Exchangeable sodium, subplasticity and hydraulic conductivity of some Australian soils

The hydraulic conductivities of beds of packed fragmented material from a variety of clay soils (mostly normal plastic but including some subplastics) and some non-clay soils, have been measured using high quality water. The degree of swelling of each packed bed (originally air-dry) was also determined. The data have been examined in relation to the exchangeable sodium percentage (ESP), clay content and type, and the degree of subplasticity. For the normal plastic soils, ESP influenced the hydraulic conductivity more than any other property. Its influence was independent of clay content and type. The results support the premise that an ESP much less than 15 should be accepted as the value above which soils can be adversely affected physically; a value of 5 would be more relevant. For the subplastic soils, the hydraulic conductivity was independent of ESP, and swelling was small considering their clay contents.