Mechanism Of Preventing Dynamic Hazards Under Hard Roof By Solid Backfilling Technology

Hard roof is widely distributed in coal mines in China and hard to control. It is typicallycharacterized with high rock strength, large overhanging area and high bearing capacity.Rock burst, coal-gas outburst, goaf hurricane and many other dynamic hazards could beeasily induced when mining in such roof condition, thereby threatening the safe productionof mines. As an emerging green mining technology in recent years, solid backfill miningtechnique is remarked as a significant breakthrough in mining "three under" coal. It caneffectively control the strata movement and deformation, as well as weaken the stratabehavior to a large extent. Considering the problems mentioned above and the advantages ofsolid backfill mining, the dissertation proposes a new idea of exploiting the coal under thehard roof by employing solid backfill mining. In this dissertation, intergrated methos oftheoretical analysis, laboratory test, physical simulation, numerical simulation and in-situapplication is adopted. Characteristic energy dissipation of solid backfill material is testedand the mechanism of the hard roof-induced dynamic hazards and key prevention methodsare theoretically analyzed; the interrelation between backfill body and hard roof, energyvariation control, hazard prevention, roof deformation and energy distribution rules underdifferent roof-controlled backfilling ratios in the backfill workface are systematically studied.The dissertation also gives the design basis of roof-controlled backfilling ratio, which is thenapplied in the field application. The main innovative achievements are as follows:(1) The non-linear relationship between energy dissipation and strain of solid materialis obtained from the compaction tests. The energy variation in compaction process may beclarified into three stages: slow dissipation stage, speed-up dissipation stage and rapiddissipation stage. The effect of particle size, loading velocity and initial loading stress on theenergy dissipation of solid material is revealed.(2) Based upon energy evolution rules during the roof deformation and the causes ofdynamic hazards, this dissertation reveals the process of energy accumulating, transformingand releasing from the first exposure of hard roof to breaking down. Reducing theaccumulation and release of energy in workface is found to be the key factor to preventdynamic hazards. Considering the superiority in controlling strata movement by using solidbackfill method, the dissertation proposes a new idea of using solid backfilling mining toprevent the hard roof dynamic hazards.(3) By establishing a non-uniform segmented model of a beam on an elastic foundation, the equations of energy distribution and releasing before and after the hard roof breakingdown are given. The interaction between the backfilling body and the roof of under differentbackfilling ratios is studied by changing the elastic foundation coefficient. The model revealsthe effect of backfilling on deformation of hard roof and energy variation in workface.(4) Using physical simulation and numerical analysis, the stress and energy distributionin surrounding rock mass under different roof-controlled backfilling ratios are analyzed. Thisdissertation develops a basic design method of preventing hard roof dynamic hazards by solidbackfill mining, which is demonstrated feasible in the field application.