Experimentai Study And Model Amendment Of Soil-Water Characteristic Curve Of Unsaturated Aeolian Sand Subgrade Soil

Aeolian sand subgrade soil in the desert area of western Inner Mongolia is a typical unsaturated soil.Due to the effect of the special climatic conditions and temperature and humidity environment in the desert area,the soil-water characteristic curve of aeolian sand subgrade soil is significantly affected by factors such as moisture content,dry density,temperature,and salt content.In order to research the influence of various factors on the soil-water characteristic curve of aeolian sand subgrade soil and establish a corresponding revised model,this article used unsaturated aeolian sand subgrade soil in Alxa desert area of Inner Mongolia as an experimental soil sample.The matrix suction and total suction of soil samples under different conditions were tested by ASTM D5298-16 filter paper method.The influence laws of water content,dry density,temperature,salt content and different salts on the soil-water characteristic curve were analyzed.The significance of influencing factors was analyzed by orthogonal test design and grey correlation method.Based on theoretical derivation and data analysis,the temperature and salt content modified models of the van Genuchten model were established.The main conclusions of this article were obtained by studying :(1)Soil-water characteristic curve of aeolian sand subgrade soil is significantly affected by dry density and temperature.As the dry density increases,the soil-water characteristic curve tends to shift toward the upper right in parallel.That is to say,when the saturation is the same,the matrix suction and the water holding property increases with the increasing of dry density.And this effect is more pronounced in high suction areas with lower water content.As the temperature rises,the soil-water characteristic curve tends to shift to the lower right as a whole.That is to say,when the matrix suction in the soil sample is the same,its water content decreases with the increase of the equilibrium temperature.Moreover,the effect of temperature on the soil-water characteristic curve is more pronounced in high temperature or low suction regions.(2)Sodium sulfate content has an influence on aeolian sand matrix suction,osmotic suction and total suction.The matrix suction,osmotic suction,and total suction soil-water characteristic curves all shift to the right as the increase of the sodium sulfate content in the soil.When the volumetric water content is high,the salt content mainly affects the total suction by affecting the osmotic suction.However,when the volumetric water content is low,the salt content will have a certain effect on the matrix suction.The distribution forms of soil-water characteristic curve of sodium sulfate saline soil and sodium carbonate saline soil are basically similar.When the salt content is the same,the matric suction in the soil samples of sodium sulfate-salted soil is greater than that of sodium carbonate-salined soil at the same water content.(3)The results of SPSS range analysis,variance analysis,and grey correlation analysis show that the initial moisture content,the initial dry density,and the equilibrium temperature all have a significant effect on the matrix suction of aeolian sand subgrade soil.The order of significance is: initial moisture content> initial dry density> equilibrium temperature.(4)Based on the principle of thermodynamics,considering the influence of temperature on the surface tension and wetting coefficient,a v-G modified model of soil-water characteristic curve that can consider temperature effect is established.When fitting the soil-water characteristic curves of aeolian sand subgrade at different temperatures,the correlation coefficients of the model are greater than 0.93,and the fitting effect is good.By analyzing the relational expression between the v-G model parameters and the salt content and substituting into the v-G model,the v-G model parameters include the effects of salt content changes.The salt content modified models of matrix suction and total suction soil-water characteristic curve are suitable for fitting the matrix suction and total suction soil-water characteristic curves of Alashan sodium-containing aeolian sand respectively.