Numerical Analysis Of Long-term Working Performance Of Helical Anchor For Transmission Line In Cold Regions

In recent years,with the rapid development of China’s economy,more and more engineering projects have started construction in the northern cold regions,and the transmission network has also expanded.The deformation of soil in seasonal frozen soil areas is significantly affected by changes in external temperature.The frost heaving and thawing settlement of soil can affect the stability of transmission line foundations,and in severe cases,the foundation may fail due to pullout.Therefore,the analysis of the stability against frost uplift and the prevention and control of frost heave disasters in seasonal frozen areas are key issues to be solved in engineering construction.Helical anchor foundation is an effective foundation type for frost resistance of transmission lines in cold regions due to its simple manufacturing,convenient construction,low environmental disturbance,and good anti uplift performance.It has broad application prospects.However,there is currently limited research on the helical anchor foundation of transmission lines in cold regions,and there is a lack of normative guidance.This article focuses on the deformation and stability of helical anchor foundations under freeze-thaw cycles in seasonal frozen areas.Numerical simulation is conducted using ABAQUS finite element software to analyze the temperature changes in soil,freezing depth development,anchor soil contact stress,anchor top displacement,and soil surface displacement development patterns during multiple freeze-thaw processes under typical seasonal frozen area temperature conditions.Furthermore,temperature conditions,anchor top loading conditions,and the geometric form and size of helical anchors are changed,Explore its impact on the displacement and force transmission mechanism of foundation freezing and pulling.The main research work and related achievements are as follows:(1)Based on the ABAQUS finite element numerical analysis platform,a soil helical anchor interaction analysis model considering the freeze-thaw characteristics of soil is established.Considering the characteristics of the contact surface between the anchor and cohesive soil,especially during the freezing process,a bond damage friction coupled contact surface model is used to describe it,and compared with the friction model.The rationality and reliability of the modeling method,soil model and contact surface model are verified by comparing with the soil temperature distribution obtained from the helical anchor foundation freezing model test and the final freezing displacement of the foundation.Laying the foundation for modeling and analysis of subsequent actual dimensions and loading conditions.(2)Based on the high and low temperature values of a typical seasonal frozen soil area in Northeast China,the cosine function is used to simulate temperature changes within a year.Under surface temperature loading,analyze the development and changes of temperature in the soil,including the development process of freezing depth,freezing depth,freezing displacement,and lateral shear stress of the foundation.The differences in the performance of helical anchor and straight pile foundation types during freeze-thaw cycles were mainly discussed.(3)To analyze the impact of temperature conditions,basic deformation and stress analysis is conducted by changing the extreme and average values of loading temperature.The results show that only when the average loading temperature is 0 ℃,there is a significant accumulation of freeze-thaw displacement in the screw anchor foundation under multiple freeze-thaw cycles,and its stress characteristics are also different.To analyze the influence of anchor loading conditions,a uplift model of screw anchor foundation in unfrozen soil was established and the ultimate uplift bearing capacity of the foundation was calculated.The frozen uplift displacement and stress characteristics of the foundation under 1/5,1/3,1/2 ultimate uplift load were studied;As the level of uplift load increases,the initial uplift displacement of the foundation increases,and the extreme stress around the pile also increases.(4)The geometric characteristics of helical anchors are important factors affecting their stress and deformation.Establish a basic model with different number of anchor pieces,spacing between anchor pieces,and diameter of anchor rods.By comparing and analyzing the development of freeze-drawing displacement and shear stress changes,discuss the influence of basic geometric dimensions on its pull-out performance.