Influence Of Root System On The Development And Evolution Of Cracks In Expansive Soil

It is of great significance to study the effect of root system on the development of cracks in expansive soil for understanding the mechanism of vegetation roots protecting expansive soil slope.In this paper,bermudagrass roots are mixed into expansive soil to make a ring cutter soil sample.The surface crack characteristics of the soil sample in the process of constant amplitude dry wet cycle are obtained,and the strength index of the soil sample at the end of the dry wet cycle is measured.The development law of the surface crack is evaluated from the surface crack characteristics,and the development degree of the internal crack in the soil is evaluated from the decrease of the strength index,and the soil compactness,temperature and root mixing rate are explored The influence of root diameter and root diameter on the crack development of expansive soil with roots.In addition,CT technology is used to obtain the internal crack development of the root bearing expansive soil column in the natural environment,and to explore the influence of the root system on the crack development of the expansive soil under the natural environment.The main research results are as follows:(1)During the dehumidification process,the moisture content gradient is the main reason for the crack development.The change trend of the surface crack rate and the average crack width of the soil presents a rapid growth stage and tends to be stable stage.The change mode of the surface crack rate is the average crack width;the number and connectivity of the cracks show an overall increasing trend;the average length of the cracks is sharp in the early stage of dehumidification In the later period,it decreased slowly and became stable.Vegetation protection of expansive soil slope should focus on the change of soil moisture gradient.(2)In the process of dry wet cycle,the development degree of surface cracks and internal cracks of root containing expansive soil with low compaction is higher;the development degree of surface cracks and internal cracks of root containing expansive soil under high temperature will rise to a certain extent.The density and temperature of soil should be paid more attention in the engineering of vegetation ecological protection expansive soil slope.(3)The root reinforcement can effectively restrain the development of surface cracks and internal cracks,and the effect of crack prevention is most obvious in the soil close to the natural slope density.The reinforcement effect of roots is more obvious in the expansive soil containing roots with high mixing rate and small root diameter.Developed root system,large number of root system and small root diameter are the important basis for selecting the dominant vegetation to protect expansive soil slope.(4)When roots are mixed into expansive soil,the inhomogeneity and dissimilarity of expansive soil containing roots are greatly improved.More cracks are developed near the contact surface of root and soil,which increases the number of surface cracks and reduces the average length and connectivity of cracks.(5)In the natural environment,the root system greatly reduces the crack rate and crack development depth of expansive soil at different depths.The root system has an obvious effect on cracking resistance of expansive soil.Vegetation protection is worth popularizing in expansive soil slope protection engineering.