The Assessment Of Qiansimen Bridge Approach’s Safety Influcened By The Adiacent Foundation Pit Excavation

With the development of urbanization and urban construction,underground spaceas gradually been developed and utilized fully,especially in the mountain city asChongqing. The phenomenon that deep excavations are close to the bridges and stationsof light rail way makes appearances frequently, with the trend of urban trafficthree-dimensional. And it is obvious that some risks will be exposed,as the balancebetween adjacent bridges and the stations been destabilized due to the deep excavation.So, it’s important to strengthen the risk management of urban bridges adjacent to deepfoundation pit.In the engineering background of Qiansimen Bridge in Chongqing, this paperexamines the risks of the bridge influenced by the adjacent Yueyang deepexcavation.The main contents of this paper are as follows:①The system of risk index is the key and basis of the bridge risk identificationand assessment.Based on this,this paper summarizes the risk index system of bridge andexcavation engineering from the perspective of design, construction, structure,environment,business administration and so on.Then according to the characteristic ofQiansimen Bridge Approach and Yueyang foundation pit engineering,building the risksystem of Qiansimen Bridge Approach,including6first level risk indexes such as slopesupporting design,foundation pit construction and16second level risk indexes such asfirst order support,set back multi-stage support, excavation sequence.②A risk assessment method that combine the identification with checkout of keyrisk factor is put forward and applied to the risk assessment of Qiansimen BridgeApproach. Based on the entropy theory,we can give a evaluation matrix according toweights of every risk index determined by expert scoring,and establish model of riskidentification.Then calculate the entropy value of every risk index to recognize the keyrisk index. The example of Qiansimen Bridge Approach shows that the key risk index isslope supporting design. Based on the analysis of mechanism abaout bridge from thefoundation pit,choose the displacement and settlemen as the Qiansimen BridgeApproach analysis indicators.To first-order support and setback multi-stage support,thepaper analyze displacement and settlement of Qiansimen Bridge Approach and rampwith technology of ABAQUS analysis.The result shows that the key risk index isacceptable.Based on both supporting program,Further comparative analysis of Qiansimen Bridge Approach displacement values and the settlement value, the resultshows that setback multi-stage support more reasonable than the first-order supportprogram③The purpose of risk assessment is preventing accidents,more specifically,Based on the Risk control system of Qiansimen Bridge Approach,proposed riskmonitoring as Qiansimen Bridge Approach risk pre-control means.Setting up threelevels warning system of displacement and settlement of Qiansimen bridge accordingto alarm, early warning and control values based on the risk assessment results. What’smore,the monitoring of18displacement monitoring points from Z01to Z18and18settlement monitoring points from X01to X18can achieve the risk pre-control ofQiansimen Bridge Approach. Based on spatial location relationship of bridge approach and foundation pit, the paper analyze the data of key monitoring points including X06~X08,X10~X12,Z06~Z08,Z10~Z12,etc which being elected.The examination shows:neither the displacement value nor settlement value of Qiansimen Bridge Approachand ramp excess the alarm value,risk can be controlled.The study about the risk assessment of Qiansimen Bridge Approach is adaptableand offer experience for other similar engineering.It has theoretical value andapplication meaning. In the finality,the problems requiring further studies werediscussed.