Study On Engineering Characteristics Of Biochar-Amended Expansive Soiland Stability Of Shallow Surface Of Its Slope

Expansive soil is a special clayey soil that swells with water absorption and crumples with water loss,and this special characteristic leads to frequent geological problems of expansive soils.During the rainy season,expansive soil slopes are prone to damage of the shallow surface layer of the slope due to excessive changes in the water content of the shallow soil and serious erosion of the surface soil,which even further leads to phenomena such as landslides and slope instability,so the changes in the water content of the shallow soil and the erosion of the surface soil are the main factors affecting stability of slope.It has been shown that biochar can improve the water-holding capacity of soil and reduce the erosion of soil by rainwater,and it also has many green advantages.Therefore,this project is centered on the application of biochar in the protection of expansive soil slopes.Indoor tests,model box tests and numerical simulations are mainly used to study the effects of biochar mass ratios on the shear strength and permeability of the amended expansive soil and even the stability of the shallow surface layer of the slope,so as to provide theoretical guidance for future specific engineering practice.The main research contents and results are as follows:(1)The shear strength and saturation permeability coefficient(K_s)of the modified expansive soils with different biochar doping were measured,and the analysis of the relationship between shear strength and permeability coefficient and biochar doping was also supported by scanning electron microscope tests.The 5%biochar-amended soil had the lowestK_s and the highest shear strength among all the biochar modified soils.(1)By measuring the shear strength and saturation permeability coefficient(K_s)of the amended expansive soil with different biochar amendment content,the law of the effect of biochar amendment content on the shear strength and saturation permeability coefficient(K_s)of the amended expansive soil was investigated,and it was found that among all the doping levels of biochar-amended soil,the 5%biochar-amended soil had the lowest K_s and the highest shear strength.The mechanism of the effect of biochar doping on the shear strength and saturated permeability coefficient of the amended expansive soil was also explored and explained by scanning electron microscope tests.(3)Manila grass was planted on 5%biochar-amended soil slopes and expansive soil slopes,and the changes in soil temperature and volumetric water content were monitored for 60 days for both groups,and the growth of overlying plants was also observed.The test results showed that:the biochar-amended soil could reduce the temperature of the shallow slope and the variation of temperature,thus reducing the effect of atmospheric weathering on the shallow surface layer of the slope;under long-term natural conditions,the volumetric water content at the bottom of the slope of both expansive soil and amended soil was higher than that in the middle of the slope;the biochar-amended soil could promote the growth and development of plants and significantly reduce the variation of water content of the slope,and the variation of water content at the bottom of the slope of both groups was higher than that in the middle of the slope.The difference of water content variation between the two groups of slopes is greater than that in the middle of the slope,which is more conducive to maintaining the stability of the shallow surface layer of the slope.(4)Numerical simulations were conducted to study the safety factor of modified expansive soil slopes with different biochar admixtures content under rainfall conditions.The results show that:the addition of biochar can significantly improve the safety coefficient of Expansive soil slopes;the safety coefficients of slopes with 5%and 8%biochar amendment content under dry conditions are the highest,and the safety coefficient of slopes with 5%biochar doping decreases the least after the rainfall intensity increases.Therefore,5%is the optimal amount of biochar for improving the stability of expansive soil slopes under rainfall conditions and dry conditions.;increasing the thickness of modified soil layer can continuously improve the safety coefficient of slopes,but the improvement is not large.