Study On Stress-Fracture Evolution Of Overburden And Mining Failure Characteristics Of Roadway In Close Distance Coal Seam

The stress disturbance produced in the mining of close coal seam plays an important role in the stability of roadway surrounding rock,and the factors such as the spatial position structure between two coal seams and the distance between coal seams will have obvious adverse effects on the mining of lower coal seam.Based on the fracture characteristics of overlying strata on two working faces and the stress distribution characteristics of roadway surrounding rock,this thesis adopted theoretical analysis,finite element and discrete element numerical simulation,similar material simulation experiment and other research methods,aiming at the mine strata behaviors law of overlying strata and the stress distribution characteristics of roadway surrounding rock under different spatial overlapping positions.Especially the evolution law of stress and fracture in two working faces under secondary mining.The relationship between different overlapping positions of working face and surrounding rock stress of mining roadway in lower coal seam is established.The characteristics of overburden strata behaviors in the lower working face and the distribution characteristics of roadway surrounding rock stress are revealed.It provides a theoretical basis for effective control of roadway surrounding rock of lower working face in close distance coal seam mining.The main work and achievements are as follows:(1)By similar material simulation test and numerical simulation test,the evolution law of leading abutment pressure in the working face under primary and secondary mining in close distance coal seam mining is compared and analyzed.The leading abutment pressure of the upper working face shows a stable "slow growth" evolution law.In the part of the lower working face that passes through the upper working face goaf in the advancing direction,the working face floor stress exhibits the evolution law of "slow growth-rapid growth-rapid pressure relief-slow growth-slow pressure relief".In the part of advancing direction that does not pass through the upper working face goaf,the working face floor stress shows the evolution law of "rapid growth,slow growth,stable and constant".(2)The influence of upper working face mined-out area on stress evolution law of lower working face in the process of close distance coal seam mining was studied.The overlying rock is a single stress concentration shell in the goaf of the working face..When the lower working face is mined the open-off cut of upper working face,the overburden of the two working faces suddenly sink as a whole,and two single stress concentration shells develop into left low right high ’’M-shaped’’ stress concentration shells.After the completion of the lower working face mining,two working face overlying rock formed left high right low ’’M-shaped’’ stress concentration shell.(3)The influence of the goaf in the upper working face on the evolution law of the overlying rock fracture in the lower working face is studied in close distance coal seam mining.When the working face is mining the coal seam in the zone without stress disturbance,overburden rock "trapezoidal" collapse.When the lower working face is mined and the upper working face is cut to the lower side,the strata between the two working faces are broken,and the overburden of the two working faces then falls across as a whole.After entering the goaf of the upper working face,the strata between the two working faces collapse in a two-dimensional plane "parallelogram",and the overlying rock collapse of the upper working face lags behind the strata between the two working faces.(4)Failure characteristics of roadway surrounding rock under stress peak at different working face overlap positions are studied.The overall magnitude of shear strain increment in different parts of surrounding rock of lower working face mining roadway from large to small is roof,roadway,shoulder and floor.The low stress concentration area of the unsupported roadway surrounding rock is located in the shallow part of the roadway surrounding rock,and the high stress concentration area is located in the deep part of roadway surrounding rock,and the tension-shear failure area is concentrated in the shallow part of roadway roof and floor and both sides,and the tension-shear failure area is more fully developed.After support,the low stress concentration area and high stress concentration area of roadway surrounding rock are close to the shallow part of roadway surrounding rock and the stress increases significantly compared with that without support,the shear failure area is smaller than that without support,the shear failure trace is more fully developed,and the shear failure trace of roadway roof and floor is developed to the two sides of roadway.