Research On Safety Control Technology Of Subway Underpass Expressway Overpass

With the rapid development of urbanization in China,road traffic congestion is becoming more and more serious,and accelerating the construction of urban subway is an effective solution to this problem.In urban metro construction,when using space resources,metro shield construction will inevitably pass through the existing surrounding structures,and the construction process will change the stress state of surrounding soil,thus affecting the surrounding structures and their own safety.Taking the Shield Tunnel from Gaopeng Avenue to Shenxianshu Section of Chengdu Metro Line 7 through Chengya High Speed Overpass as the engineering background,and combining with the methods of field geological investigation,technical data investigation,field monitoring and finite element numerical simulation,this paper studies the influence rules of shield tunnels on ground settlement,horizontal displacement and vertical settlement of pile foundation of overpass when Metro Shield Tunnels cross Expressway overpass.Furthermore,a set of safety control technology for metro shield underpass Expressway Overpass is summarized.The main work is as follows:(1)Based on the research status of the influence of metro shield construction on surrounding soil and pile foundation at home and abroad,the influence mechanism of metro shield construction on surrounding buildings is analyzed,and the influencing factors of pile foundation and ground deformation of overpass are analyzed.(2)Based on the section of Chengdu Metro Line 7,through on-site monitoring,the monitoring data show that the settlement trough of the vertical tunnel section on the surface is consistent with the normal distribution curve,and the shield tunneling affects the surrounding soil in a range of about 2-3 times the diameter of the shield tunneling.Through drawing settlement curve along the tunnel direction section monitoring points,it is found that the ground surface first heaves up and then settles during the shield tunneling process,and the settlement rate increases after the shield tail leaves.The surface subsidence curve drawn by monitoring points in vertical tunnel direction shows that the distribution of surface subsidence trough is normal curve,which basically coincides with the results of Peck formula.The influence of shield construction on the deformation of pile foundation on the right side of overpass is greater than that on the left side,mainly in the horizontal direction.(3)Through the finite element simulation software Midas/GTS NX,the dynamic and static loads of a certain frequency are applied to the overpass deck respectively.The deformation laws of the ground surface and the overpass pile foundation under the two kinds of loads are simulated and analyzed.By comparing the monitoring data,it is found that the deformation laws of the pile foundation under the dynamic and static loads are approximately the same as the field monitoring data,which verifies that the numerical simulation has certain reference value.The simulation results show that the values under dynamic loads are closer to the field monitoring data.On the premise of dynamic load on bridge deck,the deformation law of pile foundation of overpass with three different shield thrust forces of 100 kpa,200 kpa and 300 kpa is simulated and analyzed.Under the condition of controlling Shield Thrust and other parameters unchanged,the deformation law of pile foundation of overpass under three grouting pressures of 150 kpa,250 kpa and 350 kpa is analyzed.It is found that the shield thrust has a significant effect on the level of pile foundation.Especially along the direction of shield tunneling,the increase of grouting pressure can reduce ground settlement,but increase the horizontal deformation of pile foundation.(4)By collecting on-site geological survey and construction data,combined with the numerical simulation results,the safety driving control measures for metro shield section construction under Chengya Expressway overpass are put forward.