Abstract
The mechanical model of the basic roof fracture structure is established on the basis of key block theory to study the roof breaking mechanism of gob‐side entry retaining under roof cutting and pressure relief, and the analytical formula of roof support resistance is derived when the key block of the basic roof is stable. The influence of roof cutting angle and cutting height on roof support resistance is also analyzed. Determining the cutting seam parameters of the retained roadway roof is necessary to identify the support resistance of the roadway roof due to the correlation between the roof cutting parameters and the support resistance. Taking the II 632 haulage drift of the Hengyuan coal mine as the engineering background, FLAC3D numerical simulation is used in this paper to analyze the influence of different roof cutting angles and cutting heights on the surrounding rock structure evolution of retained roadways. Results show that the roof cutting angle and cutting height respond to the support resistance of the retained roadway roof, and the support resistance required by the roof increases with the roof cutting angle and cutting height. This condition ensures that the side roof of the gob can be cut off smoothly, and the support resistance required by the roof of retained roadways is within a reasonable range. Through theoretical and numerical simulation analysis, the reasonable roof cutting height of II 632 haulage drift is 8 m and the roof cutting angle is 15°. The theoretical analysis and numerical simulation results reveal that the required support resistance to maintain the stability of the roadway roof is 0.38 MPa. The supporting scheme of the roof of the II 632 haulage drift in the Hengyuan coal mine is then designed. Finally, the field industrial test is used for verification. The borehole imaging results show that the overall line of the retained roadway roof is small based on the description of field monitoring results. The deformation of the surrounding rock surface of the retained roadway is less than 100 mm, and the roadway is 40 m from the lagging working face. The deformation rate of surrounding rock decreases with the increase in distance from the working face. The integrity of the retained roadway roof is good, and the deformation of the surrounding rock is effectively controlled.
Highlights
Owing to the increasing contradiction between the daily reduction of coal resources and energy demand, the roof cutting and pressure relief technology in gob-side entry retaining can effectively reduce the waste of coal resources [1,2,3,4]
Reference [10] analyzed the application of the new telescopic energy absorption support system on the surrounding rock of the retained roadway by the numerical simulation method and found that the new support system is conducive to maintain the stability of the retained roadway roof compared with the traditional support method
Reference [12] theoretically analyzed the broken position of the retained roadway roof and concluded through the assessment of UDEC numerical simulation software that the fracture of the retained roadway roof on one side of the goaf is conducive to the roadway stability
Summary
Owing to the increasing contradiction between the daily reduction of coal resources and energy demand, the roof cutting and pressure relief technology in gob-side entry retaining can effectively reduce the waste of coal resources [1,2,3,4]. E research results of many scholars revealed that the roadway roof with gob-side entry retaining can effectively solve the roadway deformation problem through the roof cutting and pressure relief technology despite the broken roof of the retained roadway or its short cantilever beam structure, which is closely related to the roof cutting angle and height. 2. Roof Breaking Mechanism of Gob-Side Entry Retaining with Roof Cutting and Pressure Relief e research results of many scholars on the structural characteristics of roof strata of mining roadway [22, 23] show the rapid collapse of the strata in the goaf behind the support with the advancement of the mining face. In the gob-side entry retaining technology of roof cutting and pressure relief, one side of the roadway is solid coal, and the other side is the rock block caving area in the goaf.
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