An experimental study of uniaxial compressive strength of segregated ice in soil

Abstract

Uniaxial compression tests of columnar-grained ice which was segregated in soil specimens were conducted. Specimens (5 cm in diameter and 9 cm in height) were prepared by using frost susceptible clay which was sampled from Tokyo. The tests were carried out systematically with respect to the dependence of compressive strength on temperature, direction of loading, strain rate and specimen height.When the load is applied ta the direction of ice growth, the longitudinal uniaxial compressive strength increases with the lowering of temperature, giving values of 190 kgf/cm2 at -10°C and 250 kgf/cm2 at -20°C. These values are larger than those of various types of ice, Fujinomori frozen clay and Toyoura frozen sand. When the loading is perpeiadicular to the growth directian, the lateral uniaxial compressive strength is approximately equal to the commercial ice strength, being about 50 kgf/cm2 at -20°C. The compressive strength, when the loading is applied to the ice growth direction, has a maximum at a strain rate of between 0.5%/min and 2%/min for -3°C. When the initial specimen temperature was about -0.4°C. the specimen temperature dropped with partial fusion during compression at a faster strain rate than 0.4%/min, and consequently the relation between the longitudinal strength and the specimen temperature agrees with the relation between pressure and freezing point calculated from the Clausius-Clapeyron equation. For a constant strain rate, the longitudinal strength decreases as the specimen height decreases from 15 cm to 1 cm For a height less than 1 cm, on the other hand, it decreases. When the load is applied to the direction of ice growth, the transition from ductile failure to brittle failure occurred at the strain rates of 0.6, 0.2 and 0.04%/min for constant temperatures of -1.7, -3 and -18°C, respectively. In the range of ductile failure, grain boundary cracks and grain inside cracks are distributed regularly in the growth direction and/or perpendicular to it.