Study On Failure Mechanism And Repair Technology In Soft Rock Large Deformation Roadway

With the increase of mining depth,the problem of large deformation soft rock roadway is becoming more and more prominent,which has become one of the difficulties of roadway support.This paper takes the problem of large deformation of soft rock in No.I south cross-cut in Hancheng Xiangshan Coal Mine and the difficulty of support after repeated repairs,the large deformation of soft rock and failure characteristics and instability mechanism of roadway are researched,by using the combination method of site sampling and deformation measuring,physical simulation,theoretical analysis and project analogy and validation of numerical calculation,and eventually,the effective optimum supporting scheme for surrounding rock of roadway are put forward.Based on site sampling and measurement,it is shown that the roadway surrounding rock has the characteristics of low strength and softening in water,and the softening coefficient is 0.37-0.66.By means of the slice micrography and X-ray diffraction tests on the surrounding rock samples,and the clay mineral content in the surrounding rock was 17%?37%.Among them,montmorillonite content is 2%-4%,kaolinite content is 12%-29%.,illite content is 3%-4%.By observing the convergence deformation of No.1 south cross-cut(lasting 80 days),it is concluded that the floor heave,the two sides moving closer and the roof sinking are obvious in the whole section of No.1 south cross-cut,which shows the deformation around the roadway.The deformation is more serious especially the roof of coal seam and the floor of mudstone,the deformation of roof subsidence and floor heave can reach more than 50-100 cm and the approximation of two sides can reach more than 150-220 cm;After the roadway is repaired,it still shows continuous deformation,with the approximation velocity of two sides averaging 2.3 mm/d,and the approximation velocity of roof and floor averaging 2.1 mm/d.Physical simulation shows that after the roadway is affected by mining,floor heave first occurs,floor failure depth is 1.5m,roof failure height is 4.73m,two sides failure depth is more than 1.5m.According to the calculation and analysis of "ultimate self-stable arch theory",the breaking range and supporting parameters of roadway surrounding rock are determined as follows:the ultimate self-stable arch height of roof is 4.26m,and the length of roof anchor cable is 6m,the destruction depth of two sides is 1.86m,and the length of bolts of two sides and roof is 2.4m.Through numerical calculation(FLAC3D),comparing the optimized support with the original support,the depth of the plastic zone on both sides of the roadway is reduced by 80%,the depth of the plastic zone on the floor is reduced by 61%,the subsidence of the roof is reduced by 41%,the floor heave is reduced by 82.5%,the proximity of the two sides is reduced by 88%,and the deformation of the surrounding rock is effectively controlled.According to the deformation and failure characteristics of the roadway,the support scheme is put forward in the way of subsection treatment:in the 0-200m range of No.1 south cross-cut,the surrounding rock of the roadway is seriously broken,and bolt-shotcrete and grouting support are needed,in the range of 200-306m,the surrounding rock mass is relatively complete,36#U-shaped steel support is used to cooperate with reverse arch and bolt-shotcrete support in necessary areas.