| Tunnel excavation and surrounding rock support method are always the core problems in tunnel engineering.New austrian tunneling method has been applied in tunnel support system with its distinctive advantages for nearly a century.Bolt and concrete play a significant role in tunnel surrounding rock support.The system bolt is widely used in the tunnel surrounding rock support,which costs a lot of cost and time,in recent years,whether to use the system bolt or not and how to use it in terms of the surrounding rock of class III and IV tunnels,there have been different opinions and controversies in academic circles.Taking the Longquankou super long tunnel in Beijing Chongli expressway of Beijing Olympic Winter Games' key engineering as an example,aiming at the surrounding rock of class III and class IV of the tunnel,the block discrete numerical calculation method is used to carry out the numerical simulation of the use and use method of the system bolt for the surrounding rock of different grades of the Longquankou super long tunnel,to optimize the design of the surrounding rock bolt support method,and combined with the surrounding rock monitoring and measurement,the optimization effect of the use method of the system bolt is verified.The main research contents are as follows:(1)In the surrounding rock with class ?,the whole section excavation is adopted.As for the arrangement of system bolts.Four different layout schemes,including original design scheme,arch layout system bolt,side wall layout system bolt and no-system bolt,were selected,comprehensively compared the settlement displacement of arch,convergence displacement of arch waist,axial force of system bolt,surrounding rock stress,stress on concrete and plastic zone of the tunnel under four working conditions.Results show that canceling the use of system bolts is not obvious in changes of the tunnel's overall stability,so system bolts near the surrounding rock with class ? in Longquankou tunnel can be canceled.(2)For the upper and lower step method of the IV grade surrounding rock of Longquankou super long tunnel,3DEC block discrete numerical simulation software is used to optimize the layout of the system bolt.(1)As for the arrangement of system bolts.Three kinds of system bolts,including the original design scheme,system bolt only retaining the larger angle with the structural surface and no-system bolts,were selected,comprehensively compared with the settlement displacement of the tunnel vault,the convergent displacement of the arch waist,the axial force of the system anchor,the stress of surrounding rocks and the stress of concrete under three working conditions.The results show that it has little effect on the overall stability of the tunnel to cancel the bolt which has a small angle with the structural surface and to keepthe bolt which has a large angle with the structural surface.(2)As for the use of feet-lock bolt.In pursuit of best supporting effect,different lock foot bolt insertion angle(0°?15°?30°?45°)and different anchor length(3.5 m,4.5 m,5.5 m)are chosen.In pairs,there are 12 working conditions.The settlement displacement of the arch roof,the convergent displacement of the arch waist and the axial force of feet-lock bolt are compared.The results show that the optimal insertion angle and length of feet-lock bolt are respectively 15°and 4.5m.(3)The optimization scheme is applied in the site construction,combined with the monitoring and measurement of the tunnel surrounding rock,and the tunnel surrounding rock of the optimized section is stable in the construction process,without construction accidents and construction disasters,which verifies the optimization effect of system bolt's use method.It saves the construction period of Longquankou super long tunnel for nearly ten days and tens of thousands of yuan in cost.Through the optimization analysis of bolt parameters in Longquankou super long tunnel,this paper is hoping to provide relevant reference for the bolt support research in the future tunnel engineering. |
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