A Review of the Thermodynamics of Frost Heave
KAREN S. HENRY
INTRODUCTION
um" also includes definitions of thermal, mechanical,
During frost heaving of soil when the soil is freez-
and chemical equilibrium, and the relationships among
ing from the top down, water in the soil pores flows
forces acting on systems in equilibrium are also exam-
upward to the freezing front because of a gradient in
ined. Significant contributions to the understanding of
the soil moisture pressure (or tension). This occurs even
frost heave, based on equilibrium thermodynamics, are
when the soil pores are not saturated. Ice lenses form
reviewed in "Thermodynamic treatment of frost heave."
and grow at or slightly above the freezing front and
This section begins with early work that led to the devel-
cause great uplifting forces. Understanding this pro-
opment of thermodynamic relations between water and
cess is not intuitive. However, thermodynamics, or the
ice in soil, followed by a brief presentation of the signif-
study of heat and work and the conversion of one of
icant aspects of two models of frost heaving. "Summary
these energy forms to the other, provides a means of
of current understanding of frost heave" summarizes
understanding frost heave. This report was written to
our current understanding of frost heave without the
make thermodynamic concepts accessible and to pro-
use of equations.
vide the background needed to help engineers and sci-
This report is an introduction to the thermodynam-
entists understand two aspects of soil freezing: the flow
ics of frost heave, and is not a comprehensive review
of water to the freezing front, and the initiation of ice
of all recent work on the subject or on frost heave mod-
lenses that cause the soil to heave. It is a review and
eling. Nonetheless, two areas of significant develop-
summary of 1) the thermodynamic principles that are
ment are mentioned below for those readers who want
important in modeling frost heave in soils, and 2) past
to pursue this topic in depth. This report will provide
research using equilibrium thermodynamics that has
some of the background required for further study of
contributed to the understanding of frost heaving. The
the material discussed below.
intent is for most readers to use this report without ref-
First, considerable progress has been made toward
erence to texts. For a more complete study of thermo-
understanding the nature of the unfrozen water that
dynamics, Castellan (1983) is highly recommended.
persists in soils at temperatures below the freezing tem-
Some difficult concepts are also illuminated very well
perature of bulk water (e.g., Dash et al. 1995, Wettlaufer
by Silver and Nydahl (1977).
1998). The focus of the work by Dash et al. (1995) and
The sections "Thermodynamic fundamentals" and
Wettlaufer (1998) is on isolating the roles that curva-
"Thermodynamic equilibrium" present material from
ture, confinement in pores, physical characteristics of
university senior-level physical chemistry, with a spe-
ice surfaces, and the presence of impurities in soil water
cial emphasis on topics relevant to freezing soils. Ther-
play on the thickness and mobility of unfrozen water in
modynamic definitions, concepts, and fundamental
freezing soils.
equations are provided in "Thermodynamic fundamen-
Second, regarding the ability to predict the defor-
tals." "Thermodynamic equilibrium" presents thermo-
mation of soils in response to freezing or thawing, engi-
dynamic equilibrium conditions and conditions under
neers have had great success in predicting material
which thermodynamic processes such as phase change
behavior by treating it as a continuum. Blanchard and
will spontaneously occur. "Thermodynamic equilibri-
Previous Page
