Suffusion refers to the phenomenon that the movable fine particles in internally unstable soil migrate through the pore channels under seepage flow. The constitutive model

which describes the transition of the deposited fine particles to the fluidized fine particles in the pore fluid

determines the reliability of numerical analysis results. Currently

there are many constitutive models for suffusion based on constant hydraulic conditions

but the models considering the effect of hydraulic fluctuation are still lacking. First

the meso-mechanism of fine particle migration under different hydraulic conditions was summarized

and the particularity of the fine particle migration mechanism under fluctuating hydraulic conditions was highlighted. Then

based on the meso-mechanism

a constitutive model for suffusion was developed by using the volumetric exchange rate of deposited fine particles to fluidized fine particles. The model can consider the combined effect of the interstitial flow velocity

the variation rate of interstitial flow velocity

as well as the hydraulic action time. Based on a set of parameters

the model well reproduced the fine particle erosion process under various hydraulic loading paths in the existing experimental studies

demonstrating the effectiveness of the model.