Deterioration Mechanism And Life Prediction Of Tunnel Lining Under Multiple Factors Based On Bayesian Model Averaging

Under the action of carbon dioxide,chloride ions and other factors,the tunnel lining will cause corrosion of the internal steel bars of the structure,which will lead to varying degrees of structural deterioration,making the tunnel lining unable to complete its service within the design period.In the past,life prediction relied on the initial state of the structure and used a single formula for prediction,and the results were often inaccurate and conservative.In addition,at present,it is difficult to accurately grasp the tunnel life in which form to predict the tunnel life and how to use the existing monitoring information to obtain more accurate values.In this paper,on the basis of the influence of carbonization depth and chloride ion concentration on the corrosion of steel bars,the functional functions of the flexural bearing capacity of the normal section of the steel bar after corrosion is established,and the expected life of the tunnel is determined through reliability calculations.In addition,this study uses the Bayesian model averaging method,combined with the existing detection information provides a reliable and efficient method for predicting the life of the tunnel,and then compares the prediction results of the case with the detection information,and the model after the Bayesian model average can improve the accuracy of the prediction of the tunnel life,as follows:1.The mechanism of tunnel lining deterioration is analyzed,and a lining deterioration model considering steel corrosion is established.In order to avoid over-conservative life prediction,the corrosion state of the lining steel bar under different factors of corrosion,the change of steel bar strength after steel bar corrosion and the change of concrete strength with time were studied,and the time-varying flexural capacity model of the normal section after corrosion was established.2.The prediction of the life of the tunnel lining is completed by establishing the functional function to calculate the reliability.The functional function of the corrosion of the steel bar under carbonation and chloride ion erosion,the functional function of the flexural bearing capacity of the normal section after the corrosion of the steel bar,and the time-varying concrete strength change and Corrosion causes changes in the strength of steel bars,and a sensitivity analysis is performed on the model parameters in the function function,and the uncertainty of the model is included in the calculation process.3.Based on the Bayesian model averaging method,the weighted average of the existing calculation models is carried out respectively.For the corrosion model,the carbonation depth model average and the chloride ion concentration model average are considered;for the bearing capacity model,the time-varying concrete strength and steel bar strength model average are considered,and the weight of the model is updated based on the existing observation values to obtain a model that is closer to the real value,and use the error evaluation to judge the existing model and the Bayesian updated model,so as to realize the accurate grasp of the tunnel life.Taking a tunnel in South Korea as an example,the theoretical calculation model is used to evaluate the tunnel life under different influencing factors,and based on the detection information,the update and prediction of the tunnel life is realized.The results show that the inner steel bars of the tunnel lining will not be corroded due to carbonization within the design service life,and the outer steel bars of the lining will be corroded in the 35 th year because the chloride ion concentration at the position of the protective layer reaches the threshold value.When the limit state of the flexural capacity is taken as the standard,the tunnel will fail to meet the design service life in the 97 th year due to insufficient bearing capacity due to the corrosion of the outer reinforcement of the lining.Therefore,it is necessary to strengthen the monitoring of tunnels in actual engineering in order to carry out preventive maintenance on tunnels.