Study On Long Term Stability Of Diversion Tunnel Lining Under Sulfate Erosion

Concrete structures existing in the underground are often subjected to high formation stress,high surrounding rock pressure,high osmotic pressure,and various physical and chemical functions.Studying the long-term stability of underground concrete in a multi-field coupled environment is one of the most basic scientific research topics in underground engineering such as hydraulic tunnels,subway tunnels,and cross-river(sea)tunnels.It has very important practical significance.In a complex water environment,underground concrete will gradually deteriorate in performance due to the effects of osmotic pressure,acidic substances,aggressive ions,and carbonization,resulting in durability failure.Therefore,studying the long-term stability of diversion tunnel lining under sulfate attack has important theoretical significance and value for hydraulic tunnel engineering and other underground projects.In this paper,cement mortar is taken as the research object,mainly to study the change rule of the microstructure and macroscopic mechanical behavior of cement mortar with erosion time under the condition of sulfate erosion.The cement mortar samples after curing in air and soaking in sulphate were tested respectively.Microscopic properties(SEM,CT scan)and macro-mechanics(uniaxial,splitting tensile,wave velocity,porosity,permeability)and numerical simulation software were used to analyze the samples before and after erosion.The analysis shows that:(1)The permeability coefficient of the sample is closely related to the confining pressure.With the increase of confining pressure,the permeability coefficient decreases gradually,and the rate and degree of decrease of permeability coefficient of corroded and unetched specimens are different.The permeability coefficient of corroded specimen is more sensitive to the change of low confining pressure(5MPa-20MPa).Under high confining pressure(20MPa-30MPa),the pores of the eroded sample collapsed,the internal structure was destroyed,and the rate of decrease of permeability coefficient was obviously weakened,leading to the fact that the permeability coefficient was lower than that of the non-eroded sample.(2)The SEM and CT scan showed that the microstructure of the sample changed.The wave velocity of the sample in the erosion group was obviously lower than that in the non-erosion group,but the porosity was higher than that of the non-erosion group.(3)Compared with the non-eroded group,the macroscopic mechanical properties of the sample caused by sulfate attack decreased.The splitting tensile test was more sensitive to the damage caused by sulfate attack than the uniaxial compression test.(4)Using the numerical simulation software COMSOL to simulate the related sample results,the conclusions obtained are almost the same as the experimental ones,which are basically consistent.The relevant experimental results may provide some references for the long-term stability of the underground concrete structures in the high sulfate area.