Evolution of fissures and bivariate-bimodal soil-water characteristic curves of expansive soil under drying-wetting cycles

Periodical evaporation and rainfall cause the development of fractured soil, and the fracture has a strong influence on the hydraulic and strength characteristics of the soil.To study the crack development law and soil-water characteristics of expansive soil under the action of drying-wetting cycles, the CT scanning technique and image processing program are used to analyze the evolution process of fissures.The pressure plate instrument is used to test the soil-water characteristic curves of Hefei expansive soil and to study the effect of drying-wetting cycles.The results show that the CT scan combining with the image processing program can obtain the two-dimensional and three-dimensional structures of the internal crack of the sample and its quantitative analysis index, and the fracture development process of each fracture index can be described by the growth curve of the logistic function.The crack has a strong influence on the soil-water characteristic curve of expansive soil, and the one with cracks is in the form of "double peaks." With the increase of the number of drying-wetting cycles, the water-holding capacity of expansive soil is reduced, and the difference of soil-water characteristic curves of samples with different cycles is evident.At the high-suction stage, the soil-water characteristic curves of the expansive soil with different cycles gradually become consistent.The influence of drying-wetting cycles on the SWCC1 and SWCC2 feature points(intake value, residual value)is different.It is found that the average fracture width, internal surface area, average fracture length, fissure development degree of volume and fissure development degree of area are significantly correlated with the water-holding capacity of the expansive soil with cracks.The bivariate-bimodal soil-water characteristic curves are established with the number of drying-wetting cycles and the matrix suction as variables.The test data of soil-water characteristic curves of Hefei expansive soil is used to verify the accuracy and reliability of the model.The saturated water content and fitting parameters are well correlated with the number of drying-wetting cycles.