Constrictions and filtration of fine particles in numerical granular filters: Influence of the fabric within the material

摘要

Granular filters in earth dams or retaining structures are supposed to control the migration of finernparticles flowing under seepage through the structure. The role they play is critical since some old dams whichrnhave been constructed without filters have suffered from large disorders if not failure from this erosion. Indeed,rnthe transport of fine particles let large voids within the structure and, at a final stage, can induce the creation ofrna breach through the structure. Past studies have shown that constrictions which are the narrowest paths betweenrnpores in the granular filter are the key entities able to explain the filtration properties of the material. Indeed, if arnfine particle finds on its path a constriction of size smaller than its own size, the particle will be stopped by thernfilter. The possibility of finding such constriction size is given by the cumulative Constriction Size Distributionrn(CSD). Like a Particle Size Distribution, a CSD does not hold a directional property meanwhile the pathwayrnwhich is mainly ruled by the gradient of hydraulic head is directional.rnA DEM study of a granular filter composed of spheres has been performed in order to understand howrnthe fabric within the sample modifies the orientation of the constrictions and how the filtration properties arerninfluenced by the direction of seepage with respect to the fabric within the sample. It seems that there is anrnimpact of the fabric on the filter properties which incites us to question the way CSDs are used in the design ofrnfilter criteria.