| Rare earth is an important strategic resource in China,mainly distributed in the southern region of China.With the need of China’s economic development,a large amount of rare earth mining has caused serious damage to the ecological environment of rare earth mining areas,leading to frequent occurrence of geological disasters such as landslides,collapses,and debris flows,which has seriously affected the safety of the lives and properties of surrounding residents.Ecological slope protection technology is a slope protection technology that integrates relevant theories such as plants,soil,ecology,and mechanics.This technology has been applied in many practical river and highway slope projects,and has achieved effective results.According to the soil properties and climatic environment in the mining area,a new slope protection structure consisting of herbs,reinforcement materials,and ecological solidification agents was proposed.The ecological restoration test was conducted on the slope soil in the mining area,providing a reference for solving practical slope engineering problems.This paper takes the slope of the leaching site of the Datang tail ion type rare earth mine in Dingnan County,Ganzhou City,Jiangxi Province as the research object.In situ sampling was conducted in the mining area,and the physical and mechanical properties of the soil were tested through experiments.A mixed planting experiment of ryegrass and white clover was conducted using collected slope soil to test the shear strength,permeability,and ammonia nitrogen content of the root soil composite structure,and analyze the changes in plant growth status and soil strength after mixed planting.Using ryegrass stem as reinforcement material,shear strength tests were conducted on remolded soil samples with different reinforcement lengths and ratios to explore the reinforcement effect of ryegrass stem.Mix water-based polyurethane and bentonite as curing agents to explore the changes in soil strength after adding the mixed curing agent to the soil,and select the optimal mixing ratio from the test results.Combining herbs,reinforcement materials,and mixed curing agents,the stability and anti erosion ability of the slope protection system were verified through indoor simulated scouring tests.The main conclusions obtained through experimental research are as follows:(1)Through indoor tests,it was measured that the soil particle size of the mining area was less than 2mm,accounting for 91.18%.The soil particles below 2mm were screened and remolded.Triaxial tests were conducted on soil with different dry densities and water content.The test results show that with the same water content,the greater the dry density,the greater the soil cohesion and internal friction angle;With the same dry density,the soil cohesion and internal friction angle decrease as the water content increases.Different dry density and water content have a significant impact on the stability of soil.(2)Ryegrass and white clover were mixed and planted in different proportions for 77 days without artificial fertilization.Due to insufficient nutrients in the soil,the growth of ryegrass was affected,but white clover had the ability to fix nitrogen,providing the nutrients needed for the growth of ryegrass,enabling the growth of mixed plants to promote each other.The ammonia nitrogen content of mixed seeding soil was tested.The ammonia nitrogen content in the soil increased with the increase in the proportion of white clover,and decreased with the increase in the proportion of ryegrass.When the proportion of white clover accounted for more than 30% of ryegrass growth was normal,and when the proportion of white clover accounted for more than 40%,the ammonia nitrogen content in the soil was higher than the ammonia nitrogen content in plantless soil.Mixed planting can promote plants to adapt to harsher soil environments.(3)The soil cohesion of mixed plant root soil composite structure is related to the proportion of ryegrass and plant growth status.When the proportion of ryegrass and white clover is 50%,the shear strength reaches the maximum,and the cohesion is 343.4% of that of plain soil.When the proportion of white clover is 40% and the proportion of ryegrass is 60%,the permeability coefficient of the mixed plant root soil composite structure is the smallest,and the impermeability is the strongest.The root soil structure of plants can effectively improve the shear strength and impermeability of soil,and the stability of the root soil structure is related to the growth state of plants and the mixing ratio.(4)During the period of 10 to 30 days,the tensile resistance of ryegrass stem gradually increased,but the increase was relatively low.The increase in tensile resistance of ryegrass stem significantly increased during the period of 30 to 40 days.With the same stem length of ryegrass,the cohesive force of reinforced soil first increases and then decreases with the increase of reinforcement ratio,reaching a maximum value when the reinforcement ratio is 0.2%;The reinforcement rate of ryegrass stems is the same,and the cohesive force of reinforced soil first increases and then decreases with the increase of reinforcement length.When the reinforcement length is 20 mm,the cohesive force reaches the maximum value.Ryegrass stem is a good reinforcement material,and the best reinforcement effect is obtained when the reinforcement length is 20 mm and the reinforcement ratio is 0.2%.(5)Direct shear tests were conducted by mixing 19 groups of different mixing ratios of curing agent solutions with soil particles.When the specific gravity of bentonite in the curing agent solution is the same,the cohesive force of the soil sample first increases and then decreases with the increase of the specific gravity of waterborne polyurethane,reaching a maximum value when the specific gravity of waterborne polyurethane is 15;When the specific gravity of waterborne polyurethane in the curing agent solution is the same,the internal friction angle of the soil sample first increases and then decreases with the increase of the specific gravity of bentonite,reaching the maximum value when the specific gravity of bentonite is 12.The optimal ratio of sodium bicarbonate: waterborne polyurethane: bentonite:water=1:15:12:100 is the best,and the shear strength is the best.(6)Based on planting mixed herbaceous plants,multiple sets of slope erosion models were established,with a simulated rainfall flow of 100 L/h and a scouring time of 60 minutes.Compared to the scouring effect,the anti scouring ability of reinforced materials and mixed plants is insufficient.However,when mixed curing agents are added to the slope surface,the mucosa formed on the surface effectively resists the scouring caused by simulated heavy rainfall.The comprehensive test results show that the slope protection structure using mixed planting plants,reinforced materials,and curing agents as a system can significantly improve the shear strength of the slope soil and effectively improve the slope erosion resistance. |
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