Effects Of Biochar On The Deformation And Structural Strength Of Clayey Soils

In recent years,biochar has presented great potential in soil improvement,waste management and carbon storage.The application of biochar will have a significant impact on the physical,chemical and mechanical properties of the soil.In this study,the preparation and characterization of biochar were carried out with urban landscape defoliation and bagasse as raw materials.Based on the professionally prepared wood biochar,the effects of biochar on the volumetric deformation characteristics(expansion,shrinkage,dry shrinkage cracking)and mechanical properties(structural strength)of expansive soil and Xiashu soil were studied,combined with mercury intrusion test,scanning electron microscopy and matrix suction test,reveal the mechanism of action of biochar on expansive soil and Xiashu soil.Main conclusions are as follows:(1)Materials,pyrolysis temperature and other factors significantly affect the ash content,pH and pore structure of biochar,and the influence of pyrolysis duration on the properties of biochar is different.Bagasse biochar is more sensitive to temperature than leaf biochar.Under the same pyrolysis conditions,the pH and ash content of leaf biochar were higher than that of bagasse biochar,and the specific surface area and pore volume were much smaller than that of bagasse biochar.With the increase of pyrolysis temperature,the biochar ash content,pH,specific surface area and total pore volume of leaves and bagasse were significantly increased,and the micropore structure was more developed.As the pyrolysis time increases,the specific surface area and pore volume of biochar increase,and the microporous structure increases.However,when pyrolyzed at 600 ℃ for 4 h,the specific surface area and pore volume of the two biochars decreased,which may be caused by the pyrolysis of the biochar at a high temperature for a long time.In addition,the pH of biochar is positively correlated with ash content.(2)Biochar can reduce the compressibility of expansive soil and Xiashu soil,and the compression rate increases linearly with the increase of biochar content.Biochar can significantly change the structure of the soil and form an effective water migration channel in the soil to accelerate the compression process of the soil.Biochar has no obvious effect on the expansibility of expansive soil,but it can significantly increase the swelling of the loess.In addition,the particle size of biochar has no significant effect on the compressibility of expansive soil and Xiashu soil.(3)The effect of biochar on the evaporation and shrinkage characteristics of saturated mud samples is not only related to the amount of addition,but also affected by the evaporation stage.When the amount is more than 4%,the biochar can increase the evaporation rate of the expansive soil and the lower loess,and when the amount is less than 4%,the biochar inhibits the evaporation process of the soil.The main reason is that the higher amount of biochar changes the soil structure,and many channels are formed inside the soil,which facilitates the migration of moisture inside the soil to the surface layer and promotes the evaporation of the soil.Under low dosage conditions,it is difficult for biochar particles to form a connected water migration channel in the soil,so the effect on the evaporation process of the soil is not obvious,and even the evaporation rate decreases due to the pores between the bauxite particles.(4)In the process of evaporation and dehydration of biochar modified soil,the critical moisture content of initial fracture is not a fixed value,and the effect of biochar addition on critical moisture content is not obvious.When the amount of biochar is high,the evaporation rate of the sample is large,resulting in a shorter time for the sample to produce an initial crack.Biochar has a significant effect on the geometric characteristics of dry shrinkage cracking of clay.The fracture ratio,soil block and fractal dimension of the soil decrease with the increase of biochar content,and the number of fractures,total fracture length and number of nodes increase first and then increase with the increase of biochar content,which is related to biochar.Changed the mechanical strength and pore structure of the soil.(5)Biochar can increase the structural strength of the soil,and the structural strength increases more obviously with the increase of the dosage.Under high water conditions,the penetration resistance increases with the penetration depth,and finally tends to be gentle;when the water content is low,as the penetration depth increases,the penetration resistance first rises rapidly and reaches the peak,then starting to lower.