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Water injection aided pile jacking centrifuge experiments in sand
Essais en centrifugeuse d’installation de pieux vérinés dans le sable avec injection d’eau
Shepley P., Bolton M.D.
University of Cambridge
ABSTRACT: Jacked piles have several advantages over conventional piling techniques; namely the low noise and vibration output
from the process. However they are often difficult to install in hard ground conditions. A supplementary water injection technique
can be used to reduce installation loads. Water is injected from the pile toe at high pressure and flow rates into the ground, achieving
large reductions in installation loads. In this research, water injection aided pile jacking was modelled on a geotechnical centrifuge.
A dense, fine sand was used and multiple pile installations were completed in order to investigate the effect water injection has on
installation loads. To complete the modelling, a high water pressure supply for use on the centrifuge was developed and systems to
maintain centrifuge balance were implemented. This paper also identifies and validates a method for calculating pressures of interest
based on the limited measurement locations available.
RÉSUMÉ : L’installation des pieux vérinés présente plusieurs avantages comparativement aux techniques de pieux conventionnelles,
en particulier cette méthode est peu bruyante et génère de faibles vibrations. Cette technique est par contre difficile dans les sols
denses et compacts. L’injection d’eau supplémentaire permet de réduire les charges d’installation. L'eau est injectée au niveau de la
base des pieux dans le sol sous forte pression et à haut débit, ce qui permet une réduction importante des charges d’installation. Dans
cette étude, l’installation des pieux vérinés assistée par injection d’eau a été modélisé dans une centrifugeuse géotechnique. Un sable
dense et fin a été utilisé et de nombreuses installations de pieux ont été réalisées pour évaluer l'effet de l'injection d'eau sur les charges
d'installation. Pour compléter la modélisation, une nouvelle alimentation d'eau sous haute pression pour utilisation en centrifuge a été
développée et un système de maintien de l'équilibre de la centrifuge a été implémenté. Cette recherche identifie et valide également
une méthode de calcul des pressions d’intérêt basée sur des localisations de mesure limitées sur le terrain.
KEYWORDS: jacked pile, centrifuge, sand, water jetting, water injection
1 INTRODUCTION
Jacked, or silent, piling is an increasingly important method for
pile installation. Construction projects in urban or sensitive
areas desire a low-impact means of installing pile walls or piled
foundations. This is due to their low disruptive nature –
producing little noise and few ground vibrations (White et al.
2000). In addition, they often require fewer enabling works due
to the smaller machinery (Goh et al. 2004).
However, jacked piles are restricted by the maximum
deliverable installation force. Often this is limited by the
available kentledge for counterweight systems. In the case of
the jacked piling system produced by Giken Seisakusho Ltd., a
Japanese piling contractor, reaction force is provided by the
previously installed piles in the pile wall. Three or four piles
are used in tension to provide the installation load for the
subsequent pile. In this case the load limit is set by the
capability of the machine, not necessarily the available reaction
force. In all cases, if the piling load approaches the load limit of
the machine, the installation rate may fall to an uneconomical
level or even pile refusal.
To reduce or prevent these situations, a supplementary
installation technique can be used. The aim of any such
technique is to maintain the advantages of the installation, with
low noise and vibration levels, but also reduce the installation
load so that piles can be jacked into hard ground. Many
techniques exist to achieve this, such as surging, pre-augering
and gyropiling. However, the use of a supplementary water
injection during the pile installation to reduce the installation
forces is of particular interest for this study.
Modelling of the water injection technique has been
completed using the Turner Beam Centrifuge at University of
Cambridge. A high pressure water supply was developed for
use on the centrifuge in order to replicate the high water
pressures and flow rates experienced in the field. This paper
will outline the current use of the technique, in addition to the
centrifuge modelling completed.
2 DEVELOPMENT OF WATER INJECTION
Water jetting has been in common use for decades, mainly for
offshore pile installation (Tsinker 1988). The offshore setting
provides a large water source and no nearby structures that may
be affected or damaged. Typical flow rates for this early
technique exceeded 1500 litres per minute in all soil types. In
addition, water jetting was found to be disruptive to the soil
fabric around the installed pile. The ground was liquefied so
that the pile could be installed under self weight. This resulted
in global particle rearrangement where large particles sank to
the bottom of the pile installation.
The technique has since been improved to allow its more
widespread use. Required flow rates were reduced to below
1000 litres per minute following a review from Tomlinson and
Woodward (2008).
If the water jetting technique is used in conjunction with
another pile installation method – pile jacking with
supplementary water injection, then the flow rates can be
