Research On Impact Of Shield Tunnel Crossing Existing Bridges And Countermeasures Of Excavation Safety Based On Pile Foundation Underpinning

In recent years,the scale of metro construction has been rapidly expanded in China.It is common for metro shield tunnels to cross under pile foundations of existing buildings or structures in urban flourishing area.What’s worse,some pile foundations invade the boundary of shield tunnels.Especially for projects where shield tunnels have to cross under existing bridges,it is necessary to solve such problems.Since with the large self-weight of the bridge structure and large dynamic load,bridges are vulnerable to safety accidents due to tunnel excavation.The study is based on the project of the tunnel between Futian Port Station and Fumin Station of Shenzhen Metro Line 10 across the bridge in Fukuda Bonded Zone.Many methods including numerical simulation and analysis of measured data is adopted to carry out the study.Seeing the interaction between bridge and tunnel caused by the construction of shield tunnels beneath existing bridges,a series of mechanical responses caused by engineering implementation are analyzed.Technology for controlling this effect and countermeasures of excavation safety are researched in this paper.The main research contents and conclusions are shown as followed:1.Construction process of shield tunnel beneath existing bridge without any control technology is simulated utilizing numerical simulation.The phenomenon has been revealed that bridges and tunnels interact greatly according to the analysis of mechanical response of bridge and tunnel structures and it is difficult to ensure safety in construction process.2.The advantages of active underpinning of pile foundations are analyzed to control the interaction caused by construction of shield tunnel beneath existing bridges.The construction process and the key points of improved construction method of active underpinning of pile foundations are summarized comprehensively.The improved construction method of active underpinning of pile foundations are simulated to demonstrate the safety and suitability by numerical simulation.3.Construction process of shield tunnel beneath existing bridge after the pile foundations are underpinned is simulated by numerical simulation.The result thatactive underpinning of pile foundations can effectively control interaction between bridge and tunnel to ensure construction safety has been proved.4.Based on the risk factors in the construction process,the construction control technology of shield tunnel crossing existing bridges is further improved from the perspective of countermeasures of excavation safety,with deformation monitoring data of the bridge structure and the construction parameters of the shield taken into consideration.