Time-Dependent Scour Depth Prediction And Fragility Analysis Of Bridge Pile Foundation Based On Probabilistic Method

The modern highway and railway transportation network system is related to the people’s livelihood,and the bridge is an important node of the network.During the service period,the bearing and safety performance of the bridge structure are very important to ensure the effective operation of the traffic network.There are many factors that affect the bearing performance and safety performance of bridge structures.In recent years,with the frequent occurrence of extreme rainstorm weather,flood scouring has become one of the main causes of bridge structure damage.How to predict the scour depth of the bridge under the condition of scour and establish the scour vulnerability model is of great significance to evaluate the safety performance of the bridge structure during service.This paper attempts to establish a time-dependent scourng depth prediction method and scouring vulnerability model of bridge pile foundation based on probabilistic hydrological information,which provides an idea for bridge safety performance evaluation under random scouring conditions.The following studies were mainly carried out:(1)This paper classifies the commonly used prediction methods and formulas of local scouring depth of piers,focuses on the time-dependent final scouring calculation method using cohesive soil riverbed,and finally compares the prediction methods of local scouring depth of different piers based on the scouring data of two actual bridge projects.The results show that in the prediction of non-cohesive soil scouring,the maximum scouring depth value obtained by Chinese code is less than the measured value and less than the calculated value of American code under the same conditions,while the maximum scouring depth value obtained by American code is larger than the measured value;In the prediction of cohesive soil scouring,the results obtained by the aging final scouring depth prediction method are closer to the measured results than the predicted value of the maximum scouring depth,and this method can not only obtain the maximum scouring depth value,but also reflect the development process of the scouring depth with the service time of the bridge.(2)A program for predicting scour depth under complex conditions is developed based on "SRICOS equation".Taking an actual bridge project as the background and considering the uncertainty of hydrological information,the Monte Carlo simulation technology is used to statistically analyze the distribution law of pile foundation scour depth prediction during bridge service.The results show that the predicted scour depth increases with time,and the standard deviation of the predicted result in the scour range of non-cohesive soil is always larger than that in the complex soil layer,and the former shows a downward trend,while the latter fluctuates within a certain range.The risk assessment curve based on the predicted scour depth increased rapidly in the first 30 years and slowed down in the later stage.(3)Considering the uncertainty of bridge pile foundation bearing capacity and load action effect,a time-varying safety performance evaluation method of bridge pile foundation based on scouring depth parameters is constructed.The distribution characteristics of bridge pile foundation bearing capacity at a specific time point are calculated by Monte Carlo simulation technology,and then the failure probability of pile foundation structure at that specific time point is judged,the time-varying vulnerability model of bridge pile foundation during service is obtained by time accumulation of time point failure probability.The results show that the risk of scouring failure of bridge pile foundation increases with the increase of bridge service time,and the curve can be directly used to evaluate the loss of scouring disaster.