3227
Effect of dredge soil on the strength development of air-foam treated lightweight soil
Effets des sols de dragage sur le développement de la résistance des sols mélangés à de l’air
Kataoka S.
Hakodate National College of Technology, Hakodate, Japan
Horita T.
Kobe University, Kobe, Japan
Tanaka M.
Port and Airport Research Institute, Yokosuka, Japan
Tomita R., Nakajima M.
Koa Kaihatsu Corporation, Chiba, Japan
ABSTRACT: In this study, the unconfined compression strength,
q
u
, and the elastic shear modulus,
G
, from bender element test, were
in detail examined in the laboratory by using the air-foam treated lightweight soil samples made from several kinds of soil. From the
results of these tests, the values of the
q
u
and the
G
with curing period were different to the kinds of soils into the air-foam treated
lightweight soil samples. In addition, it was found that the development of the
q
u
and the
G
were related to the increase / growth of the
ettringite produced at the time of the reaction of hydration of the concrete. On the other hands, it has been shown that the relations
between the
q
u
and the
G
are nearly proportional, and that this tendency remains always the same, whatever is the type of soil.
RÉSUMÉ : Dans cette étude, la résistance en compression simple,
q
u
, avec le module d'élasticité de cisaillement,
G
, du critère de
l'élément bender, était en détail examinés en laboratoire à l'aide de l'air sous forme d'échantillons de sol traités légers fabriqués à partir
de plusieurs types de sols. A partir des résultats de ces tests, les valeurs de la
q
u
et le
G
avec période de cure étaient différents des
types de sols dans l'air sous forme d'échantillons de sol traité légers. En outre, il a été constaté que le développement de la
q
u
et le
G
sont liés à l'augmentation / la croissance de l'ettringite produite au moment de la réaction d'hydratation du béton. Dans le cas contraire,
il a été montré que les relations entre la
q
u
et le
G
sont presque proportionnelle, et que cette tendance reste toujours le même, quel que
soit le type de sol.
KEYWORDS: air-form treated lightweight soil, unconfined compression strength, elastic shear modulus.
1 INTRODUCTION
Air-foam treated lightweight soil is a ground material prepared
by adding and mixing in a cement-type stabilizing agent and air
foam made by a surfactant or animal-protein foaming agent to a
source soil such as dredged soil and surplus construction soil. In
recent years, there has been an increase in the number of
construction projects using air-foam treated lightweight soil for
the purpose of reducing earth pressure and containing land
subsidence. This new type of ground material for harbor and
airport construction that offers added value such as light weight,
safety, and recyclability is called Super Geo-Material (SGM)
(e.g. Thuchida et al. 1996).
When SGM is employed for a construction site, the required
strength of the mix proportion is obtained by multiplying the
design strength by an overdesign factor, and a mix proportion
test is conducted in advance to determine the amount of
stabilizing agent and air foam to be added to the source soil of
which the moisture content has been adjusted with water. In
some cases where the physical properties of the source soil are
expected to vary from one sampling location to another, a mix
proportion test is conducted in advance for each representative
sampling location to adjust the amount of additives. Naturally,
some variations are found in the strength of the soil samples
(Nagatome et al. 2010). In fact, when the unconfined
compression test and the bender element (BE) test were
conducted on a large number of SGM samples taken from the
same construction site and to which an equal amount of the
stabilizing agent had been added, the unconfined compressive
strength,
q
u
, varied from one sample location of the source
dredged soil to another, albeit within the expected range of the
design. It was confirmed that there is a high correlation between
the shear wave velocity,
V
s (or shear modulus,
G
) and
q
u
(Kataoka et al. 2011).
This study focused on the properties of the source soil within
SGM. Six different types of source soil were used to prepare
SGM in a room environment. The unconfined compression test
and the BE test were conducted to examine the impact of curing
time on the strength and stiffness of the soil. In addition, the
microscopic structure of the specimens was observed using a
Scanning Electron Microscope (SEM) in order to visually
examine how the internal structure of SGM changed with the
curing time.
2 SAMPLE PREPARATION AND TESTS PERFORMED
Table 1 shows the physical properties of the source soils used to
prepare the SGM specimens. Six types of source soil were used:
two types of dredged soil taken from the construction site of the
Tokyo International Airport expansion project, one from the
area where the odor of what was suspected to be hydrogen
sulfide, biological decay and the like (hereafter “Tokyo Bay A”)
was relatively weak and the other from the area where the same
odor was very strong (hereafter “Tokyo Bay B”); dredged soil
taken from Kobe Port (hereafter “Kobe”); surface soil taken
from a few meters below the seabed of the Sea of Okhotsk
(hereafter “Okhotsk”); Kasaoka Clay; and Kuni-bond. The latter
two are commercially available products. When liquid limit,
w
L
,
a criterion used for the mix proportion design, was examined,
the six types of source soil could be categorized as follows:
Tokyo Bay A and B and Kobe, which had an approximately
equal level of liquid limit; Kuni-bond, which had a higher
w
L
than the aforementioned three types; and
Okhotsk Seabed
Sediment and Kasaoka Clay, which had a lower
w
L
.
While there
were almost no differences between Tokyo Bay A and B in
physical properties such as
w
L
and grain size composition, a
major difference was observed in the pH level of pore water.
