Swell properties of desiccated Regina clay
Abstract
Damage to structures founded on the lacustrine areas is common in western Canada. Adverse volume change exist in both fully saturated and partially saturated soils. However, their behaviour is still not completely understood. The purpose of this study is to investigate the volume change behaviour and swell potential of remolded and desiccated Regina clay.
Three series of Constant-Volume and Free-Swell consolidation tests were performed to observe the effects of back pressure on the compression and rebound curves and the difference in the rebound behaviour in the two types of tests. Also determined was the relationship between initial water content and swelling pressure, and degree of saturation and χ value. Pore pressure measurements were also made during the tests.
It is found that back pressure does not significantly alter the rebound slopes of remolded, desiccated samples for degrees of saturation in excess of 90 percent; however, there is an upward shift of the compression-rebound curves. The rate of volume change is found to decrease with applied back pressure and this is believed related to the presence of air in the sample.
The presence of air in the soil and measuring system decreases pore pressure responses considerably. The application of back pressure increases the accuracy in measuring pore pressures and gives an experimental settlement-log time curve which checks more closely with its theoretical curve.
The measured swelling pressures appear consistent with those measured by Noble on Regina clay. χ values, computed from the swelling pressure and soil suction, show a very rapid decrease with a decrease in degree of saturation.
Comparison of results from Free-Swell and Constant-Volume tests show a higher swelling pressure and rate of volume increase for the Free-Swell test. The slopes of the rebound curves are essentially the same for both types of tests.
For further confirming the effects of back pressure on volume change characteristics, future research should be carried out on samples with lower degrees of saturation. Samples prepared by static compaction would be satisfactory for such a study. It is also recommended that stress paths be taken into consideration in volume change investigations for partially saturated solls.