1287
Effect Evaluation of Freeze-Thaw on Deformation-Strength Properties of Granular
Base Course Material in Pavement
Évaluation des effets de gel-dégel sur les propriétés de résistance à la déformation des matériaux
granulaires de couche de base des chaussées
Ishikawa T., Zhang Y.
Hokkaido University, Sapporo, Japan
Kawabata S., Kameyama S.
Hokkaido Institute of Technology, Sapporo, Japan
Tokoro T.
Tomakomai National College of Technology, Tomakomai, Japan
Ono T.
Hokkai-Gakuen University, Sapporo, Japan
ABSTRACT: This paper examines the effects of freeze-thaw and water content on the deformation-strength properties of subbase
course materials to evaluate the mechanical behavior of granular base in cold regions. CBR tests of freeze-thawed subbase course
materials under various water contents, and the resilient modulus tests in unsaturated condition were conducted using two newly
developed test apparatuses. Moreover, these results were compared with long-term field measurement at a model pavement structure,
including FWD tests. As the results, it was revealed that the deformation-strength characteristics of unbound granular base course
materials deteriorate due to freeze-thaw and increment of the water content in thawing season. This indicates that the freeze-thaw of
granular base has a strong influence on the fatigue life of pavement structures.
RÉSUMÉ: Cet article examine les effets de gel-dégel et de la teneur en eau sur les propriétés de résistance à la déformation des
matériaux de couche de fondation de chaussée pour évaluer le comportement mécanique des bases granulaires dans les régions
froides. Des essais CBR de gel-dégel des matériaux de couche de fondation de chaussée avec diverses teneurs en eau, et des essais de
module résilient, dans des conditions non saturées, ont été réalisés à l'aide de deux appareils récemment mis au point. De plus, ces
résultats ont été comparés, avec les mesures de terrain à long terme, à un modèle de structure de chaussée, y compris des essais FWD.
Les résultats ont mis en évidence que les caractéristiques de résistance à la déformation, des matériaux granulaires de couche de base
non liés, se détérioraient en raison du gel-dégel et de l'accroissement de la teneur en eau durant la saison de dégel. Ceci indique que le
gel-dégel des bases granulaires a une forte influence sur la durée de vie en fatigue des structures des chaussées.
KEYWORDS: unbound granular base course matrials, freeze-thaw action, unsaturated soil, CBR test, triaxial test
1 INTRORDUCTION
In snowy cold regions such as Hokkaido, the 0 °C isotherm may
penetrate deep into pavement, thereby causing frost heave and
swelling of pavement surface, or cracking in asphalt-mixture
layer. Such phenomena specific to cold regions are thought to
accelerate deterioration of pavement structures and losing of the
functions. Recently, a theoretical design method that can predict
the long-term performance of transportation infrastructures has
come to be used as a structural design method of asphalt
pavement in cold regions. The theoretical design method can
take the above-mentioned degradation of pavement structures
into consideration. However, the frost-heave phenomenon and
the temporary degradation in the bearing capacity during the
thawing season have not been sufficiently elucidated as well as
the modelling of these phenomena. To develop an optimal
design method against fatigue failure of asphalt pavement in
Japan, it is necessary to understand the mechanical behaviour of
subgrade and base course during freeze-thaw in detail.
This paper examines the effects of freeze-thaw action and
water content on the deformation-strength characteristics of
subbase course materials to evaluate the change in mechanical
behaviour of granular base caused by freeze-thaw and
concurrent seasonal fluctuations in water content, and the
influences on fatigue life of pavement structures. For that reason,
we developed a freeze-thawing CBR test apparatus and a
medium-size triaxial apparatus for unsaturated soils. CBR tests
of freeze-thawed subbase course materials under various water
contents, and the suction-controlled resilient modulus (MR)
tests in unsaturated condition were carried out. Moreover, this
paper compares results of the above-mentioned laboratory
element tests with those of long-term field measurement at a
model pavement structure, including FWD tests.
2 TEST APPARATUS
2.1
Freeze-thawing CBR test apparatus
A schematic diagram of a freeze-thawing CBR (California
Bearing Ratio) test apparatus is shown in Figure 1. This test
apparatus is based on a general CBR test apparatus that has
been improved to reproduce the freeze-thaw history expected to
be applied to subbase course materials at the in-situ pavement
structures, in a laboratory environment. It has following
features:
–
The apparatus, which allows free water absorption or
drainage (open-system freezing) or suppresses it (closed-
system freezing) during the freeze-thaw process, can
perform a frost-heave test compliant with “Test Method for
Frost Heave Prediction of Soils (JGS 0172-2003)” on a
CBR test specimen (
=150mm,
H
=125mm).
–
Since the temperatures of both ends of the specimen are
controlled independently, the apparatus can subject a CBR
test specimen to a desired one-dimensional freeze-thaw
history at a constant freezing rate (moving speed of frost
line).
