| With the continuous increase of highway mileage,the mileage of tunnels in China has also increased,and the tunnel section has been increasing.Due to the limited conditions of the construction method of large-section tunnels.Based on the finite element numerical simulation software,this paper studies the construction method of the single-hole large-span four-line municipal highway tunnel with the background of the Shiyuan tunnel.By combining the tunnel section and the characteristics of the construction method,combined with the application sequence of the initial support and temporary support,the construction process of each process,the construction process and operation points of the initial support and temporary support are analyzed one by one,and detailed construction steps are formulated.At the same time,through the evaluation of the monitoring and measurement data results of the construction process,the construction quality of the construction method is dynamically feedbacked to ensure the safety of the tunnel construction.The research contents and conclusions of this paper are as follows:(1)The tunnel is excavated by the 9-step method of the well-type double-side guide pit.By observing the displacement variation of the surrounding rock of the tunnel,the variation law of the displacement of the surrounding rock of the tunnel is obtained,which has guiding significance for the tunnel construction.(2)When the surrounding rock is disturbed by excavation,the deformation rate of the surrounding rock is large,but with the passage of time,the deformation rate is gradually reduced until it is stable,and the tunnel is excavated by the 9-step method of the well-type double-side guide pit.The horizontal displacement of the surrounding rock in the left part of the tunnel is greater than the horizontal displacement of the surrounding rock.(3)Prior to tunnel excavation,initial geostress exists in the rock mass due to the self-weight and geological structure of the rock mass.During tunnel excavation,thetunnel excavation relieved the constraint and destroyed the original equilibrium state of the rock mass.The surrounding rock of the tunnel changed from a relatively static state to a changing state,and the surrounding rock force map reached a new equilibrium,and its stress and The strain begins a new movement,and the result of the movement causes the stress of the surrounding rock to reach a new equilibrium again.(4)Through the analysis of the displacement and stress of the surrounding rock of the tunnel excavated by the 9-step method of the well-type double-walled guide pit,it is known that when the tunnel is excavated,the upper part of the tunnel is downward.The displacement of the surrounding rock in this range is reduced due to stress release,and the vertical stress is generated at the bottom of the tunnel.The surrounding rock is released due to the uplift,and the vertical stress of the surrounding rock decreases.The position of the tunnel arch and the side wall is affected by the force of the lower part of the upper surrounding rock and the upward force of the surrounding rock.In this range,the rock mass is squeezed and the vertical stress increases.(5)The monitoring data of the division tunnel in this stage are all within the control range,no large abnormal deformation value,the deformation value does not exceed the warning value,no concrete cracking of the initial support spray layer,bending deformation of the steel arch(grid),Abnormal conditions such as spalling of the roof spray layer.(6)According to the results of third-party monitoring and measurement,the maximum value of tunnel settlement is much smaller than the warning value of tunnel construction,indicating that the tunnel adopts the 9-step construction method of the well-shaped double-side guide pit and the supporting measures for construction.It is reasonable and feasible.During the construction process,the ground settlement and initial support deformation of the tunnel are effectively controlled. |
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