Research on key technology of gob-sideentry by roof cutting with complex roof condition

In view of the problem of the roadway scrapping caused by the failure of the retaining bodies such as anchorage, anchor cable and single column in the initial stage of the gob-side entry retaining by cutting roof in Dianping Mine, the method of detecting the lithology of the roof of the roadway was adopted to analyze the key problems of the gob-side entry retaining by cutting roof under the complex roof conditions. By establishing the surrounding rock stability structure and its mechanical model, the influence of the cutting height of the cutting seam and the rock swell on the basic roof movement, the supporting principle of the NPR anchor cable to the roof and the shear action of the hydraulic prop to the roof on the side of the cutting seam were analyzed. It is pointed out that the roof movement of retaining roadway can be divided into three periods: direct roof caving period, basic roof fracture subsidence period and compaction stability period. The parameter design of the constant-resistance anchor cable support and the retaining dynamic pressure period support should be calculated based on the most intense period of roof movement. The theoretical formula of the key technical parameters, such as the pre-splitting of roof, constant resistance support and the temporary support during the dynamic pressure period were given. Combined with the surrounding rock characteristics of each section of the roadway, the experimental roadway was divided into 7 sections. The key technical parameters of the roadway were optimized.Through the analysis of the mine pressure data of the roadway on site, the top plate movement was severe in the 0～60 m lag working surface, and the roof movement was severe. The lag working surface was 60～160 m, which was the compaction of the fallen waste rock. At the stage, the roof movement was slow; after the lag working surface reached 160 m, the deformation of the surrounding rock gradually stabilized. The field application shows that the cumulative deformation of the roof and floor and two sides of the retaining roadway are 1 200 mm and 1 420 mm respectively at the initial stage, and the roadway retraction rate is 54%. After subsection optimization, those are controlled below 420 mm and 435 mm, the shrinkage rate is below 18%, and the effect of deformation control of surrounding rock is good.