THE STRENGTH OF REMOLDED SOILS AS AFFECTED BY EXCHANGEABLE CATIONS AND DISPERSIBLE CLAY

The tensile strengths of remoulded samples of five Australian soils wi th differing clay type, texture and shrink-swell potential were measur ed as a function of exchangeable cations (Na, Ca and Mg) and exchangea ble sodium percentage (ESP). Spontaneously and mechanically dispersibl e clays were also determined as a function of ESP. The tensile strengt h changed with the nature of the exchangeable cation, clay content and amounts of spontaneously and mechanically dispersible clay. In Ca-soi ls, the tensile strength was highly correlated with clay content and C EC. Regression analyses of data for soils containing various amounts o f exchangeable sodium showed that mechanically and spontaneously dispe rsible clay were individually correlated with the tensile strength of remoulded soils. However, multiple regression analyses of these data i ndicated that spontaneously dispersible clay alone was a major predict or of the tensile strength of remoulded sodic soils. This suggests tha t measurement of spontaneously dispersible clay adequately accounts fo r the differences in tensile strengths of dry remoulded soils as influ enced by ESP values. Analysis of variance of data for all the soils wi th varying ESP values showed that spontaneously dispersible clay was s trongly correlated with clay content. Analyses of data for individual soil type showed that spontaneously dispersible clay was highly correl ated with ESP. For each soil studied, increase in ESP resulted in incr ease of dispersible clay and hence in tensile strength. Although tensi le strength increased with ESP, the rate of change of strength with ES P was different for each soil. Soil with the highest clay content gave rise to the greatest rate of change. The effect of exchangeable magne sium on tensile strength was similar to calcium. However, in two of th e soils, exchangeable magnesium, in the presence of sodium, increased the strength slightly more than calcium, confirming the ionic radius e ffect of these elements.