3411
One-dimensional compressive behaviour of reconstituted clays under high
temperature and small strain rate
Comportement oedométrique des argiles reconstituées sous fortes température et à faible vitesse
de déformation
Tsutsumi A.
Foundations Group, Geotechnical Engineering Field, Port and Airport Research Institute, Japan
Tanaka H.
Division of Field Engineering for the Environment, Graduate School of Engineering, Hokkaido University, Japan
ABSTRACT: It is considered that a long term settlement of clay deposits so called secondary consolidation is caused by clay
viscosity. In this paper, the viscous property of clayey soils is examined from two viewpoints of temperature and strain rate effects.
To investigate these effects, constant rate of strain (CRS) loading test, in which the strain rate is changed during the test, was carried
out at a temperature of 10
℃
and 50
℃
for reconstituted Louiseville clay samples. It is found that as temperature is higher and the strain
rate is smaller, the clay specimen does not follow conventional viscous behaviour, for example, the Isotache model, but the gradient
of stress-strain curve considerably decreases. The reason for different behaviour from the Isotachemodel may be considered to be
attributed to creation of a new structure to resist the external deformation, under high temperature and slow strain rate conditions.
RÉSUMÉ : On considère que le tassement à long terme de dépôts d’argile, appelé consolidation secondaire, est causé par la viscosité
es argiles. Dans cette étude, on examine le comportement visqueux des sols argileux de deux points de vue : celui des effets de la
température et celui des effets de la vitesse de déformation. Afin d’étudier ces effets, on a réalisé sur des échantillons d’argile de
Louiseville reconstitués à des température de 10°C et 50°C un essai oedométrique avec une vitesse de déformation constante
(CRS/Constant Rate of Strain), dans lequel la vitesse de déformation est modifiée durant l’essai. On a constaté que lorsque la
température est plus élevée et la vitesse de déformation plus faible, l’échantillon d’argile ne suit pas le comportement visqueux
conventionnel, par exemple le modèle Isotache, mais que la pente de la courbe de contrainte-déformation plastique diminue
considérablement. On peut considérer que la raison de la différence de comportement par rapport au modèle Isotache doit être
attribuée à la création d’une nouvelle structure pour résister aux déformations externes.
KEYWORDS:clay, one-dimensional consolidation, strain rate effect, temperature effect.
1 INTRODUCTION
In one-dimensional consolidation, the stress-strain relationships
of clayey soils exhibit various viscous behaviours. One of them
is well known behaviour depending on strain rate. It was
reported that the stress-starin relationships of clayey soils were
determined by strain rate (for example, Leroueil et al., 1985;
Tanaka, 2005), and such strain rate effectwas simply described
by Isotache model (Šuklje, 1957).On the other hand, the other
viscous effect related to temperature is also observed. For
example, Eriksson(1989)reported that the consolidation yield
stress (
p’
c
) decreases with an increase in temperature as shown
in Fig.1. These viscous effects, caused by strain rate and
temperature, on stress-strain relationships of clayey soils
arevery similar to each other, and they have been already
reserached in previous studies.However, most of them focused
on either one of the viscous effects: strain rate effect and
temperature effectindividually, not simultaneously.
In this study, combined effects of strain rate and temperature
on consolidation properties of clayey soils are examined.
Especially, temperature effect on compressibility under
smallstrain rate, which is observed in the field, is in detail
discussed.
2 TESTING METHOD AND SAMPLES
In order to investigate combined effects of strain rate and
temperature on consolidationproperties of clayey soils, a special
constant rate of strain (CRS) loading test, in which the strain
rate is changed during the test, was carried out at different
temperatures.To observe the temperature effect, it is preferable
to carry out CRS test using the same specimen, i.e., by changing
the temperature during the testing, to avoid any differences in
soil properties for different specimens. However, changing the
temperature during the testing is very difficult in practice. When
the temperature is changed, the measuring system as well as the
specimen itself is influenced. One example is the zero drift of
the sensors.For this reason, the CRS tests were carried out at
two constant temperatures: 50
℃
and 10
℃
.
Figure 2 shows a schematic view of the CRS testing
apparatus used in this study.The CRS apparatus followed JIS
(Japanese Industrial Standard) A 1227 (2009): the specimen was
60 mm in diameter and 20 mm in initial height.The bottom of
the specimen was connected to a transducer to measure the
water pressure. The applied load was measured by a load cell at
the bottom of the consolidation cell. A back pressure of 100 kPa
was applied to assure good saturation of the specimen during
the test. The effective vertical pressure (
p’
) was calculated
assuming that the excess pore water pressure in the specimen is
distributed in a parabolic manner as expressed by Eq. (1):
2 '
3
p
u
(1)
where,
is the total pressure on the specimen and
u
is the
excess pore water pressure.
A loading apparatus consisted of a Step Motor System
whose resolution is as accurate as 2,621,440 pulses per
revolution, and this was controlled by a personal computer (see
Tsutsumi and Tanaka, 2011).The displacement was not
measured by a conventional dial gauge, but obtained directly by
counting the number of revolutions of the step motor and
corrected by the deformation of the apparatus system. The
