Study On The Rule Of Fracture Of Multi-composite Key Strata And Top Coal Weakening Process Based On Highly Tough Coal Seam With Partings

Fully mechanized sublevel caving method features high efficiency,simple production system,and strong adaptability to variations in coal seam thickness,and is a common process for improving production efficiency and coal output at the working face.However,for some special and complex geological conditions,it is often manifested as low top coal caving rate and poor coal caving effect,resulting in a large amount of waste of coal resources.In this paper,the geological conditions of multi-composite key strata in Yushutian Coal Mine of Xinjiang and the high toughness top coal with gangue in 110501 fully mechanized caving face are taken as the research background.The research methods of theoretical analysis,experimental test,numerical simulation,mechanical calculation and engineering inspection are combined to explore the external causes and internal mechanism of top coal difficult to break.The cyclic weakening process of top coal is designed.The construction effect is evaluated by a number of detection indexes after engineering application.While reducing the waste of coal resources,the crushing degree and fluidity of top coal are effectively improved,the hidden dangers of gas explosion and mine fire are eliminated,and the sustainable development of mine is promoted.It provides a reference for the weakening process of top coal under similar complex engineering conditions.The main results are as follows:(1)The physical and mechanical parameters of as density,uniaxial compressive strength,elastic modulus,tensile strength,cohesion and internal friction angle of the coal and rock mass in the mine were measured by field sampling and laboratory test,and the hard roof of the working face was graded,which provided basic parameters for the numerical simulation and mechanical calculation in the later stage.(2)The external reasons for the difficulty of top coal caving in working face are studied.The position of the composite rock strata was determined and the key strata of the overlying strata were identified.According to the multi-layer composite key strata identified,the UDEC numerical model was established to observe the caving of the top coal in the working face,the calculation results of the fracture of the overlying strata and the stress of the support,and the fracture law of the multi-composite key strata was studied.(3)The internal mechanism of difficult top coal caving in working face was analyzed.The LS-DYNA numerical model of high toughness top coal blasting weakening was established to study the influence of high toughness on top coal crushing.At the same time,the self-supporting mechanical model of top coal containing gangue was established to study the influence of multi-layer thick gangue layer on top coal crushing.On the basis of this theory,the problems existing in the original weakening process are analyzed,and the top coal cyclic weakening process conforming to the conditions of high toughness gangue top coal is proposed,and the technical feasibility,economy and environmental protection of the process are evaluated.(4)The special design of the top coal circulation weakening process is applied to the engineering practical problems.The multi-functional composite drilling field is designed and arranged.After the three construction links of the drilling charge initiation,gas rapid extraction and dynamic-static pressure water injection,the effect of top coal weakening is evaluated by three indexes: the average crushing degree of the borehole,the cumulative displacement of the top coal and the top coal discharge rate.This paper has 85 figures,19 tables and 101 references.