Testing and constitutive modeling of cemented soils.

The behavior of cemented sands is examined experimentally and theoretically in this study. The first segment of the investigation involves an extensive laboratory program to examine the effects of slenderness ratio, effects of cementation, and effects of confining pressure on the stress-strain curves of cemented sands. Results show that specimens with slenderness ratio of 1.5 or greater exhibit lower strength, higher dilatation rates, and relatively brittle behavior when compared to samples with slenderness ratio of 1. Furthermore, cemented sands have an essentially straight line Mohr-Coulomb failure envelope, whose cohesion intercept increases with the degree of cementation of the soil. The effective friction angles measured for cemented sands with various cementation levels are in the same ranges as the effective friction angle evaluated for uncemented sands. Moreover, failure modes of the material varies from brittle to ductile depending upon the level of cementation and the degree of confinement. In general, as cementation increases, cemented sand exhibits a brittle failure behavior; while increasing the confining pressure causes a ductile failure response. The second portion of the project includes development of a constitutive model for cemented sands. Cemented sand is viewed as a multi-phase material comprising three phases: sand, cement, and pore water. The elastoplastic behavior of cemented sands is the consequence of the behavior of the individual phases plus the interaction of the phases. The individual phases (sand and cement) are modeled using the theory of plasticity. Mixtures theory is used to assemble the individual phases to simulate the overall behavior of cemented sands. The gradual damage of the internal structure of cemented sands is also incorporated within the model. The agreement between experimental data and model predictions is very good. In summary, mixtures theory using simple plasticity models for the individual phases is capable of capturing the complex behavior of cemented sands