THE VARIATION OF CRITICAL-STATE PARAMETERS WITH WATER-CONTENT FOR 2 AGRICULTURAL SOILS

Triaxial tests were conducted on 436 reconstituted samples of two agricultural soils (a sandy loam and a loam) at moisture contents from air dryness to close to the respective liquid limits. Volume-change behaviour was largely consistent with the critical-state concept, the role of soil-moisture content being expressed in the values of the measured critical-state parameters. The most important parameters, and their inherent variability, have been specified. Most of the parameters varied systematically with soil-moisture content, but differently for the two soils. Some of the parameters were linearly correlated. The specific volume (v) was a linear function of the logarithm of the mean normal stress (ln p) during normal compression and along the critical-state line (CSL) with significantly different gradients (lambda and lambda*, respectively) at most moisture contents except close to the liquid limits. The standard errors of lambda* were typically of the same magnitude as the gradients found during hydrostatic unloading from two different v-levels whereas the standard errors of A were up to a factor of ten smaller. The linear projections of the CSLs on the deviatoric stress (q)-mean normal stress plane showed intercepts on the q-axis. Generally, precompaction leading to brittle failure had very little influence on the shear strength as compared with the strength in critical state.