Effective stress paths and yielding in soft clays below embankments: Discussion

Konrad implies that this externally effective pressure, at the cold end, should result in the sample being pushed such that an equal pressure would be expected in the unfrozen soil at the warm end. This does not occur because the frozen part of the sample is firmly fixed to the sample holder. During the initial freezing, water is expelled at the warm end of the sample because of consolidation of the unfrozen, saturated soil. Once the frozen layer is fully formed we believe that the small pressure exerted by the warmest ice will essentially determine the total pressure for the unfrozen soil. The warmer transducer will show a small pressure whether it is just at the frost line or in unfrozen material. In our view, to understand the externally effective stresses and displacements of frozen ground it is not sufficient to consider the thermodynamic conditions at the frost line only. Rather, one must consider the thermodynamic phase-equilibrium relations throughout the soil, wherever the temperature lies within a few degrees below O"C. The mechanical (rheological) behaviour of the frozen soil must also be considered, because this defines the specific conditions within which the phase relations are applicable (Wood 1985).