Study On Construction Mechanics Behavior And Influence Zone In Newly-built Adjacent Tunnels On Both Sides Of Existing Tunnels

The national traffic network has been developing continuously,and the dense transportation network has brought about a large number of mountain tunnels close construction phenomenon.Tunnel near the railway,pile,close to the existing tunnel situation has occurred.Due to the complex structure of the tunnel,the uncertain soil,excavation will disturb the surrounding soil,and then have an impact on the existing structure,even will lead to the occurrence of disasters.At the same time,the tunneling problem has always been a hot topic in the tunnel engineering field.This paper is based on the newly built tunnel project on both sides of the existing tunnels of Pu Mei Railway.For the actual situation of the project,we study on the adjacent project by the way of the data research,and numerical simulation.The main contents and achievements of this paper are as follows:(1)This paper summarizes the relevant theories of adjacent construction at home and abroad,and studies the tunnel excavation with different mechanical models and different stress analysis methods under different conditions.We proposes the concept of equivalent diameter of multi-tunnel and revise the geometric adjacent degree to adapt to multiple tunnels adjacent to a structure of the situation at the same time,Which provides theoretical support for the adjacent tunneling of double newly built tunnels.(2)Analysis of recent engineering design information,this paper use the finite element software MIDAS GTS NX to analyze the actual situation of the adjacent project,and establish the adjacent form of different structures and different excavation order models.The excavation mechanics behavior is studied by means of the stress of the surrounding rock,the displacement and the internal force of the structure.According to different changes in the law,the optimal excavation order is founded,which provides some technical support for the construction.(3)We summarize six kinds of criteria of adjacent influence degree,and determine the structural displacement criterion and the existing structural reliability criterion according to the actual situation,then carry out the study of adjacent partition.The influence subzone,based on the analysis of the influence of different distance on the existing structures(50 kinds of conditions)and combined with the identified structural displacement and structural reliability criteria,is determined according to the adjacent degree formula.(4)By summarizing the relevant information and the related engineering examples,the dissertation defines the processes to solve the adjacent construction problems.It is suggested that different construction countermeasures should be adopted for different adjacent impacts.We propose a set of assessment models,including the improvement coefficient of the various measures and the difficulty of funds,technology and construction.The coefficient of use is evaluated,and according to this coefficient,the construction strategy is selected,which will play a supporting role in the follow-up construction selection.