| Roadway support is one of the eternal themes of coal mining.With the improvement of roadway support technology,especially the large-scale application of high-strength and ultra-high-strength bolts,roof fall accidents in coal mine roadways due to support failure have gradually decreased.However,in the southwest region,coal mine roof accidents still occur more frequently,and the number of roof fall accidents accounts for more than 60% of coal mine accidents,far exceeding the national average of 44.41%.The reason is that the roofs of coal mines in Southwestern China are basically characterized by thin layers and multilayers.In the range that affects the stability of the surrounding rock of the roadway,there are often 5 to 10 or even more than a dozen coal and rock layers.With the increase of mining depth,it is more difficult to support the coal mine's thin-bedded and multi-layered surrounding rock roadway.At present,for the efficient and safe mining of coal mines in southwestern China,the support of thin-bedded and multi-layered surrounding rock roadway is one of the main constraints.Aiming at the problem that it is difficult to effectively support the thin-bedded and multi-layered surrounding rock roadway,this study combines physical test,theoretical analysis,numerical simulation,and industrial test to investigate the failure mechanism of thin-layered multilayer physical surrounding rock,and on this basis,the principle of bolt support under this condition is proposed,and it is verified by numerical simulation and on-site industrial test.(1)Shear experiments on layered rock materials under loaded conditions are carried out.The experimental results show that the shear strength of the bedding of rock-like materials increases with the increase of the normal stress,and the relationship between the shear strength of the bedding and the normal stress of the specimen can be better depicted by the Coulomb criterion.The experimental results also found that the particle size of the layered surface after the sample is broken will be smaller if the normal stress is larger.(2)Determine the principle of the bolts controlling the thin-layered multi-layered surrounding rock roadway.Based on the results of experiment and theoretical analysis,The support of thin-bedded multi-layered surrounding rock roadway is mainly through increasing the normal squeezing force of the bedding surface to improve the mechanical strength of the bedding surface.Based on this,the principle of bolts controlling thin-layered and multi-layered surrounding rock roadways is proposed,that is,to increase the pre-stress and anchoring length of bolts.A mechanical model was established,and the stability characteristics of the surrounding rock of the roadway were discussed.(3)Through numerical simulation,the effect of pre-stress on the effect of bolt supporting thin-bedded surrounding rock roadway is explored.The results show: With the increase of the bolt support prestress,both the displacement of the roadway surface and the range of the plastic zone decrease;the greater the angle between the bolt and the bedding surface,the smaller the deformation of the bedding surface monitoring point,the more conducive to the role of the bolt;the overall stability of the roadway surrounding rock can be improved due to the strengthened internal friction angle and cohesion within the anchorage zone of the roadway surrounding rock,which is caused by the prestressed bolt support.(4)The stability of bedding surface surrounding rock with different inclination angles affected by the prestressed bolt support is investigated through numerical simulation.It can be concluded from the results: the horizontal and vertical deformations of the bedding plane first increase and then decrease as the inclination angle of the bedding plane increases,showing a "?" type change characteristic;are supported.The plastic zone of the rock masses of the bedding planes with different dip angles has "angle effect" after support;The inclination of the bedding surface will affect the stress concentration range of the surrounding rock of the roadway;with the increase of the dip angle,the bedding surface changes from shear failure to tension failure between layers;In the intersection of roadway and bedding tendencies,the deformation of the roadway is more significant.For the layered rock mass with large dip angle,ultra-high-strength active support should be adopted in the initial support.(5)Based on the study of layered rock mass,the bolt support scheme of W22602 return airway in Datong No.1 Mine was optimized.On-site industrial tests showed that high-strength,high-prestressed anchors and full-length bolts were used to support thin-layered multi-layered roadways.It is reliable,and further verifies the mechanism of the bolt supporting the thin-layered multi-layered surrounding rock roadway proposed in the paper. |
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