Study On The Effects Of Hydration On Expansion And Shrinkage Characteristics Of Collapsed Soil

Rainfall is the main driving force on the development of collapsed soil,and the change of the water content in the soil is the main factor that cause collapsing.In order to investigate the reason and the mechanism of collapse erosion,the different layers in the collapsing soil were taken as the research object in this thesis.The expansion and shrinkage characteristics of different layers in the collapsing soil,which under different initial conditions were studied.Then the feasibility,which utilizing the surface charge density and zeta potential to calculate the thickness of the sliding layer and diffusion electric double layer of soil colloidal particles,extracting from different layers of collapsing soil,was explored from the perspective of diffusion electric double layer theory and hydration reaction,In the meanwhile,the effects of the thickness of the sliding layer on the expansion and contraction characteristics of the collapsed soil were discussed.The main conclusions are as followed:(1)The liquid-plastic limitation reduce with the increase of soil depth.The liquid-plastic limit of the red soil layer is the largest,the sand layer is the smallest,and the detritus layer is the middle,wherein the red soil layer is a high liquid limit clay.The swelling potential of the red soil layer in the collapsed soil is greater than that of the sand layer and the debris layer.The kaolinite is the main clay minerals in the collapsing soil,and do not contain strongly hydrophilic clay mineral such as montmorillonite.The content of Illite is around 10%.(2)After regression analysis of initial water content and no-load expansion rate,initial water content and linear shrinkage rate,we found that: A significant exponential decreasing relationship between the initial water content and the non-charge expansion rate of different soil layers was found.The fitting regression equation obtained by different soil layers can be expressed as: δe=ae(-ω/b)+c.An inverse exponential increasing relationship between the initial water content and the linear shrinkage of different soil layers in the collapsed hill was also found.The fitting regression equation obtained by different soil layers can be expressed as: δsl=ae(ω/b)+c.(3)The maximum unloading expansion rate and maximum linear shrinkage rate of the different soil layers is largest in the red soil layer,the sand layer is middle and the debris layer is small.It indicated that the expansion and shrinkage performance of the collapsed soil gradually decreases with the increase of the soil depth.This irreversible expansion and shrinkage phenomenon may be the cause of cracks in the collapsed soil.(4)As the electrolyte concentration increases,the thickness of the electric double layer of the colloidal particles is compressed,and the thickness of the sliding layer becomes thinner,causing particle agglomeration.The macroscopic performance of particle agglomeration is soil shrinkage.As the electrolyte concentration decreases,the thickness of the sliding layer of the colloidal particles becomes thicker,the particle spacing increases,and the particles are easily dispersed.The diffusion caused by the increase in the particle spacing is macroscopically expressed as soil swelling.The ingress or loss of water will has an effect on the concentration of electrolyte in the soil,and the change in electrolyte concentration will cause a change in the thickness of the sliding layer,which will affect the expansion and contraction of the soil.Therefore,combined the expansion and contraction characteristics of the collapsed soil with the theory of the diffusion electric double layer,it can be inferred that the thickness of the sliding layer of the colloidal particles in the collapsing soil affects the soil expansion and contraction.