The influence of clay particles on the hydraulic conductivity of sandy soils

The relation between hydraulic conductivity and size of the sand particles and clay content was investigated in artificial mixtures of sand and clay and in natural soils, in four different ways in the laboratory and field.

In the artificial mixtures coarse aggregates of illitic clay hardly influenced conductivity. In fine sand, fine-clay aggregates caused a rectilinear decrease in conductivity with increasing clay content, but in coarse sand the curve was concave, because clay aggregates first block the bigger pores which in coarse sand were most important for water movement.

In subsoil of natural marine sands with little clay the same relation proved to exist between conductivity and the coarseness of the sand, as in clay-free sands but at a lower level. The influence of clay in reducing conductivity was similar in all coarse and fine sands. Small amounts of clay reduced conductivity considerably more than larger amounts, which agreed with the effect of adding fine clay aggregates to coarse artificial mixtures.

Field results from three methods yielded a table giving the relation.