Experimental system for one-dimensional freezing of undisturbed soil profiles

Abstract

An inexpensive and easy-to-handle setup for freeze-thaw experiments was developed. The system mimics field conditions, with a relatively deep monolith of undisturbed soil and a soil-air interface as an upper boundary condition. The setup includes a freezing device for vertical freezing of a soil monolith and transducers at several depths in the soil monolith for continuous measurement of unfrozen water content (TDR), temperature and radial temperature differences. The setup makes rudimentary control of boundary conditions and sophisticated monitoring of soil water and heat conditions possible. To study the performance of the system, soil temperatures and water contents in a clay soil monolith were measured during two freeze-thaw cycles. The setup was shown to be useful in terms of simulating freeze-thaw cycles in a lysimeter placed in the laboratory. One-dimensional heat flows could be simulated, with a thermal error (horizontal vs vertical heat flows) during freezing of about 5%. The setup was used to test the hypothesis that the similitude between freezing/thawing and drying/wetting holds for unsaturated clay soils. The results indicated a good agreement between water retention curves calculated from freezing-point depression data and from measurements, using pressure plates.