Study on Roof Caving Mechanism and Support Scheme Optimization of Tunnels in Thin-bedded Rock Mass
With the Caojiading Tunnel on Linzi-Linyi Expressway in Shandong being used as an example in this study,the three-dimensional discrete element numerical calculation software 3DEC is used to create the analysis model,in order to investigate the roof caving mechanism of a tunnel in thin-bedded rock mass.Through roof separa-tion monitoring and plastic zone analysis of the crown rock mass,it is determined that the root cause of crown roof caving is the fact that the original rockbolt support system fails to effectively control the roof caving height.On this basis,the anchor cable support scheme is proposed and the support parameters are optimized and analyzed.3 variables are analyzed,including various anchor cable lengths,number of roof anchor cables and side wall rockbolt quantity ratio.According to the numerical calculation,the optimized anchor cable support scheme is selected,where there are 5 anchor cables which are 5.5 m long in the scope of the roof and the side wall rockbolt quantity ratio is 0.5.A tunnel section with the risk of roof caving is selected to conduct the anchor cable support test.According to analysis of the monitoring data,the average axial force of anchor cable at the tested section is increased by 65.1%,31%and 8.5%at the position below the spandrel,at the position above the spandrel and at the crown as compared with the average axial force of rockbolt at the same positions in the common section.This indicates that anchor cable support system can control crown roof caving more effectively than rockbolt support system.
Thin-bedded rock massRoof caving disaster3DEC numerical simulationAnchor cable supportSite monitoring
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