Experimental Study on the Elastic Modulus of Unsaturated Expansive Soil Using the PIV Method

The stiffness and deformation of expansive soil is closely related to its water content state. To reveal the correlation between the elastic modulus and water content of unsaturated expansive soil, this study proposes a method for calculating and analyzing elasticity models based on particle image velocimetry (PIV). Typical expansive soil from Nanning, Guangxi was taken as the research object. Remolded ring-knife specimens with different dry densities were prepared. The particle image velocimetry (PIV) method was used to continuously collect high-definition image sequences and mass change data of the samples during the process from saturation to drying. Combined with the measured results of the soil-water characteristic curve and Poisson’s ratio, the elastic modulus of the soil samples at different water content states during the dehumidification process was calculated based on the suction stress theory and the generalized Hooke’s law in polar coordinates. The test results show that the elastic modulus of unsaturated expansive soil increases exponentially with the decrease of saturation, and the initial dry density of the soil samples has a significant influence on the stress-strain process. Based on the experimental data and the Levenberg-Marquardt algorithm, the mathematical model E = a-bc^w for the relationship between the elastic modulus and water content of unsaturated expansive soil was fitted, which can accurately describe their nonlinear correlation.