A study of critical state on an unsaturated silty soil

Abstract

Critical state models for unsaturated soils have been proposed in recent years; however, the proposed models have been based on limited experimental data. Compacted specimens have generally been used for research, and the complications of soil fabric resulting from the compaction procedures have brought difficulties into the interpretation of fundamental soil behavior. There is a need to undertake further laboratory research studies on unsaturated soils, particularly to obtain a fundamental understanding of the shear strength and critical state of unsaturated soils by testing soil specimens with simple soil structures. Suction-controlled triaxial drained shear tests on an unsaturated silt were carried out as part of this research program. Specimens were prepared by gradually consolidating the initially slurried soil. The resulting specimens had a relatively simple soil fabric and stress history. The results showed that applying suction to an initially saturated specimen has a similar influence on the stress–strain behavior and critical state characteristics as does increasing its density by applying a higher confining pressure. The critical state lines for the unsaturated soil corresponding to different soil suctions are parallel to those for the saturated soil on the (q : p' ' ), (v : p' ' ), and (vw : p' ' ) planes.Key words: critical state, shear strength, unsaturated soils, volume change, triaxial testing.