerical simulation and field experimental methods. First,mechanical and numerical models were developed respectively to explore the dynamic impact behaviors of the gangue body for different mining heights. Based upon the obtained results,a multi-level control approach was proposed to address the instability problem of the gangue rib in thick coal seams. The results indicate that as the mining height increased,the impact force acted on the gangue prevention structure increased accordingly. The intense impact of the gangue body initiated the deformation of the conventional gangue prevention structure,and the roof sagging accelerated further its failure process. The severe impact area was within 6 m from the active mining panel,and an impact prevention device was designed to dissipate the impact energy. The variation of the lateral pressure was gentler within the compression area of the gangue rib. An individual support structure of sliding-type characterized by pressure release was designed and tested. Laboratory tests showed that the sliding-type structure coordinated effectively with the roof deformation,and thus improved massively its recycling utilization ratio. The anchor bolt of wave-type with multi-resistances was invented to further improve the monolithic stability of the gangue rib. Field pullout tests proved that the reinforcement effects of the structure were remarkable,especially when the structures were 60 m or far behind the active mining panel. The monitored results showed that the rib deformation decreased by appropriately 72% and the damage rate of the gangue prevention structures reduced by appropriately 85% after adopting the new approach. The proposed approach not only solved the rib control problems,but also brought about remarkable economic benefits.
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