NUI Galway – UL Alliance First Annual ENGINEERING AND - ARAN ...

Axial Load Capacity of a Driven Cast-in-Situ Pile in Mixed Ground
Conditions
Mr. Kevin Flynn and Dr. Bryan McCabe
College of Engineering and Informatics, NUI Galway
k.flynn8@nuigalway.ie
Abstract
Driven cast-in-situ (DCIS) piles are used extensively
in piling projects in the UK. Due to the lack of
knowledge on the axial load behaviour of DCIS piles, a
static load test was conducted on an instrumented pile
in mixed ground conditions at Pontarddulais, Wales.
The test results showed that the pile was influenced by
residual load due to curing which significantly altered
the load distribution at failure.
1. Introduction
Driven cast-in-situ (DCIS) piles are classified as a
type of displacement pile [1]. The installation process
involves driving an open-ended steel tube with an
expendable driving shoe. Upon reaching the required
depth of penetration, the reinforcement is inserted into
the tube, followed by concreting via a skip. The tube is
then withdrawn and the concrete is left to cure in-situ
for a number of days. Despite the popularity of DCIS
piles, there is a surprising lack of literature on their axial
load behaviour. A static load test was performed on an
instrumented DCIS pile in order to assess the axial load
behaviour as part of an overall study to estimate pile
capacity based on measurements during installation.
2. Ground Conditions
The ground investigation consisted of 3 no. cone
penetration tests (CPT) at the pile test location. Each
test was specified to penetrate to a minimum depth of 10
m. The tests revealed mixed ground conditions
consisting of 1.5 m of dense fill overlying 3 m of soft
clay, followed by 1.5 m of medium dense silty sand. A
1.2 m layer of firm clay was encountered at 6 m,
followed by sand of varying density to a depth of 10 m.
The water table was located at 2 m below ground level
according to borehole reports.
3. DCIS Test Pile
The DCIS test pile was 340 mm in diameter and 8.5
m in length. The pile was instrumented with 16 no.
vibrating wire strain gauges in order to obtain the load
distribution during testing. Strain readings were taken
before and after installation of the reinforcement, and
immediately prior to commencing the pile load test.
Analysis of the readings revealed that the pile was
experiencing significant tensile strains as a result of
swelling during curing, which results in the
development of residual load [2].
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4. Static Load Test
A static load test was conducted approximately 9
days after pile installation. The pile was subjected to
three loading/unloading cycles, with failure occurring at
a load of 935 kN. The strain gauges enabled the load
distribution along the pile at failure to be obtained
(Figure 1). The distribution was significantly affected
by the residual load which developed during curing,
with the base resistance accounting for approximately
31 % of the ultimate load.
Figure 1 - Load distribution in DCIS test pile at failure
6. Conclusions
The concrete curing process for DCIS piles results in
the development of residual load which alters the load
distribution obtained from a static load test.
7. Acknowledgements
The authors wish to acknowledge Keller Foundations
UK for sponsoring this research project.
8. References
[1] Tomlinson, M, Pile Design and Construction Practice,
Taylor & Francis, 1994.
[2] Kim, M., Cavusoglu, E., O’Neill, M., Roberts, T. and Yin,
S, “Residual load Development in ACIP Piles in a Bridge
Foundation”, GeoSupport 2004, pp. 223-235.