Dilatancy Characteristics of Soil

Abstract

The formulas of the relationship between stress ratios and strains due to dilatancy derived from the microscopic analysis based on observation of the particulate nature of soil (Matsuoka, 1973; Matsuoka, 1974) have been verified with respect to the measured data of drained triaxial compression and extension tests on sand and clay. From the test results, it is judged that dilatancy of soil may be governed uniquely by the shear-normal stress ratio ( τ / σ N ) on the mobilized planes or the principal stress ratios ( σ 1 / σ 3 , σ 1 / σ 2 , σ 2 / σ 3 ) as indicated by the above formulas. This concept differs from the view advocated by Shibata, Karube et al. (1963, 1964, 1965) that the volumetric strain caused by dilatancy is governed by the principal stress difference vs. mean effective principal stress ratio (( σ 1 − σ 3 / σ m ≡ q/p ). Further, it has been demonstrated that the stress-strain relationship in drained triaxial compression tests under a constant lateral pressure ( σ 3 ) and the stress path in undrained triaxial tests can be calculated by assuming the superposition of the above-mentioned strains due to dilatancy and the strains due to consolidation. Thus, it is inferred that dilatancy of soil as well as shear resistance (strength) may obey Coulomb’s law of friction.