Modeling the mechanics of freezing clay

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2005

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Title of Document: MODELING THE MECHANICS OF FREEZING CLAY

Sangjoon Han, Doctor of Philosophy, 2005

Directed By: Deborah J. Goodings, Professor Department of Civil Engineering

This research was initiated to investigate the freezing mechanisms of clay, and to make a contribution to the development of a simple analytical model that can characterize frost heave in clay. It was also undertaken to examine the correctness of modeling full scale frost heave in small models cooled on the geotechnical centrifuge to simulate full scale stress conditions. To this end, twenty-three physical model tests were conducted including 1g freezing tests, centrifuge freezing test. Two soils were used; three freezing regimes were applied.

Centrifugal acceleration was found to influence the magnitude, and the development of frost heave, as well as depth of freezing, and changes in local water contents after freezing, when compared to freezing of similarly sized models frozen at 1g. Ratios of (heave/depth of freezing) were similar in 1g and centrifuge models. No difference in the size of ice lenses could be observed. Evidence of freezing consolidation was observed.

Prefreezing water content strongly affected development of heave in terms of both magnitude of heave, and depth of freezing. Migration of water was modest at best; the position of the phreatic surface did not appear to affect the development and magnitude of heave. Local permeability, however, appeared to have an important effect on development of heave, linked to the rate of cooling.

An analytical model that was developed from this research explained, rather than predicted, frost heave at this point. The analytical model was satisfactory in characterizing magnitudes of heave, both ultimate heave and during development of heave, when the model included the assumption that heave can and does occur even when soil is not saturated, and the soil may transition from a prefreezing saturated condition to an unsaturated frozen condition.

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