Research And Application Of Soil Water Characteristic Curve Of Fine Grained Soil Based On Methylene Blue Value

The soil water characteristic curve is a curve of the key indicator that reflects the water holding capacity under the influence of external environment.It is of great significance to study the transfer of moisture and physical mechanical properties of unsaturated subgrade soil.Soil water characteristic curve can be used to determine the strength,permeability coefficient and volume strain of unsaturated soil.At present,the experimental measurement method of soil water characteristic data is often used to obtain the soil water characteristic curve,which is time-consuming and expensive.However,the indirect method of the mathematical model to get the soil water characteristic curve,is quicker and easier to get the results,and it makes a lot of researcher interests in this method.The characteristics of soil water holding capacity are related to the adsorption properties of soil.The higher the clay content is,the stronger the adsorption ability of soil will be to water.There must be a certain relationship between the soil water characteristic curve and the soil clay content.Based on the domestic and international methylene blue test methods,a colorimeter method of fine-grained soil was developed.And The methylene blue test of five kinds of soil samples was carried out,the methylene blue value which represents the clay content in soil was obtained.Then the soil water characteristic curves of the five soil samples were tested,and the parameters of the measured data were fitted with the Fredlund &Xing model,and the correlation between the parameters and the methylene blue value was analyzed.The prediction model of the parameters of Fredlund&Xing model was obtained.Through the methylene blue value and measured soil water characteristic curve of another soil sample,the reliability of soil water characteristic curve parameter model based on methylene blue value was verified.Therefore the characteristic curve of soil water can be estimated by methylene blue value.The results revealed the correlation rules of subgrade soil holding water ability and the methylene blue value.The results showed that the soil water characteristic curve would be more gently,and the value of the air entry value and the matrix suction of residual water content would be higher with a greater methylene blue value.According to the result of estimated soil water characteristic curve,the numerical calculation of subgrade humidity was carried out,and the change rule of subgrade humidity field was studied.The results showed that the moisture content of the subgrad will increase from the optimum moisture content during the construction period and would eventually reach a state of moisture balance.It will take a longer time for clay to reach the balance state than sand.The internal integral saturation of the clay roadbed is higher than that of the sand clay subgrade.In practical engineering,the methylene blue value is easy to be measured.According to the relationship between the methylene blue value and the parameters of the Fredlund&Xing model,the soil water characteristic curve of the subgrade soil can be obtained.And combined with the evolution of the subgrade humidity field,it can provide reference for the design of subgrade humidity.