THERMODYNAMIC TREATMENT
OF FROST HEAVE
Ice
Early contributions
The first researchers to make significant progress in
understanding frost heave were Taber (1929, 1930) and
Beskow (1935). Taber (1929, 1930) established with
certainty that frost heave does not occur because of the
expansion of soil water upon freezing. He proved that
c:a 0.001 mm
pore size influenced the total amount of frost heave for
given freezing conditions and that saturated material
with very small pores retains unfrozen water at several
degrees below freezing. Taber (1929) established that
the pressure from frost heaving is due to the direction
c:a 0.02 mm
of ice crystal growth, which is, in turn, controlled by
the direction of heat loss. He deduced that slow crystal
growth favored frost heave, and introduced the idea that
water exists in a state of tension.
Taber (1930) treated freezing soils as open systems.
He developed the idea of a gradient in soil moisture
Figure 3. Frost line in two soil types. The upper part
of the figure represents a fine-grained frost-heaving
tension that causes water above the water table to flow
soil and the lower part of the figure is a coarse-grained
to the freezing front. He also observed that the rate of
frost-heaving soil (e.g., a coarse silt). The scale of the
heave is continuous under constant temperatures applied
upper diagram is about 20 times that of the lower dia-
at the top and bottom of soil specimens even though
gram. The arrows show the maximum distance that
the ice lenses are separate and distinct from each other.
water must travel for frost heave to occur. (After Bes-
kow 1935.)
Taber hypothesized that during the growth of an ice
layer, voids underneath it gradually fill with ice, begin-
drying, and 2) that in reference to soil water and soil
ning with the larger ones. As the resistance to the flow
pressures, Beskow usually (but not always) expressed
of water to the ice lens increases (because of the pores
them in terms of head.
filling with ice), a new layer of ice begins to form near
One of the most important ideas contributed by Bes-
the bottom of the zone of the frost penetration. This is
kow (1935) is that soil freezing is similar to soil drying--
the beginning of the idea of a "frozen fringe," a zone at
in both cases water changes phase and the amount of liq-
the freezing front where ice has penetrated the pores,
uid water in the soil decreases. Thus, water flow from
contains no ice lenses, and has very low hydraulic con-
above the water table to the zone where water is chang-
ductivity that can limit rate of heave.
ing into ice is analogous to flow of water to a zone
Working independently from Taber, Beskow (1935)
where it is evaporating.
also contributed several important concepts to the under-
In describing soil freezing, Beskow (1935) noted the
standing of soil freezing. However, the English transla-
freezing point depression of soil water due both to sol-
tion of Beskow's 1935 report on frost heave is long,
utes in the water and the "effect of the particle system"
difficult to follow, and uses terms that are not well
(adsorbed water). He constructed freezing temperature
defined. Some clarifications of terms that he used are
curves, showing unfrozen water content vs. tempera-
listed here.* In Beskow's report, soil water is referred
ture and noted that, for saturated fine-grained soils, even
to as capillary water, and adsorbed water is called the
the water in the center of the pores is considerably influ-
water under the radius of influence of the particle. The
enced by the particle surface. Ice crystallization is
term "capillary pressure" or "positive capillary pres-
favored farther away from a particle surface and the
sure" means soil moisture tension. Effective stress (a
surface of the ice protrudes down into the pores, with
concept that was not yet well-developed) was referred
adsorbed water adjacent to it (Fig. 3). Beskow explained
to as "total compressive force," or just "pressure." Two
that when an adsorbed water film becomes thinner, an
other things are noted: 1) that Beskow described only
increased negative pressure occurs in the unfrozen soil
the "saturated capillary fringe" in all of his discussions
water that induces water to replenish the film.
that refer to the similarities between soil freezing and
Beskow (1935) documented the influence of effec-
tive stress on frost heave. He said that the total com-
* These terms and their definitions refer only to Beskow's report;
pressive force acting on soil particles during freezing
they are not necessarily terminology used today. They are pro-
was the sum of the actual load (overburden) pressure
vided for the convenience of those who will read his work.
8
Previous Page
