Research On Breaking Law And Control Of Hard Roof In Fully Mechanized Caving Face Of Extra-thick Coal Seam

The study on breaking law and control of roof is very important to the prevention and control of strong mine pressure in fully mechanized top coal caving face of extra-thick seam under the condition of hard roof.Therefore,the thesis focuses on the fracture of hard roof and its control.Taking the hard roof of W1123 working face in Kuanggou Coal Mine as the research object,theoretical analysis,physical simulation,numerical calculation and field monitoring is used to study the breaking law and control of hard roof in the fully mechanized caving face of extra-thick coal seam,and achieved the following results.Systematically completed the analysis of the working face mining conditions,there are three kinds of hard strata in the overlying strata of the working face:thick-hard direct roof,inferior key stratum and main key stratum,by the mechanical model of clamped beam and cantilever beam,the initial breaking distance of the hard strata is 78.06-106.9m,and the periodic breaking distance is 22.03-43.82m.A physical simulation experiment was constructed to reveal the characteristics of overlying strata failure,stata behavior,overburden microseismic event distribution and energy evolution,when thick-hard direct roof and key stratum first collapse in goaf,strong weighting and high-energy microseismic events are induced,from 0 to 87.0m away from the goaf of overburden,the stress concentration of strata increases the microseismic energy produced by failure and the weighting strength of working face.Under the goaf,the failure rate of thick-hard direct roof and inferior key stratum of the working face destroy slowly along the trend,and periodic breakage of strata along the strike results in periodic weighting and intensive microseismic events with greater intensity.The stress and energy distribution characteristics of the thick-hard direct roof in different failure states of overburden are analyzed by using 3DEC numerical calculation,before the first collapse of thick-hard direct roof and key stratum,the stress and energy of roof in advance working face are at a higher level,and the stress and energy of roof in the junction area between overburden solid coal and goaf are highly concentrated;the stress reduction and energy release in the roof under goaf,the thick-hard direct roof is not easy to be destroyed along the inclination.In view of the characteristics of strong mine pressure induced by breaking and instability of thick-hard direct roof and key stratum in B2 extra-thick coal seam,the deep hole blasting technology is used to pre-crack the thick-hard direct roof and key stratum in the advanced working face,weaken the strength of the hard strata,and verified the roof blasting effect by comprehensive site borehole peeping,microseismic monitoring and support resistance observation,thus ensuring the safe production of the working face.The research results from this thesis provide theoretical support for ensuring the timely collapse of the hard roof of B2 fully mechanized top coal caving face in Kuanggou Coal Mine and reducing the weighting strength in working face,ensuring the safe and efficient mining of the working face,and providing reference and demonstration for the safe and efficient mining in fully mechanized top coal caving face of extra-thick coal seam under similar hard roof conditions in China.