Experiments on heaving pressure were conducted with a saturated clay under partially freezing in a closed system.
Measurement of drop in prestressed pore wate pressure P_w was continued under constant total pressure P until change of P_w ceased, maintaining the constant temperature at both ends of specimen above and below freezing respectively. The elapsed change of pore water pressure continued for a long time and it was observed that ice lens was growing in the vicinity of cooling surface. These facts reveal that the veins of unfrozen water are connected from freezing front, where only free water freezes, to ice lensing interface and unfrozen water migrates slowly in frozen soil. When the partially frozen soil can draw water no more under the effective stress calculated from P and P_w, we define this effective stress as upper limit of heaving pressure σ_u. σ_u obtained depends clealy upon the temperature at cooling surface θ_c and empirical formula is obtained as follows,
σ_u= -11.1θ_c [kg/cm²]
This formula agrees with modified Clausius-Clapeyron equation that gives the change in freezing point in the case where the pressure on the ice differs from that on the water. This agrees with the experimental results obtained by Radd and Oertle (1973) but differs from maximum heaving pressure calculated from “Capillary Force Theory” in which it is constant, not depending on temperature.