Abstract: Indoor measurements of the soil-water characteristic curve (SWCC) often require a long equilibrium time, yet the actual soil changes may not meet this requirement. When the time scale is small, the SWCC may not reach equilibrium. If the equation for unsaturated soil is still established using the soil-water characteristic curve under equilibrium conditions, errors may occur. Therefore, the dynamic effect of the soil-water characteristic curve under non-equilibrium conditions was studied. Based on existing theories, we derived the relationship between the parameters of the soil-water characteristic curve and the rate of saturation change, and subsequently established a dynamic capillary hysteresis model using the derived dynamic parameters. We developed a self-designed SWCC rapid measurement device and conducted soil-water characteristic curve measurements for coarse sand and fine sand under varying rates of saturation change. The experimental research revealed that: 1) the parameters of the soil-water characteristic curve exhibit significant dynamic effects; 2) the air entry value and residual saturation are not constant, but vary depending on the rate of saturation change; and 3) the model was validated using the experimental results, and the prediction outcomes of the dynamic model closely matched the experimental results, demonstrating the model's rationality. This study provides a more practical theoretical basis for solving problems related to deformation, strength, and seepage in unsaturated soils.

Key words: soil-water characteristic curve, suction increment, hydraulic parameters, dynamic effects, hysteresis model