MEASURING NEGATIVE PORE WATER PRESSURES IN A FREEZING ENVIRONMENT

The measurement of negative pore water pressures is essential to the study of soil behavior in a freezing environment. Various devices are now available for suction measurements in unfrozen, unsaturated soils. The possibility of using these devices in the measurement of negative pore water pressures under freezing conditions is discussed. The thermal conductivity sensor appears to be a promising device for suction measurement. The thermal conductivity method of suction measurement in a freezing environment is examined. The theory of freezing soil and the thermal properties of soil are presented. Suction measurements in a freezing environment using thermal conductivity sensors from recent tests conducted at the University of Saskatchewan are also presented. The results are interpreted using the theory of freezing soil and the thermal properties of soil. The latent heat of fusion associated with the water phase transformation of water has significant influence on the thermal conductivity reading of the sensor during freezing and thawing. The formation of ice on freezing makes the interpretation of sensor reading difficult because of the significantly higher thermal conductivity of ice than that of water.