Reasonable parameters of roof cutting entry retaining in thin immediate roof and large mining height fully-mechanized face

At the large height mining face with thin immediate roof,the goaf cannot be timely filled after roof caving, the overlying hard-and-thick roof forms a cantilever beam structure laterally on working surface,and the overburden pressure is transmitted to roadway,which causes the surrounding rock to be unstable. Taking the condition of thin immediate roof and hard-and-thick basic roof at the 12408 working face of a mine as the engineering background,using a combination of theoretical analysis,numerical simulation and on-site monitoring,the reasonable parameters of the roof cutting entry retaining at the fully-mechanized mining face with the thin immediate roof and large mining height are studied. The roof mechanical model of the roof cutting entry retaining is established. The relationship between the ten- sile stress of the non-penetrating surface (TSNPS) and the cutting height and cutting angle is quantified,and the vari- ation of TSNPS with the height and angle of cutting top is determined. It is concluded that TSNPS and the cutting height are approximately exponential distribution when the cutting angle is fixed,TSNPS increases with the increase of the cutting height,and the growth rate gradually increases. When the cutting height is constant,TSNPS changes along with the cutting angle in a parabolic shape,as the cutting height increases,the range of the cutting angle required to exceed the limit of TSNPS also increases. The numerical simulation method is used to analyze the variation law of the axial force variation factor of the anchor cable,the distribution characteristics of the vertical stress of section coal pillar and adjacent roadway,and determine that the cutting height of 11 m and the angle of more than 0 degree can cut the stress transfer. Considering the complex and varied conditions of rock formation,the unevenness of the slit surface after blasting,the difference in the degree of penetration and the smooth fall of the thick-and-hard roof under the pressure of the mine,the site uses a 13. 6 m cutting height and a 10 degree cutting angle. Combined with the bulking coefficient, the theory verifies that the roof caving height is greater than the actual height of the working face,that is,the roof ca- ving can support the overlying strata early and reduce the influence of overburden movement on the stability of the roadway and coal pillar. On-site monitoring shows the deformations of the roof and floor and two sides of the roadway are small,and the surrounding rock is relatively stable. The reliability of the numerical simulation results and the feasi- bility of roof cutting and pressure relief are verified,which can provide a reference for the roof cutting entry retaining with similar conditions.