| Since the beginning of the 21 st century,with the rapid development of China’s economy,the urbanization process has been accelerating,and more and more megacities and megacities have emerged,but the rapid urbanization process has also brought many problems,one of which is the problem of traffic congestion.From the perspective of the world,the main way for large cities to solve traffic problems is to build a perfect rail transit system,transport super large flow of people,and use all aboveground and underground space to build various urban expressways to dredge vehicle congestion,a city AB road project is one of them.As a result,there are more and more adjacent bridgetunnel projects,among which the construction of SHKP bridges next to existing tunnels is not uncommon.However,during the construction of new projects,it is very likely to cause adverse effects such as cracking and staggering of existing projects,so it is particularly important to judge the safety status of existing tunnel structures simultaneously.This paper takes AB Avenue(crossing the construction section of Metro Line C)as the background,the main line viaduct of AB Avenue diagonally spans Metro Line C,the north side pier of the main line viaduct D16 axis is located on the right side of the left line section of track C line,the middle pier is located between the left line and right line of track C line,the south side pier shares the foundation with the Y0 axis abutment of the left wide bridge,located on the right side of the right line section of track C line,and the horizontal distance between the substructure of the middle pier and the tunnel is only more than 1 meter.Through model testing,theoretical analysis,numerical calculation and monitoring measurement,the stress distribution and displacement response during the construction of bridge and tunnel proximity were explored.The following research results are mainly obtained:(1)The method of indoor soil test is adopted to simulate the construction situation of the bridge pile foundation close to the subway tunnel under the procedure of bridge first and tunnel second.The results of laboratory simulation test show that the maximum settlement of pile top is 6.53 mm and 19.80 mm,respectively,after bridge construction.After tunnel excavation,the basement strains are-2.842e-5 and-4.110e-5,respectively.The overall structure is safe and stable;(2)Based on Mindlin stress solution and Winkler elastic foundation beam formula,theoretical analysis is used to calculate the construction situation of bridge pile foundation in the process of connecting metro tunnel first and then bridge.The results show that during the construction process,the maximum displacement response of the tunnel structure occurs in the tunnel excavation construction step,and its displacement value accounts for about 80% of the total displacement value in the whole construction process.After bridge loading,the arch structure at Z=30 section is the most obvious part of the tunnel structure displacement response.The tunnel settlement of long pile scheme is-1.096 mm,while that of short pile scheme is-0.992 mm.(3)ANSYS Mechanical software was used to conduct finite element simulation of construction schemes under different construction processes of bridge pile foundation close to subway tunnel.The results show that the structural displacement and stress of the short and short pile schemes are within the safety range required by the code.However,the settlement and internal stress of short pile are greater than those of long pile because of the large number of piles and large dead weight load.In addition,the buried depth of pile foundation in the long pile scheme is located below the tunnel.After tunnel excavation,the upward displacement trend will be generated with the surrounding rock and soil mass,which can reduce the settlement caused by the upper load of the bridge to a certain extent and improve the internal stress condition.To sum up,it is recommended to adopt the construction scheme of long pile bridge before tunnel in the actual construction process.(4)On the basis of the finite element simulation in Chapter 4,the finite element simulation of pile foundation isolation measures is carried out for the long pile scheme,and the changes of pile stress and displacement before and after the isolation are analyzed.The results show that the maximum stress difference of pile before and after isolation is9.2%,and the displacement response of arch and arch bottom of tunnel structure is 38.6%and 50.3% respectively.The isolation operation has obvious improvement effect on the whole project.In the actual construction process,if the pile foundation construction is close to the subway tunnel and the buried depth of the bottom of the pile foundation is located under the tunnel arch,it is recommended to adopt the pile isolation operation to release the upper load to the rock mass at the bottom of the pile foundation,which can effectively reduce the displacement response of the tunnel structure.(5)The indoor soil test values,theoretical analytical values and field actual monitoring measurements are compared with the finite element simulation values obtained in Chapter 4.The results show that the results obtained by different methods agree well,and the finite element simulation scheme is safe and reliable. |
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