Measuring unfrozen pore water pressure at the ice-lens forming front

A method for measuring unfrozen-pore-water pressure at the ice-lens forming front in a frostheaving soil sample has been developed. The measurement results imply that the Generalized Clausius- Clapeyron equation (G.C.C.E.) might not be applicable to the precise simulation of the magnitude of frost heaving. Mechanical energy balance on a pore-water flow to an ice-lens yields an equation which shows that unfrozen-pore-water pressure at the ice-lens forming front is a function of the temperature, overburden pressure and water supply pressure. However, water supply pressure does not appear in the G.C.C.E.. Moreover the water intake amount given by the equation is half of that given by the G.C.C.E. The measurement method utilizes the characteristics of a super-heated state in which no segregation occurs and unfrozen water can flow. A test sample and a pressure sensor were both formed from Ohya-tuff, which is strong enough to easily realize a super-heated state. The unfrozen-pore-water pressure at the ice-lens forming front, the colder end of the sample, can be measured through the pressure sensor when the open, colder end of the sensor is set at the same level as the colder end of the sample. Measured results, namely the relationship between the change in the unfrozen-pore-water pressure and change in temperature, support the equation derived from the mechanical energy balance of a pore-water flow.