Research On Efficient Construction Of Weak Surrounding Rock Section Of Tongzi Tunnel

For super-large cross-section highway tunnels with more than three lanes,when crossing weak and broken surrounding rock,the traditional double-side pilot tunnel method has complicated construction steps,its construction efficiency is often low,and the construction period is long,so it is difficult to meet the construction period requirements for projects with tight construction period requirements.Three-step method and CD method have greatly reduced construction steps,and their construction efficiency is higher than that of double-side-wall pilot tunnel method.Therefore,it has certain practical significance to adopt efficient construction methods to improve the tunnel construction efficiency in weak surrounding rock section.Relying on Guizhou Province's major science and technology project Research and Demonstration of Key Technologies for Efficient Construction and Intelligent Operation and Maintenance of Super-long and Large-span Highway Tunnels in Complex Geology,this paper studies the mechanical behavior of Tongzi Tunnel in weak surrounding rock section with three steps method and CD method.The main work is as follows:1.A set of model test bench which can be used to simulate 3D tunnel excavation is designed and manufactured.The internal clearance dimensions of the bench are 2m long,1.2m high and 0.8m thick.The bench has the advantages of quick filling and unloading,convenient loading and visual test process.Based on the model bench,a method of measuring vault settlement with dial indicator is designed,which creatively solves the problem of difficulty in measuring vault settlement.2.According to the geological data of the weak surrounding rock section of Tongzi Tunnel and referring to Code for Design of Highway Tunnels(JTG3370.1-2018),the similarity ratio of 1:50 is adopted to prepare similar materials for simulating the surrounding rock of the tunnel.3.Carry out 3D excavation model test of Tongzi Tunnel in weak surrounding rock section.The similar model tests of three steps method,CD method and double side-wall pilot tunnel method are studied,and the mechanical responses of tunnels with different step height excavation schemes are analyzed.The optimal step height of three-step method and CD method are studied.Through the similar model test,it is shown that the construction efficiency can be increased by 50% when the three-step method is adopted,and by 35% when the CD method is adopted,compared with the double-side heading method.4.Using numerical simulation software,the tunnel analysis model is established to analyze the stress and strain of surrounding rock and study the change law of supporting internal force when different heights change.5.The field construction practice of Tongzi Tunnel shows that the construction efficiency can be greatly improved by adopting three steps method and CD method in the weak surrounding rock section of Tongzi Tunnel.