2957
Case Study on X-section Cast-in-place Pile-Supported Embankment over Soft Clay
Étude de cas pour un remblai renforcé par des pieux de section en X coulés en place dans de
l’argile molle
Liu H.L., Kong G.Q., Ding X.M, Yu T., Yang G.
Key Laboratory for Ministry of Education for Geomechanics and Embankment Engineering, College of Civil and
Transportation Engineering, Hohai University, Nanjing, Jiangsu, P. R. China
ABSTRACT: Pile-supported embankments are widely used for highway, railway, seawall, etc. over soft soils because of their
effectiveness in minimizing deformation and accelerating construction. A new method of using X-section cast-in-situ concrete piles
(referred to as XCC pile) which can improve bearing capacity, reduce settlement and costs effectively for foundations over soft clay is
developed by Hohai University of China. In this paper, construction method, quality assurance (QA), and quality check (QC) involved
in this method are described. A large-scale model test program on a XCC pile and a circular pile, both constructed with the same
amount of concrete volume, was carried out to obtain the load transfer behavior of both piles under three different loading modes:
compression, uplift, and lateral loads. One XCC pile-supported embankment application was presented. The large -scale load test
indicated that load carrying capacity of XCC pile is slightly higher than that of circular pile, when the same amount of concrete
volume was used. It is worth pointing out that this XCC pile type can be constructed rapidly, quality assurance (QA) and quality
checked (QC) easily, and cost-effectively. The results of this study can provide reference for practical XCC pile-supported
embankment design and construction.
RÉSUMÉ : Les remblais renforcés par pieux sont largement utilisés pour les autoroutes, les voies de chemin de fer, les digues, etc
…construites sur des sols mous en raison de leur efficacité à minimiser les déformations et à accélérer la construction. Une nouvelle
méthode développée par l’Université de Hohai en Chine consiste à utiliser des pieux en béton de section en X coulés in situ (appelés
pieux XCC) qui peuvent améliorer la capacité portante, réduire efficacement le tassement et les coûts pour des fondations dans de
l’argile molle. Dans cet article, méthode de construction, assurance qualité (AQ) et contrôle de qualité (QC) impliqués dans cette
méthode sont présentés. Un programme d'essai sur des modèles à grande échelle avec un pieu XCC et un pieu circulaire, construits
avec la même quantité de béton, a été réalisé pour obtenir le comportement de transfert de charge pour les deux pieux sous trois
modes différents de chargement : compression, soulèvement et latéral. Une application pour un remblai renforcé par des pieux XCC
est présentée. Le test de chargement à échelle réelle indique que la capacité portante du pieu XCC est légèrement supérieure à celle du
pieu circulaire, pour la même quantité de volume de béton. Il est intéressant de souligner que ce type de pieu XCC peut être construit
rapidement avec des assurances qualité (AQ) et contrôles de qualité (QC) faciles et à moindre coût. Les résultats de cette étude
peuvent servir de référence dans la pratique pour la conception et la construction des remblais renforcés par les pieux XCC.
KEYWORDS: XCC pile, pile supported embankment, soft clay, case study.
1 INTRODUCTION.
Pile-supported composite foundation is one of useful soft soils
treatment methods. It is widely used to construct highways,
railways, and seawall on soft soils due to their rapid
construction, small total and differential deformations, and low
costs compared to other traditional soft soils improvement
methods (such as, deep cement mixing (DCM) piles (Arulrajah
et al
. 2009), stone columns (Gniel
et al
. 2009), and precast
prestressed piles (Han & Gab 2002; Dzhantimirovk
et al
. 2009;
and Bakholdin
et al
. 2009)). Many cases using pile-supported
embankments, such as, the railway widening projects (Jones et
al. 1990; and Eekelen & Bezuijen 2008), the retaining wall
projects (Alzamora et al. 2000), the vertical wall breakwaters
(Suh
et al
. 2006), and the freeway embankment in USA and
China
(American
Association
of
State
Highway
Officials/Federal Highway Administration 2002; Liu
et al
.
2009; and Chen
et al
. 2010
a
).
There are some ways to optimization pile-supported
composite foundation designs by coordinating load share ratio
of pile-soil. Special shape piles can improve the contact areas of
pile-soil interface and lateral stiffness in specific direction
effectively, which means the friction of pile shaft, and lateral
load capacity can be improved in the same concrete
consumption. It can coordinating load share ratio of pile-soil
more suitable. Barrette pile (Lei
et al
. 2001), H-pile (So
et al.
2009), and steel pipe pile (Arulmoli
et al
. 2010) etc, are widely
used for pile foundation. While these special concrete piles have
low costs and are more suitable for soft soils treatment. Y-
section cast-in-situ concrete pile use for pile-supported
embankment is reported (Chen
et al
. 2010
b
), while the lateral
stiffness of these piles is not easy to control.
Hence, this paper presents one new method of soft soils
treatment: XCC pile-supported composite foundation method.
The construction method, quality assurance, and quality check
involved in this method are described. A large-scale model test
program on a XCC pile and a circular pile, both constructed
with the same amount of concrete volume, was carried out to
obtain the load transfer behavior of both piles under three
different loading modes: compression, uplift, and lateral loads.
A case study that illustrates the application of this method in a
pile-supported composite foundation over soft clay is presented.
The pile shaft of XCC pile are measured and analyzed.
2 CONSTRUCTION METHOD
Cast-in-situ rather than precast concrete X-section piles are
used. This is because it is difficult to transport and install X-
section piles without affecting the integrity of the pile,
particularly when the piles are not reinforced in the corner part
of piles. For this purpose, a special pile driving machine and
