2823
Identification of Test Pile Defects in a Super-tall Building Foundation
Identification des anomalies dans les essais de chargement de pieu pour les fondations d'une tour
de très grande hauteur
Poulos H.G.., Badelow F.
Coffey Geotechnics
Tosen R.
Rio Tinto Copper Projects
Abdelrazaq
Samsung C&T Corporation
Kim S.H.
Jinyoung ENC Enterprise
ABSTRACT: As part of the foundation design verification process for a super-tall tower in South Korea, a program of pile load
testing was initiated. The test program involved vertical load tests on four piles and a lateral load test on two piles, jacked against each
other. The vertical load tests used the Osterberg cell method, with two sets of Osterberg cells installed in each pile, one near the pile
base, and the other about 6m above the base. In addition to the vertical load tests, sonic tubes were installed in the test piles to
examine the integrity of the constructed pile. The sonic tube testing revealed defects in one of the test piles, and the behaviour of this
pile under load was found to have a number of anomalies. This paper sets out the process by which the defects were identified, and
approach used to interpret the sonic logging data to produce tomographic images of the pile along its length. The consequences of the
defects and the irregularities in pile diameter on the inferred distribution of load along the pile are also described.
RÉSUMÉ : Dans le cadre du processus de vérification de la conception des fondations d’une tour de très grande hauteur en Corée du
Sud, un programme d’essais de de chargement de pieux a été entrepris. Le programme d’essais implique des essais de chargement
vertical sur quatre pieux et des essais de chargement latéral sur deux pieux, vérinés l’un à l'autre. Les essais de chargement vertical
utilisent la méthode d’Osterberg, avec deux jeux de cellules d’Osterberg installés dans chaque pieu, un près de la base et l'autre
environ 6 m au-dessus de la base. En plus des essais de chargement vertical, des tubes acoustiques ont été installés dans les pieux pour
examiner leur intégrité. Les essais acoustiques ont révélé des défauts dans l'un des pieux testé, et le comportement de ce pieu sous
charge présentait un certain nombre d'anomalies. Cet article décrit le processus par lequel les défauts ont été identifiés, et l’approche
utilisée pour interpréter les données d'enregistrement acoustique pour produire des images tomographiques du pieu sur toute sa
longueur. On décrit aussi les conséquences des défauts et des irrégularités du diamètre du pieu sur la distribution présumée de charge
le long du pieu.
KEYWORDS: analysis ; defects; foundations ; integrity testing ; piles ; tall buildings.
1. INTRODUCTION
Figure 1 illustrates the proposed 151 storey Incheon Tower,
which is located in district 8 of the Songdo Incheon Free
Economic Zone in South Korea. The site lies entirely within an
area of reclamation underlain by up to 20m of soft to firm
marine silty clay, which in turn overlies residual soil and a
profile of weathered rock, which is underlain by a better quality
rock referred to as “soft rock”. The tower is composed of
approximately 30 storeys of office floors, 8 storeys of hotel and
other supporting facilities, 100 storeys of residential floors, and
several levels of mechanical plant. The base of the tower
consists of retail, a future subway station, and several levels of
parking. It is anticipated that the total area of the tower and the
base for Phase 1 construction will be approximately 412,000
m
2
. The structural system of the tower in the east-west direction
consists of a reinforced concrete core wall system linked to the
exterior mega columns with reinforced concrete or composite
shear panels. The tower superstructure is founded on a pile
supported raft foundation. The 5.5 m thick reinforced concrete
raft is supported on a total of 172 bored piles, 2.5 m in diameter,
with variable lengths, extending 5 m into the soft rock for added
stiffness and axial load capacity. Details of the geotechnical
conditions and the foundation design are given by Abdelrazaq et
al (2011).
2. PILE LOAD TESTING
Introduction
As part of the final design process, five pile load tests were
undertaken, four on vertically loaded piles via the Osterberg cell
(O-cell) procedure, and one on a laterally loaded pile jacked
against one of the vertically loaded test piles. For the vertical
pile tests, two levels of O-cells were installed in each pile, one
at the pile tip and another at a level between the weathered rock
layer and the soft rock layer.
Figure 1. 151 storey Incheon Tower – Architectural Rendering
