Numerical Simulation And Analysis Of The Impact Of Crossing Construction With Mining Method

With the continuous development of underground engineering,the number of tunnel proximity construction projects has increased sharply,and more and more tunnel construction has to be carried out in the vicinity of existing tunnels and underground engineering.In the process of construction,the new tunnel will impact the existing tunnel to some extent.It is of great significance and practical value to ensure the safety and serviceability of the existing tunnel structure by analyzing and studying the construction of the new tunnel,and finding out the influence on existing tunnels,so as to provide reference for the control method of the influence.In this paper,the engineering project of Zhuhai Urban-Airport Intercity Railway tunnel crossing the Dahengqin mountain double-line tunnel is taken as the research object.By using ABAQUS to build a three-dimensional tunnel model,the impact of the excavation of the upper tunnel on the deformation and vibration of the existing tunnel was analyzed.Furthermore,the corresponding reinforcement measures are taken to analyze the effectiveness of the reinforcement measures.Its main contents and conclusions are as follows:1.Due to the complexity of the strata in which the tunnel is located,the strata of different soil interlaced with the existing tunnel and the newly built overpass tunnel.The traditional stratification method requires irregular segmentation according to the soil layers,which will increase the number of distorted elements and decrease the mesh quality,thus affecting the calculation accuracy.For this reason,a new method of material assignment is adopted in this paper.The field variables are assigned to the properties of soil materials for calculation,and the method is compared with the traditional method of material assignment.The results show that the new method is reliable and accurate,which reduces the workload in the process of model creation and solves the problems of mesh distortion caused by model segmentation.2.The commonly used tunneling method is mining method.In this paper,two methods of tunneling through the tunnel are used.One is to use the Benching-Tunneling method for mechanical excavation and the static analysis step is used for analysis.The other is the full section Drilling-Blasting method,which adopts the dynamic analysis step and the static analysis step.The calculations demonstrate that,if the Benching-Tunneling method is adopted to construct the tunnel,the existing tunnel is uplifted in the area below the tunnel,and its maximum vertical deformation value is less than the limit value required by the project.However,when Drilling-Blasting method is adopted for excavation,the maximum vibration velocity caused by each section does not exceed the limit value,so the existing tunnel structure is in a safe state.The results show that the mining method can be used to excavate the tunnel without safety problems.3.In order to reduce the impact of the up-crossing tunnel on the existing tunnel in the excavation process,in this paper,relevant strengthening and vibration reduction measures are adopted,and some influencing factors of these measures are analyzed and discussed.In order to reduce the deformation,the reinforcement method is adopted in this paper.The reinforcement dimensions in the z direction and y direction were taken as variables.The results showed that with the expansion of the reinforcement range,the uplift degree of the existing tunnel became smaller and the reinforcement effect was better.As for the height change of the reinforcement,it has a certain influence on the reinforcement effect,but it is less obvious than the reinforcement range in the direction of z.In order to reduce the vibration velocity,this paper reduces the vibration effect of tunnel excavation on the existing tunnel by reducing the tunneling footage.The results show that: after reducing the footage to half of the original,the vibration velocity of each point on the monitoring section decreases by about 73%,which indicates that reducing the footage has an obvious effect on reducing the vibration velocity of the existing tunnel.