Failure Characteristics Of Direct Roof With Different Thickness Of Roadway And Bolt Support Technology

The direct roof of roadway is a common roof structure in the mining process of layered deposits.Under the condition of the change of the thickness of the direct roof,there are many different failure characteristics,such as flexural failure,overall caving and arch caving.In engineering,the roof is maintained by anchoring a large number of bolts to form a bearing structure.However,due to the large difference of stress distribution and failure path of the roof under different failure characteristics,the bolt support effect is greatly reduced,which has an impact on the safety and stability of underground production.In order to improve the bolt supporting effect of the direct roof of the roadway,the research was carried out from three aspects: the deformation characteristics of the roof,the stress distribution of the bolt and the selection of the bolt type.A systematic bolt supporting scheme,supporting parameters and the determination and calculation method of the bolt type of the direct roof of the roadway were constructed.In order to reveal the failure rule of the direct roof of the roadway,a targeted support scheme was designed.Based on the mechanical analysis,the rock beam block mechanical model of the direct roof was constructed,and the relationship between the failure characteristics of the roof and the thickness of the roof was revealed: with the increase of the thickness of the roof,the bending failure of the roof gradually changes into the overall caving and arch caving.In a certain range,the caving height increases with the increase of roof thickness.By deducing the relationship function between the thickness of roof and the failure characteristics of roof,the criteria of different failure characteristics of roof were established.On this basis,the method of bolt support scheme and bolt spacing parameters under different failure characteristics was determined,which improved the pertinence of bolt support scheme design for direct roof of roadway with different failure characteristics.In order to obtain the length of bolt support of roadway direct roof under the change of thickness.Considering the influence of the deformation difference and the thickness of the direct roof on the stress distribution of the bolt,the stress distribution model of the bolt passing through the two layers of rock was constructed.Through the mechanical analysis,there were shear displacement and shear stress mutation at the contact surface between the rock layers of the direct roof supporting bolt in the roadway,which results in the tensile failure of the direct roof along the contact area.In addition,the direct roof's The variation of deformation parameters and thickness is an important reason for the stress distribution of bolt.On this basis,through the extraction and analysis of the shear stress value of the anchoring interface of the roof with different thickness,the calculation formula of the critical anchoring length of the direct roof bolt was established,which improves the rationality of the calculation of the supporting length of the direct roof bolt.In view of the corrosion failure of the metal bolt and the decrease of the supporting effect of the direct roof of the tunnel,the applicability of the FRP bolt in the direct roof of the tunnel was tested through the test and numerical simulation.The field support tests of pipe joint anchor and FRP anchor were carried out systematically.The experimental results show that the change of roof thickness has a significant impact on the effect of bolt support,but the effect of FRP bolt support is less sensitive to the change of roof thickness.Through numerical simulation analysis,under the condition of roof thickness change,FRP bolt support can provide more axial tension to squeeze the roof and maintain the stability of the tunnel.Therefore,FRP bolt can replace metal bolt to support in the direct roof of roadway.