Research On Reliability-Based Durability Prediction Of Transmission Line Foundation In Saline Soil

As an important load bearing part of transmission structure, foundation under saline soil is usually affected by many factors, such as corrosion, stress, etc.. So the service life does not satisfy the requirements for the intended use since the durability failure, which will threat to the safe operation of the whole transmission lines. In this thesis, a specialized durability prediction model of transmission line foundation under saline soil was performed based on the Fick’s Second Diffusion Law. Then, considering the uncertainty of the parameters from foundation structural materials, external environment and construction, the durability limit-state function of foundation was established based on reliability theory. Finally, the reliability and sensitivity analysis of an inclined column foundation of ±800 kV UHV DC transmission line from Hami South to Zhengzhou was completed, which provided basics for the durability design of transmission line foundation in saline soil.Starting from the corrosion mechanism of reinforced concrete, and considering the factors such as the tensile and compression load, time variation of diffusion coefficient, foundation concrete materials, environment and construction, etc., this paper established a specialized durability prediction model of transmission line foundation under saline soil based on the Fick’s Second Diffusion Law.Then, the thesis established the durability limit-state function of foundation based on reliability theory, and achieved reliability indexes calculation of target durability with the Second Order Reliability Method(SORM). And the effect of various durability statistical parameters on durability failure probability distribution of the inclined column foundation above was studied, such as thickness of foundation, concrete water-cement ratio, critical chloride ion concentration, curing time, annual average temperature, and so on.For the durability reliability sensitivity analysis of transmission line foundation under saline soil conditions, the thesis defined relative mean and variance of sensitivity factors to describe the durability reliability sensitivity of foundation by basic sensitivity factors, and studied the durability sensitivity of the inclined column foundation above. Result shows that the environmental relative humidity, concrete water-cement ratio, load and crack factor are more sensitive, which must be given due attention in the durability design of foundation. While, for those low sensitivity factors, such as initial chloride ion concentration in concrete, surface chloride ion concentration of foundation, chloride ion binding capacity, environmental temperature and slag amount, are proposed to be considered as the certainty in the durability design of foundation to reduce the dimension of the space of random variables, and improve computational efficiency of durability reliability analysis on the transmission line foundation under saline soil conditions.