Temperature dependencies of mechanical properties of soils subjected to freezing and thawing

Freezing temperatures are thought to be closely related to various types of frost damage, and therefore, the influences of differences in freezing temperatures on the physical and mechanical properties of soil subjected to freezing and thawing are studied. The samples used for the experiments are undisturbed volcanic ash cohesive soils of very high natural water contents (w = 85 – 110%) collected from below the frost depth at Tateshina Plateau, Nagano Prefecture, where various types of frost damage have occurred. Varying freezing temperatures at -1, -8, -18, and -25°C, samples are frozen in closed systems for 24 hr after which they are thawed for 24 hr in a constant-temperature, constant-humidity tank at +20°C and brought to a stationary condition, and then, various soil tests are performed and freezing temperature dependencies examined. From the results of consolidated undrained triaxial compression tests it is found that the cohesion of soil subjected to freezing the thawing is reduced and the ratio of the reduction is higher the lower the freezing temperature, while internal angle of friction is practically unaffected by freezing and thawing. Analogically inferred from the above, it may be considered that the mechanical properties of frozen soil are better the lower the freezing temperature, whereas the mechanical properties of frozen and thawed soil are more deteriorated the lower the freezing temperature. Therefore, in case of employing artificial freezing such as in the freezing method, it is necessary for designing and execution of work to be carried out paying thorough attention to the mechanical properties of soil after thawing.