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Dynamic soil-pile behavior in liquefiable sand overlaid with soft clay
Dynamiquesol-pieucomportementdans le sableliquéfiablerecouvert d'argile molle
Ghotbi S.M.A
.
, Olyaei M., Yasrebi S.S.
Associate Professor, Tarbiat Modares University
Mosallanejad M.
Assistant Professor, Shiraz University
ABSTRACT: A lot of structures are constructed in the vicinity of river streams or sea shores among which bridges, wharves and wind
turbines are of more importance. Soil covering these regions is generally constituted of sedimentary loose sand and very soft clay. For
this reason, pile foundations are typically used to support the structures and transfer loads to deeper and denser soil. Saturated loose
sands which have low relative densities are suspected to liquefy during dynamic loadings like earthquakes. The effect of soft clay
overlaying sandy soil is also some sort of questionable during liquefaction. In this study, a 3D model is used to investigate the soil and
pile response during liquefaction using FEM method. The constitutive model is based on multi-surface plasticity framework and is
capable of predicting sand behavior in undrained condition. Soil response is investigated under some aspects like loading frequency
and presence of clayey layer. Pile behavior in terms of pile bending moment is also discussed. It can be concluded that loading
frequency and presence of clay layer can have serious effects on pile responses.
RÉSUMÉ : Un grand nombre de structures sont construites à proximité des cours d’eau ou sur les rives de la mer dont les ponts, les
quais et les éoliennes sont plus importantes. Les sols dans ces régions sont généralement constitués de sable et d’argile sédimentaire
meuble très doux. Pour cette raison, les fondations sur pieux sont généralement utilisées pour soutenir les structures et les charges de
transfert aux sols plus profonds et plus denses. Les sables saturés et lâches qui ont de faibles densités relatives sont soupçonnés de se
liquéfier sous charges dynamiques telles que les tremblements de terre. L’effet des superpositions d’argile et de sable fin du sol est
étudié lors de la liquéfaction. Dans cette étude, un modèle 3Dest utilisé pour étudier le sol et apporter une réponse lors de la
liquéfaction en utilisant la méthode des éléments finis. Le modèle constitutif est basé sur le cadre plasticité multi-surface et est
capable de prédire le comportement du sable dans un état non drainé. La réponse du sol est étudiée sous certains aspects tels que la
fréquence de chargement et la présence de la couche argileuse. Le comportement des pieux en moment de flexion pile est également
discuté. On peut en conclure que la fréquence de chargement et la présence d’une couche d'argile peuvent avoir des effets graves sur
les réponses de pieux.
KEYWORDS: Soil-Pile interaction, Liquefaction, Dynamic Loading, Multi-Surface constitutive model.
1 INTRODUCTION
Structures constructed at marine areas and river vicinities are
endangeded by liquefaction during dynamic loading and
specially earthquakes. Some cases of such extensive destruction
of structures are observed during earthquakes of Niigata(1964),
Alaska(1964), Loma-Prietta(1989) and Kobe (1995). An
example of damages to wharf piles caused by liquefaction is
shown in Figure 1.
Figure 1.Bending and displacement of pile foundation at Puerto de
Coronel Muelle wharf.
The liquefaction mechanisms can be classifed into two main
categories: 1) Flow Liquefactin 2) Cyclic Mobility.According to
Ishihara (1997), it can be concluded that two types of lateral
loading is applied to a pile during an earthquake: 1)Inertial
foces 2)Kinematic forces. Inertial forces are applied from
superstructure to the pile head and their frequency is a function
of structure and the earthquakedominant frequency. Inertial
forces are largest before liquefactin and are intensely decreased
after the soil is liquefied. Kinematic forces are applied to pile
due to the displacement of liquefied soil and they become larger
if the ground is inclined or a non-liquefiable layer is overlaid
on the liquefiable layer.
Although a lot of research has been carried out to study the
liquefaction phenomena and its effect on structures, it can be
mentioned that there are some aspects relating to pile response
which need to be more clarifiedby utilization of experimental
and numerical methods.In the case of experimental studies,
some noteable recent works are mentioned briefly. Wilson et al.
(1998)accomplished a series of centrifuge tests on piles and
their superstructures in liquefiable soil. They observed that
sesmic response of soil-pile-superstructure is related to soil
type, nature of earthquake and the soil displacements. Other
physical test to be noted are Komijo et al. (2004), Yao et al.
(2004), Tokimatsu et al. (2005), Dunga et al. (2006), Tamura &
Tokimatsu (2005), Han et al. (2007) and Haeri et al. (2012).
Some important numerical studies include Finn et al. (2001),
Tabesh & Poulos (2001), Miyazaki et al. (2001), Fujita and Finn
(2002), Klar et al. (2003), Liyanapathirana & Poulos (2002,
2005), Chang et al. (2007), Bhattacharya et al. (2008), Zhang &
Jeremic (2009) and Rahmani & Pak (2011). In many of the
numerical studies mentioned above, asoil fluid formulation with
uncoupled aproach is used. Furthermore, previously used
constitutive models are generaly very simple. These can lead to
inacurate results in some cases. Also, some aspects like effect of
Comportement dynamique sol-pieu dans un sable liquéfiable surmonté par de l’argile molle
