| The problems of underground water and soil caused by the development of industrialization urgently need to be effectively addressed.Barrier walls are built around contaminated sites to prevent pollutants from entering the underground environment.However,a large amount of waste steel slag generated during industrial production and smelting of steel has accumulated,seriously occupying scarce land resources.Due to the chemical and mineral composition of steel slag being similar to cement and having certain adsorption properties,many domestic and foreign scholars have proposed to replace part of cement with steel slag to increase the resource utilization of waste steel slag.Cement bentonite is a kind of anti pollution barrier wall material with certain strength and low hydraulic conductivity,which has broad prospects in the prevention and remediation of contaminated sites.At the same time,there is relatively little research on introducing steel slag instead of cement into barrier walls in China,expanding the application of steel slag powder in risk prevention and control of contaminated sites.In this thesis,sodium based bentonite,42.5 grade ordinary Portland cement,and steel slag powder produced by Suzhou Jiegao are used to prepare samples,measure the physical properties of the above materials,and systematically study the changes in strength and hydraulic conductivity of steel slag-cement-bentonite barrier materials from a macro and micro perspective.Based on a risk prevention and control project for a mountainous polluted site,Based on indoor test parameters,the construction stability and service life of the barrier wall are evaluated through the slope stability module and the water solute transport module in the numerical analysis software Midas-GTS NX.The research content and conclusions are as follows:（1）The effects of different steel slag substitution rates,bentonite content,and curing age on the strength characteristics of steel slag-cement-bentonite barrier materials were studied using unconfined compressive strength tests and direct shear tests.The test results show that the steel slag substitution rate has a linear relationship with the unconfined compressive strength of the barrier material and an exponential relationship with the cohesion,both of which decrease with the increase of the steel slag substitution rate.The bentonite content has an exponential relationship with unconfined compressive strength and a linear relationship with cohesion,both of which increase with the increase of bentonite content.The unconfined compressive strength of all soil samples at the age of 28d ranges from 58.8 k Pa to 313.3 k Pa,and the unconfined compressive strength at the ages of 7d and 14d has a linear relationship with the strength at 28d.The ultimate strain of barrier materials is basically in the range of 2%to 3%,and the residual strength accounts for about 40 to 60 of the peak strength.By establishing the relationship between the cohesion and unconfined compressive strength of soil samples aged 28 days,it is found that the cohesion and unconfined compressive strength basically meet c=（0.23～0.39）qu,and the unconfined compressive strength can effectively predict the cohesion of steel slag-cement-bentonite barrier materials.（2）The hydraulic conductivity of soil samples with different steel slag replacement rates,bentonite content,and curing age was tested using a variable head hydraulic conductivity test,and the rationality of the results was verified by scanning electron microscope tests.The results show that the hydraulic conductivity coefficient at 28d age is mostly 1×10-6 cm/s～In the range of 1×10-8 cm/s orders of magnitude.The hydraulic conductivity of the steel slag-cement-bentonite material is affected by the replacement ratio of steel slag,the amount of bentonite added,and the age.The replacement ratio of steel slag is between 0 and 50.With the increase of the replacement ratio of steel slag,the hydraulic conductivity of the material continues to improve;Combined with the scanning electron microscope test,it was found that with the increase in the replacement rate of steel slag,needle like substances gradually appeared in the soil sample,alternating with each other,forming a certain spatial structure.With the addition of bentonite（46%～54%）and the aging period（7d～28d）,the hydraulic conductivity of the barrier material gradually increases.This is because as the aging period of bentonite increases,the micro pores of the soil sample gradually become smaller,and the water flow channel decreases,resulting in a decrease in the hydraulic conductivity coefficient.Through the nephogram of the influence of steel slag replacement rate and bentonite content on the hydraulic conductivity coefficient of soil samples at different ages,it is found that the steel slag replacement rate and bentonite content have an exponential relationship with the hydraulic conductivity of the barrier material.（3）Based on the construction project of a barrier wall at the toe of a slope in a mountainous polluted site,the process of trench formation of the barrier wall was simulated using the software Midas-GTS NX slope stability module.The overall stress of the slope,the horizontal displacement and strain of the slot hole during the process of slotting were studied,and the effects of slotting length and mud weight on the horizontal displacement of the slot hole during slotting were studied.The results show that the safety factors of slope stability calculated based on the strength reduction method are 1.61 and 1.53 respectively under the natural state of the slope and after the formation of the groove,indicating that the safety factor of the slope is mainly affected by factors such as stratum,but there may be local instability at the groove hole.By comparing the locations of stress,strain,and maximum horizontal displacement before and after excavation,it is found that due to the squeezing effect of soil on the slot hole after excavation,a stress concentration area appears around the slot hole.The maximum shear strain does not occur at the bottom of the slot hole,but occurs at the junction of poorly soil filled soil layers and strongly weathered andesite.The maximum horizontal displacement of the slot hole gradually decreases with the increase of the slot depth.（4）Establish a numerical model through Hydrus-2D,and select the iron ions with the most excessive multiples in the site as the research object.In the Class IV standard of the Quality Standard for Groundwater（GBT14848-2017）,the iron ion limit value of 2 mg/L is used as the breakdown standard.The width of the barrier wall is set to 0.8 m,and the hydraulic conductivity coefficient is 1.0×10-7 cm/s,after 38.95 years of iron ions breaking through the barrier wall,at the same time,iron ions gradually enter the weathered rock layer under the action of water flow and reach the bottom of the barrier wall to enter the uncontaminated area.The effect of different thickness and hydraulic conductivity coefficient of barrier walls on their service life is studied.The results show that when the design depth is fixed and the hydraulic conductivity coefficient of barrier walls is set to 1.0×10-7 cm/s,the thickness of the barrier wall is between 0.6 m and 0.8 m.Increasing the thickness of the barrier wall can significantly extend the breakdown time.Increasing the width of the barrier wall can hardly extend the breakdown time of the barrier wall,with a thickness of≥0.8 m. |
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