Abstract: Suffusion, a phenomenon involving the migration and loss of movable fine particles through pore channels in internally unstable sandy soil, is one of the primary triggers of seepage failure in poorly-graded geological bodies or geotechnical structures such as dams. However, existing models of suffusion rate often suffer from limitations such as strong empirical dependence, poor parameter measurability, and unclear physical significance. To address these issues, this study explains why the total amount of erodible fine particles in sandy soil remains finite, from the perspectives of suffusion meso-mechanisms and energy dissipation. Suffusion is defined as an energy dissipation process induced by the mechanical work performed by fine particles within the soil matrix. Subsequently, through analysis of the intrinsic mechanisms and energy conversion during suffusion, a suffusion rate model for sandy soil under constant hydraulic gradient is proposed. The model introduces the maximum cumulative loss ratio and the erosion coefficient as key parameters. These parameters are expressed as functions of critical factors such as experimental conditions and soil characteristics, which are determined and calibrated based on the energy dissipation principle and dimensional analysis, respectively. Finally, the model’s validity is verified using experimental datasets from published literature. The results demonstrate that the proposed suffusion rate model for sandy soil effectively captures both the finite total loss of fine particles and the decay characteristics of the suffusion rate. Utilizing a single set of parameters, the model successfully describes the fine particle loss process for the same soil type under different constant hydraulic gradients. The development of this model enhances the understanding of the intrinsic mechanisms governing suffusion in sandy soil and establishes a theoretical basis for the quantitative analysis of suffusion processes.

Key words: suffusion of sandy soil, mechanical work, energy dissipation, suffusion rate model, dimensional analysis