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Study on the pore flow distribution within binary granular packings during suffusion

Internal erosion; Suffusion; Pore flow distribution

Suffusion involves the migration of finer particles within the voids of coarse skeletons in soils
under seepage flow. It is often encountered in binary granular packings featured by relatively wide
PSDs without sufficient medium-sized particles, e.g., gap-graded soils featured by a hiatus of
particle sizes. Suffusion has gained special attention in previous research due to its significant
threats to the safety of earth structures, e.g., dam foundations, colluvial slopes and soil-rock
mixture embankments. The coupling between the finer particle loss and the evolution of pore fluid
flow is a key mechanism for the development of suffusion. In particular, the nonuniform
distribution of pore fluid flow within the binary granular packing should play a critical role in the
coupling procedure, however, a quantitative evaluation on it is still needed. To this end, this study
investigated the flow velocity distribution within the coarse skeleton pores of binary granular
packings with various finer fractions during suffusion. A coupled Computational Fluid Dynamics
(CFD) - Discrete Element Modelling (DEM) approach that combines the resolved and un-resolved
coupling schemes was used to obtain the pore flow velocity. The probability density distribution
of pore flow velocity within the coarser skeleton presents an exponential decay at various finer
fractions before suffusion. With the loss of finer particles, the probability density distribution still
follows an exponential form although the distribution may tend to be more uniform or non-uniform
depending on the percentage of finer particle loss.