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Liquefaction Susceptibility of Loose Calcareous Sand of Northern Coast in Egypt
La susceptibilité à la liquéfaction du sable calcaire lâche de la côte nord en Égypte
Elmamlouk H., Salem M., Agaiby S.S.
Cairo University, Giza, Egypt
ABSTRACT: This research studied the liquefaction susceptibility of calcareous sand encountered at the North Coast of Egypt. The
study was carried out through a series of cyclic isotropically consolidated undrained triaxial tests, complemented by a suite of
physical characterization and index tests. A total of nine (9) cyclic loading tests were conducted on samples prepared at initial relative
density of 40%. The variables considered herein included the cyclic stress ratio and initial effective confining stress. The resulting
pore-water pressure generation and liquefaction resistance trends for the North Coast calcareous sand were compared to other
calcareous and siliceous sands reported in the literature. The test results indicated that the compressible soil skeleton of the North
Coast calcareous sand did not result in lower cyclic strength and that the tested sand is less susceptible to liquefaction compared to
siliceous sands reported in the literature. This increase in cyclic strength is likely to be the result of the angularity of the calcareous
sand particles. Relationship between cyclic resistance ratio and effective confining pressure was developed for the studied relative
density.
RÉSUMÉ : Dans cette étude, la susceptibilité à la liquéfaction du sable calcaire rencontré à la Côte Nord de l'Égypte a été investiguée.
L'étude a été réalisée à partir d’une série d’essais triaxiaux consolidés non drainés cycliques isotrope, en addition à une série de tests
de caractérisation physique et des indices. Neuf (9) essais de chargement cycliques ont été effectués sur des échantillons préparés à un
indice de densité relative initiale de 40%. Les variables considérées ici comprennent le rapport de la contrainte cyclique et la
contrainte initial de confinement. Les pressions interstitielles et la résistance de liquéfaction résultantes du sable calcaire de la Côte
Nord ont été comparées à d'autres sables calcaires et siliceux rapportés dans la littérature. Les résultats des tests ont indiqué que le
squelette du sol compressible de la Côte Nord du sable calcaire n'a entraîné aucune réduction de la capacité cyclique et que le sable
testé est moins susceptible de se liquéfier par rapport aux sables siliceux rapportés dans la littérature. Cette augmentation de la
capacité cyclique est susceptible d'être le résultat de l'angularité des grains de sable calcaire. La relation entre le rapport de résistance
cyclique et la contrainte effective de confinement a été développée pour l’indice de densité relative étudié.
KEYWORDS: Loose Calcareous Sand – Cyclic Loading – Triaxial – Liquefaction.
1 BACKGROUND
Calcareous sands result from various biological, mechanical,
physical, and chemical depositional environments (Coop and
Airey, 2002). As a result, it was found that there are two main
reasons behind the difference in their behavior compared to
other siliceous sands subjected to similar loading conditions.
First, calcareous sand has remarkable intra-particle void space
(within the particles), which is mainly caused by the particles
being made of shells and corals that include cavities inside their
bodies (Hyodo et al., 1998; Coop and Airey, 2002; and Sharma
and Ismail, 2006). Second, the angular particle shape of this
sand found in various forms such as curved flat particles from
fragments of sea shells or hollow tube-shaped particles from
remains of skeletons of small marine organisms, which explains
the remarkable inter-particle space (between particles). Both
reasons lead calcareous sands to be more compressible with
higher susceptibility to crushing upon stressing compared to
siliceous sands. Different particle breakage factors have been
suggested to quantify the particle breakage upon loading; these
breakage factors are empirical and depend mainly on changes in
particle sizes (Hardin, 1985; and Lade et al., 1996).
Common soil classification systems (such as the Unified Soil
Classification System) do not distinguish between calcareous
and non-calcareous sands. Classification of calcareous
sand/gravel has been proposed by Hallsworth and Knox (1999)
to reflect the grain size of particles as well as the composition of
carbonates forming the particles. Void ratios in siliceous sands
typically vary from 0.43 to 0.85; while for calcareous sands,
minimum and maximum void ratios range from 0.54 to 1.62,
and maximum void ratios range from 0.71 to 1.98. Specific
gravity of minerals composing calcareous soils like calcite is
2.75 and aragonite is 2.95 (Hurlbut, 1971). On the other hand,
siliceous minerals are less heavy, since they typically include
quartz with a specific gravity value of about 2.65. Specific
gravities for calcareous sands typically range from 2.71 to 2.86,
while that for siliceous sands can be less than 2.65 (Hyodo et
al., 1996; Morioka, 1999; and LaVielle, 2008).
Different approaches have been reported in the literature to
evaluate liquefaction susceptibility of soils subjected to cyclic
loading, among which studying the number of cycles to failure
versus Cyclic Stress Ratio (CSR). CSR is defined as the ratio of
the applied cyclic shear stress to the initial effective confining
pressure (σ′
c
). The effects of CSR and σ′
c
on liquefaction
susceptibility of siliceous and calcareous sands reported in the
literature are presented in this paper. In Egypt, calcareous sand
is common along the Northern Coast. This study aims at
assessing cyclic behavior of this sand to make a better
assessment of the liquefaction susceptibility through a
laboratory experimental program.
2 MATERIALS AND EXPERIMENTAL METHODS
The tested calcareous sand was obtained from the near surface
of a site located at about km 135 Alexandria – Matrouh road,
North Coast, Egypt. The sand has sub-angular to angular grains
with light tan to white color. The tested sand has grain sizes
