325
Proceedings of the 18
th
International Conference on Soil Mechanics and Geotechnical Engineering, Paris 2013
1
Influence of diatom microfossils on soil compressibility
Influence des microfossiles de diatomées sur la compressibilité des sols
Díaz-Rodríguez J.A., González-Rodríguez R.
Department of Civil Engineering, National University of Mexico, MEXICO
ABSTRACT: There are several sites in the world where diatom microfossils have been detected in the soil deposits (e.g., Mexico
City, Mexico and Osaka Bay, Japan). These soil deposits are characterized to have singular physical and mechanical properties that do
not follow the well established empirical equations relating index properties with strength and deformation parameters. To evaluate
the influence of diatom microfossils on the soil compressibility, this paper presents the experimental results of a series of odometer
tests using artificially prepared mixtures of diatom microfossils and kaolin (D+K). Test results indicate that the presence of diatom
microfossils substantially alters the index properties as well as compressibility.
RÉSUMÉ :
Il ya plusieurs endroits dans le monde où les diatomées microfossiles ont été détectées dans les dépôts de sol (par
exemple, la ville de Mexico, le Mexique et
la baie d’
Osaka, Japon). Ces dépôts de sols se caractérisent par des propriétés physiques et
mécaniques singulières, qui ne suivent pas les équations empiriques bien établies reliant
les propriétés d’
index avec les paramètres de
résistance et de déformation. Pour
évaluer l’
influence des microfossiles de diatomées sur la compressibilité du sol, cet article présente
les rés
ultats expérimentaux d’
une série de tests
d’œ
domètre utilisant des mélanges préparés artificiellement de microfossiles de
diatomées et de kaolin (D + K). Les résultats des tests indiquent que la présence de diatomées microfossiles modifie considérablement
les
propriétés de l’
index ainsi que de compressibilité
.
KEYWORDS: laboratory tests; compressibility; diatomite; kaolinite; mixtures
1 INTRODUCTION
There are several sites in the world where diatom microfossils
have been detected in natural marine and lacustrine soil deposits
(Shiwakoti et al., 2002; Díaz Rodríguez, 2003; Díaz-Rodríguez,
et al.,1998; Terzaghi, et al., 1996).
Natural soils are mixtures of clay particles and coarse-
grained soil constituents, therefore the engineering behavior of a
particulate material, consisting of individuals of a number of
different components (including pores or voids), is in general,
not simply given by the sum of reactions of the single
individuals. Much more important for the whole system is
usually the mutual interactions and interference between these
individuals (particles or grains), which will be influenced by
their spatial arrangement (
i.e
. fabric). The soil fabric and its
close relationship to soil behavior have been studied intensively
by several researchers since many years ago. The level of
participation by different types and sizes of particles within the
soil matrix in the transfer of interparticle contact stresses
dictates the stress-strain behavior.
Soil microstructure is one of the governing factors that are
responsible for the mechanical behaviour of clays.
The
microstructure of soils implies the combined effects of fabric,
chemical composition,
mineralogical constitution,
and
interparticle forces. It is required a greater understanding of soil
microstructure and the contribution of soil particles of different
size to its mechanical response.
This paper addresses the analysis of soil compressibility of
soil mixtures ranging from pure kaolinite to 60% diatomite and
40% kaolinite.
2 DIATOM MICROFOSSILS
Diatomite or diatomaceous earth is a porous and lightweight
sedimentary rock resulting from accumulation and compaction
of diatom remains over a geological time scale. It is a chalk-like
sedimentary rock that is easily crumbled into a fine white to off-
white powder. Diatomite is relatively inert. The typical
chemical composition of diatomite is approximately 90 percent
silica, and the remainder consists of compounds such as
aluminum and iron oxides. It has a high absorptive capacity,
large surface area, low bulk and density. This powder has an
abrasive feel, similar to pumice powder.
Diatoms skeletons or frustules are symmetric in shape and
contain a large proportion of voids. Losic et al. (2007) indicate
that a large percentage (
≈
60 - 70%) of the diatom´s frustules is
essentially void space. Then the intraskeletal pore space of
diatoms provides a chamber which can store water. Although
the intricate frustules of diatoms have been well described, at
the micro- and nano-scales of single cells and their interactions,
interpretations based solely on physical principles have often
been enlightening (Purcell, 1977; Vogel, 1983). Particle-surface
interactions remain poorly understood and can produce
unpredictable or inexplicable results (Feitosa and Mesquita,
1991).
3 ARTIFICIAL MIXTURES OF DIATOMITE AND
KAOLIN
The experimental program followed in this investigation
consisted in the elaboration of six mixtures: diatomite (D) was
mixed with kaolin (K) in proportions of 0% diatomite (100K),
20% diatomite (20D + 80K), 30% diatomite (30D+ 70K), 40%
diatomite (40D+60K), 50% diatomite (50D + 50K), 60%
diatomite (60D + 40K). All mixtures were performed based on
dry weight proportions.
3.1 Material used in mixtures
The kaolin and diatomite used in this investigation are
products commercially available in Mexico. Kaolin is mainly
composed of clay sized particles and soil particles smaller than
