Experimental Study On Water Retention And Permeability Characteristics Of Expansive Soil With Roots

With the increasing awareness of ecological protection,ecological protection has become a popular choice for expansive soil slope protection.In this paper,the expansive soil of Nanning Buffalo Research Institute in Guangxi is taken as the research object.Based on the unsaturated soil mechanics theory,the influence law of water holding and permeability of pure expansive soil and root containing expansive soil is studied by indoor and field experiments.The effect and mechanism of root soil composite on Soil permeability is analyzed,and the influence of vegetation root on the permeability of expansive soil is explored Sound effect.The main research results are as follows:(1)Both the degree of compaction and the ratio of mixing roots have an impact on the water-holding performance of expansive soil.The higher the degree of compaction,the greater the intake value of soil samples,the better the water-holding performance.This phenomenon is especially obvious in the low suction range.The effect of root incorporation rate is reflected in the lower water holding capacity of soil samples with higher root content.(2)The saturated permeability coefficient of pure expansive soil is very small at high pressure compactness.With the decrease of compactness,the saturated permeability coefficient of expansive soil will increase correspondingly.The soil sample with a compaction degree of 75% increases by about two orders of magnitude compared with that with a compaction degree of 95%.The permeability coefficient of soil samples with different root mixing ratios is greater than that of pure expansive soil,and the saturated permeability coefficient of soil increases with the increase of root mixing ratio.(3)There is a nonlinear relationship between unsaturated permeability coefficient and matric suction,and the larger the matric suction in expansive soil,the smaller the corresponding permeability coefficient will be.The degree of compaction and the ratio of root mixing have an influence on the permeability coefficient to a certain extent.The lower the degree of compaction of expansive soil or the higher the ratio of root mixing,the smaller the permeability coefficient will be.(4)The initial permeability coefficient of the field grass-planting slope is slightly larger than that of the bare slope.The permeability coefficient of the grass-planting slope reaches a stable state earlier than that of the bare soil slope,and the permeability coefficient of the final stability is about an order of magnitude higher than that of the bare soil slope,indicating that the presence of vegetation roots can significantly improve the permeability of expansive soil.(5)The dry-wet cycle will accelerate the development of cracks in expansive soil,and the existence of cracks will provide a new channel for water flow infiltration.Therefore,there is a significant corresponding relationship between the saturation permeability coefficient of expansive soil and the surface fracture rate.The higher the surface fracture rate is,the greater the saturated permeability coefficient will be.The soil permeability coefficient can reflect the development of soil fractures.The root soil complex formed by the combination of root and expansive soil can prevent the development of fissures to some extent,thus reducing the infiltration of water flow.