Model for Piping‐Plugging in Earthen Structures

A capillary model was developed to predict under what conditions piping versus plugging is likely to occur as a result of clay particle dispersion in soils. In the intermediate size range, i.e., particles too small per se to clog pore constrictions and too large to wash through unimpeded, the outcome depends strongly on the concentration of dispersed particles in the seepage stream. This concentration in turn depends upon the rate at which the particles are eroded from the pore walls. The capillary model was used to ascertain the relationship between key variables at the onset of piping. This relationship involved the initial permeability and porosity of the soil, the critical tractive stress, and the hydraulic gradient. The model was also used to predict under what circumstances clay particle concentrations in a seepage stream will buildup suddenly to very high values, a condition favorable to clogging or particle holdup. Results of the analysis showed that very large particle concentration buildups tend to occur at permeabilities of less than ${10}^{-9}{\mathrm{cm}}^2$ ${10}^{-4}\mathrm{cm}/s$ for water at $20°C)\text{.}$ This prediction is consistent with previous findings reported in the geotechnical literature.