Internal stresses in frozen ground: Reply

Abstract

the unfrozen soil. This pressure will be transferred immediately to the pore fluid of the unfrozen soil. With increasing frost penetration and concomitant ice lens formation, the heaving pressure (and hence, the pore-water pressure in the unfrozen soil) will steadily increase. Obviously, if the pressure transducers P, and P, measure total stresses, then at any time both pressures should be the same. This is not the case, as shown in Fig. 2a of the authors' note. Since the warm end is a draining boundary, consolidation in the unfrozen soil will occur as load is applied. In other words, as the applied stresses are transferred to the soil skeleton, the pore-water pressure will decrease. Since the pressures measured at P I (transducer located in the warmer region) declined slowly over several days, as reported by the authors, it appears that pore-water pressure was measured, not total pressure. For pressure transducer P2, located in the colder region, it appears that the pore-water pressure that was recorded as long as the soil was unfrozen has been locked in place by the frozen soil after the passage of the frost front. It would be of value to repeat the experiment with measurement of the overall heaving pressure using strain gauges or load cells and to compare the pressure measured at P2 with the actual heaving pressure. Finally, since the ice lens is an important aspect of this work, it would be valuable to know the location of the warmest ice lens in the authors' experiments. It would also be worthwhile to assess whether the soil around P I , which is at only -0. 10°C, is frozen, since it is known that as the pressure increases, ice may melt. If the soil is frozen at that location, and if the pressure in the system is 200 kPa as measured by P2, then according to thermodynamic relations for phase equilibria, the pore-water pressure should be about 80 kPa. The measured pressure in the unfrozen soil is only 25 kPa; this corresponds more closely to that expected according to consolidation theory, which predicts that the pore-water pressure should ultimately become atmospheric.