Study On Sulfate Ion Diffusion Mechanism Of Cantilever Anti-Slide Pile Under Sulfate Attack Environment

Our country is vast and there are a large number of saline land areas.The anti-slip piles built in these areas have been subjected to sulfate erosion for many years,which has also led to a rapid decline in the bearing capacity of the anti-slip piles and ultimately threatened the safety of people’s lives and property in the area.Ensuring that anti-slip pile structures in sulfate-containing areas can effectively achieve their intended functions over the design life has become an urgent problem to be solved.Therefore,the study of the sulfate ion diffusion mechanism of the pile body under sulfate erosion is particularly important,which provides a very important guidance for the design and monitoring of the anti-slip pile in the salt lake area.Through indoor acceleration experiments,the sulfate ion content at different depths of the pile body changes with the concentration and erosion age of the erosion solution after the cantilever anti-slip pile is subjected to sulfate erosion,and finally the diffusion mechanism of sulfate ions in the cantilever anti-slip pile is comprehensively analyzed through the results of numerical simulation.The main research contents and conclusions are as follows:（1）The cube specimens are soaked in different solutions of water,5%sodium sulfate and 10%sodium sulfate3,and the cube specimens are drilled,sliced,ground and titrated after erosion for 30d,60d and 90d,and the sulfate ion content of the cube specimens at different depths is recorded.The effect of the size of the erosion solution concentration and the length of the erosion age on the sulfate ion content at different depths of the cube specimens was studied.（2）Orthogonal tests of 5%and 10%of different solution concentrations and erosion ages of 30d,60d and 90d were carried out by the experimental device of load-sulfate coupling erosion of cantilever anti-slide pile.By analyzing the SO₄^2-content of cantilever anti-slide pile,it is found that the higher the concentration of erosion solution and the longer the erosion age,the higher the SO₄^2-content of cantilever anti-slide pile.In addition,SO₄^2-is mainly concentrated on the surface of cantilever anti-slide pile,and the content of SO₄^2-decreases rapidly with the increase of depth.After 30 days,60 days and 90 days of sulfate erosion,the SO₄^2-content in different depths of cantilever anti-slide pile was measured respectively.It was found that when the erosion age increased from 30 days to 60 days,the growth of SO₄^2-content in cantilever anti-slide pile appeared a plateau.Combined with the mechanism of sulfate erosion,the analysis of the reason for the plateau stage is that the gypsum and ettringite produced by erosion inside the concrete in the first 30 days of erosion filled the pores inside the concrete,reducing the porosity of the concrete and reducing the rate of sulfate erosion in a short time.Meanwhile,the higher the concentration of the erosion solution,the less significant the plateau stage.（3）The analysis of SO₄^2-content in different sections of cantilever anti-slide pile shows that the SO₄^2-content in cantilever anti-slide pile changes with the change of section.When the section of cantilever anti-slide pile changes from J₁ to J₄,the SO₄^2-content in the pile decreases gradually,and when the section changes from J₄ to J₆,the SO₄^2-content increases gradually.The SO₄^2-content in J₆ section is the largest compared with the other 5 sections.In J₁-J₄ section,the compression stress is smaller,which makes the concrete more compact.The SO₄^2-content in the cantilever anti-slide pile after erosion is lower than that in the concrete specimen.The compressive stress at J₆ section is larger and micro-cracks appear inside the concrete,so the SO₄^2-content in the cantilever anti-slide pile is higher than that in the concrete specimen.（4）After consulting relevant literature,we simulated the sulfate erosion cube specimen in COMSOL software to study the influence of sulfate age and sulfate concentration on the depth and range of erosion.Finally,it is found that the numerical simulation results are basically consistent with the experimental results.By studying the maximum erosion depth of SO₄^2-under the action of compressive stress-sulfate coupling,the diffusion law of SO₄^2-is obtained when concrete is subjected to different compressive stress levels.With the increase of compressive stress,the resistance of concrete structure to sulfate attack first increases and then decreases.