Study on Variation Law of Ground Pressure before and after Hard Roof Fracturing

Abstract

Hard roof has the characteristics of small fracture development, good structural integrity and strong integrity, and the hanging roof area is large during mining, which seriously threatens the safety production of working face.Based on the characteristics of hard roof such as high strength, large thickness and difficulty in self-caving, directional drilling hydraulic fracturing is adopted to destroy the structural stability of hard roof and make it reach an ideal fracture form. At the same time, the variation law of strata behavior in working face before and after fracturing of hard roof is explored.The results show that:①During the normal weighting period of hard roof working face, the support pressure of working face is generally small, but when the hard roof is broken, it will cause the phenomenon of strong weighting in working face, which threatens safe production;②Hydraulic fracturing leads to secondary development of primary fractures in hard roof and continuous diffusion in the form of fracture network, which destroys the original bearing structure of hard roof and forces hard roof to collapse ahead of time;③Thirdly, comparing the weighting law of working face before and after fracturing, it is found that after pressure relief, the initial weighting step of working face decreases by 50.8 m, which is 56.4% year-on-year, and the average periodic weighting step decreases by 3.7 m, which is 21.4% year-on-year. After pressure relief, there is no strong strata behavior in working face, and hydraulic fracturing achieves the expected effect.