| It is one of the most common problems of strong ground pressure in coal mine that the serious deformation and failure of the goaf-side retained roadway with hard strata.For this situation,pressure relief by directional roof cutting is effective to solve the problems.However,there is no research in 3D breaking characteristics of overburden for working face by roof cutting,and research methods of revealing 3D strata break,movement and stress filed evolution laws in the stope.Therefore,it is hard to accurately obtain the internal relations between the 3D break and movement characteristics and mine pressure laws.Besides,the existing roof cutting technology is hard to make fracture planes directional and continuous.Under such background,a new method of3 D strata collapse numerical simulation was developed based on Voronoi random polygon theory.Then the small-deflection theory for elastic thin plates was combined to study the effects of roof cutting on 3D breaking characteristics of overburden in the goaf,structural characteristics and stress distribution characteristics at the stope.Finally,the evolution laws and mechanisms of stress field of the working face by the method of roof cutting were revealed.The pressure relief technology by directional roof cutting was further developed for hard roofs,and the process and parameters of roof cutting technology were optimized.The proposed new method has been successfully used in8311 working faces of Tashan Coal Mine.The main conclusion and innovation points are given,as follows:(1)In order to reveal 3D break and movement process of strata and stress field evolution laws at the stope,considering the overburden structure,3D plate structure,and rock fracture mechanism,a new method of 3D strata collapse numerical simulation was proposed based on Voronoi random polygon theory,and a new program was developed.The reliability was verified from multiple levels.The new method could be used to study the 3D fracture and movement laws of overburden.(2)Based on small-deflection theory for elastic thin plates,hard strata 3D fracture mechanical models under 9 kinds of combined fixed/simply supported/free boundary conditions were established.They were used to explore the influences of roof cutting methods on basic roof fracture and periodic fracture laws and reveal the strong mine pressure control mechanism by changing basic roof breaking characteristics by the method of roof cutting.(3)The proposed 3D strata collapse new procedure could be used to get the relations between the basic roof fracture and strong ground pressure at the stope.3D structural characteristics of the overburden of the goaf were obtained,featured by“lower suspended plates at the boundary + irregular heap up in the middle + hinged plates at the top”.Besides,the mine pressure distribution laws were also obtained.Finally,the stress field of the stope evolution laws were revealed,which was triggered by overburden breaking characteristics by the method of roof cutting.(4)This paper reveals the pressure relief mechanism of coal pillar in hard roof by of directional roof cutting and determines the cutting range of rock strata.The process and parameters of roof cutting technological were optimized.For the first time,they were successfully applied in practice and lowered the stress of coal pillars significantly.(5)A method of determining the stable distance of the goaf was put forward.It was found out that the increase of roof cutting depth was useful for the stability of the goaf.The mechanism of double-peak stress of gob-side coal pillars in the goaf was revealed,which could provide theoretical basis for roadway driving time and layout of the small coal pillar mining method,and the determination of withdrawal distance of the temporary support equipment during non-pillar mining method.There are 132 figures,22 tables and 216 references. |
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