Formation of ice layer continuously segregated in soil freezing

Abstract

The segregation of ice at the freezing front of soil constitutes the most characteristic feature of frost heave phenomena. To quantitatively determine a condition in which the state of ice segregation is brought about, continuous segregation of pure ice was reproduced in a laboratory experiment conducted in an open system using a newly designed apparatus. Used as a specimen was a markedly frost-susceptible Kanto loam, in the shape of a cylindrical column, under water-saturated conditions free from load. This apparatus is capable of adjusting heat flux in the vicinity of the freezing front by controlling temperature at the upper (cold) and the lower (warm) cylindrical surfaces of the column. The apparatus provides a steady-state method of keeping a heave rate constant under the condition in which the temperature gradient is kept constant in the vicinity of the freezing front by suspending the movement of the freezing front, irrespective of the heave amount and heave rate.
The following conclusions were drawn from the experiment : to keep a specific temperature gradient across the frozen soil constant during ice segregation, the heave rate changes from a maximum value to zero as the temperature gradient across the unfrozen soil increases in steps. The maximum value called the critical heave rate, determines the range of formation of ice segregated and depends upon the temperature gradient across the frozen soil. The critical heave rate is in proportion to the temperature gradient across the frozen soil. Then, the constant of proportionality is 2.66× 10^-5 cm²/s°C, which characterizes the frost-susceptibility of a given soil.