Prediction Of Durability Life And Reliability Of Laterally Bearing Capacity Of Pile Foundation In Marine Environment

The reinforced concrete piles exposed to marine environment are vulnerable to chloride erosion.Chloride can penetrate into the concrete of pile foundation by diffusion.When the chloride concentration on the surface of the steel bar reaches the limit concentration,the steel bar begins to rust.With the development of steel corrosion,corrosion products accumulate and expand.When the expansion stress acting on the concrete cover exceeds the tensile strength of the concrete,the concrete cracks and the rigidity of the pile decreases,which leads to the deterioration of the bearing capacity of the pile foundation and causes huge engineering losses.If we do not pay attention to the durability research,the modernization of our country will face all kinds of problems in the future.It is urgent to improve and study the durability of reinforced concrete structure.Therefore,in order to improve the design quality of reinforced concrete structure and prolong the service life of reinforced concrete structure,the reliability of laterally bearing capacity of corroded damaged piles caused by chloride erosion is studied in this paper.1.Based on Fick’s second law,the diffusion model of chloride in reinforced concrete piles is established in column coordinate system and rectangular coordinate system,respectively.The diffusion model is modified by considering the parameters of time,temperature,humidity and stress level,and the time-dependent law of chloride concentration on the surface of steel bar is obtained.Taking the chloride concentration on the surface of the steel bar to reach the limit chloride concentration as the function function,the initial corrosion life of the pile is predicted by the analytical method and reliability method,respectively.In addition,considering the relationship between the initial chloride concentration on the concrete surface and the influence of the diffusion coefficient of chloride with time and the influence of load level on the diffusion coefficient of chloride,the randomness of parameters is simulated.The comprehensive method of forecasting initial corrosion life of pile is proposed by combining analytical method with reliability method.2.The corrosion process of steel bars under chloride erosion is simulated based on Faraday’s law,and the corrosion depth of steel bars is obtained in different service time.The ultimate corrosion depth calculation model is defined.The corrosion depth of steel bars reaches the limit as the function function of concrete cover cracking,and the cracking time is calculated.According to the specification,the calculation model of the stiffness reduction coefficient of pile body is established under the marine environment,and the time variation law of the reduction coefficient of bending stiffness is calculated.3.Based on Winkler foundation model,the reduced bending stiffness is used to modify the model,and the foundation model of corroded damaged pile caused by chloride erosion is obtained.The time-dependent curve of laterally bearing capacity of single pile under deterministic method is obtained by using difference program.The randomness of important parameters is also considered,and the random field model is established by using the center point method to simulate the spatial variability of soil elastic modulus in the vertical direction.The Monte-Carlo simulation method is used to realize the reliability study of laterally bearing capacity of corroded damaged pile.4.The failure probability of corroded damaged piles in marine environment is calculated by Monte-Carlo simulation method.The influence of important parameters on failure probability is analyzed.In addition,under the criterion of displacement failure,the cumulative distribution curve and probability density curve of pile displacement are obtained.The time variation law of the probability density curve of pile displacement with the mean value and variation coefficient of concrete elastic modulus,soil elastic modulus,laterally load and bending moment at pile top are studied.The results show that with the increase of service time,the bending stiffness of the pile gradually decreases,the maximum bending moment of the pile increases,the maximum bending moment point moves upward,and the maximum laterally displacement of the pile increases.Under the two failure criteria,the failure probability of the pile at the initial stage of corrosion remains unchanged,and then increases with the increase of service time.In the same service time,with the increase of bending moment,vertical load and laterally load,the failure probability of pile increases gradually,but the failure probability decreases with the increase of elastic modulus of soil and pile concrete.In addition,the spatial variability of soil elastic modulus decreases with the increase of autocorrelation length.Under the same service time,the failure probability increases with the increase of autocorrelation length.The random variable method is more conservative than the one considering the spatial variability of soil.