Drainage Layer Fouling as a Consideration in Capillary Barrier Design

The combined effects of various levels of hydraulic flow regimes and applied loads on the stability of the interface between the coarse and fine layers of a capillary barrier cover system were investigated by performing series of laboratory experiments in specially designed flow columns. The fine layer (silt loam soil) was placed at dry densities of 1.54 and $1.70\mathrm{g}∕{\mathrm{cm}}^3$ corresponding to 89 and 98% of the maximum dry density, respectively, over a coarse layer (gravel, at a dry density of $1.55\mathrm{g}∕{\mathrm{cm}}^3$ ). Water was introduced at flow rates ranging from 420 to $8,600\mathrm{mL}∕\text{day}$ corresponding to flux rates ranging from 1.57 to $55.5\mathrm{cm}∕\text{day}$ . The colloids mobilized from the silt loam soil (fine layer) used for this study did not significantly affect the stability of the interface and the structure of the fine layer. Thus, the fine layer material is self-filtering. The critical fluxes required to cause significant migration of particles from silt loam placed at 1.54 and $1.70\mathrm{g}∕{\mathrm{cm}}^3$ are 10 and $35\mathrm{cm}∕\text{day}$ , respectively. The upward intrusion of gravel materials into the overlying fine is dependent only on the placement/compaction density of the silt loam soil.