A laboratory study on dredged lumpy clay subjected to a freezing-thawing cycle

Abstract

This paper discusses pore pressure response of clay-lumps and slurry mix when subjected to freezing and thawing cycle. This study was undertaken to access the adequacy of the thawed sample in flexible wall permeameter tests. Speswhite kaolin clay was used in all the tests. A 100 mm diameter cylindrical block of known volume of clay lumps and clay slurry was prepared in a split mould. The sample was then allowed to gradually freeze in a chamber maintained at -10 and -18 0C. The sample was then allowed to thaw in two different test conditions. In the first case, the samples were allowed to contract and volume permitted during de-freezing. In the second case, volume of the sample was maintained constant during de-freezing. In all the cases, the tests were conducted using a flexible wall permeameter. The permeameter was modified to take independent measurements of pore pressures within the lumps and within the slurry using miniature pore pressure transducers (PPTs). The effect of temperature and confining pressure on the pore pressure was observed. It was observed that freezing caused transient increase in the pore pressure. The pore pressure increase was noticeably higher in the clay slurry than in the clay lumps. Beyond the transient peak, the pore pressures reduced to negative because the ice lens generated suction in slurry and lumps. The magnitude of pore pressure decrease was more in the lumps than the clay slurry. It was also observed that the samples which were frozen at a faster rate, exhibited less loss in water content wen thawed compared to the samples which were frozen at a slower rate. This will have significant effect on the shear strength and softening of permafrost soils which are now thawed because of climate change.