2703
Proceedings of the 18
th
International Conference on Soil Mechanics and Geotechnical Engineering, Paris 2013
Dynamic Pile Testing at the Mesa A Rail Bridge
Analyse dynamique
d’essais
de pieux au pont ferroviaire Mesa A
Jonathan G Cannon
Independent Geoscience Pty Ltd, Melbourne, Australia,
ABSTRACT: The paper will describe high strain and low strain dynamic pile testing that was used to assess the foundations for this
bridge and how the results led to an innovative decision during construction to change from a bored pile foundation to a driven pile
foundation. The revised construction used minimal extra equipment and materials. The foundations originally comprised
permanently cased bored piles socketed into rock. Dynamic pile testing identified significant problems with the concrete early in the
project. A number of attempts were made to correct the problems but to no avail. In addition, the down-the-hole hammer system
being used to install the casings was causing delays. The steel tube casings being used were substantial and a large hydraulic piling
hammer was on site for dynamic testing. A decision was made to drive the casings into soft rock far enough to generate the required
compression and tension resistance and to delete the concrete sockets. Dynamic pile testing was used to verify that the required
resistances were achieved.
RÉSUMÉ : Cet article décrit l'analyse dynamique d
’essais d
e pieux sous forte et sous faible déformation, effectuée pour évaluer les
fondations du pont, et montre comment les résultats ont mené à une décision innovante pendant la construction, passant de fondations
par pieux forés à des fondations par pieux foncés. Le changement de construction nécessita peu d'équipements et matériaux
supplémentaires. Les fondations comprenaient à l'origine des pieux forés dans la roche maintenus de manière permanente par des
conduites en béton. L'analyse dynamique des pieux mit en évidence un sérieux problème lié au béton dès le début du projet. Plusieurs
tentatives pour le régler furent infructueuses. De plus, le système de marteau de fond de trou utilisé pour installer les pieux posait
problème et créait des retards. Les conduites en acier utilisées étaient de grande taille et un marteauhydraulique était sur place. La
décision fut prise d'enfoncer les boitiers dans une roche meuble assez profondément pour générer la compression et tension
nécessaires et de supprimer les conduites en en béton. L'analyse dynamique de pieu fut ensuite utilisée pour vérifier que la résistance
nécessaire était atteinte.
KEYWORDS: Dynamic pile testing, Bridge Foundations, PDA, CAPWAP, Cross-Hole Sonic Logging, PIT, WEAP.
1 INTRODUCTION.
The Mesa A bridge is located over the Robe River in the Pilbara
Region of Western Australia. Iron ore is mined from various
Mesa, or low flat-topped mountains, in the area. The iron ore is
carried directly from near the mine face by rail to a processing
and export facility about 200km away. The trains are some of
the longest in the world and have some of the highest axle loads
in the world. At the bridge site the Robe River is dry on the
surface for much of the year but up to 15m deep and fast-
flowing during the "wet" cyclone season. Significant scour of
the foundations was expected. High lateral loading from river
debris was also anticipated.
During the "dry" construction season conditions are
arduous for construction work and, in particular, concreting
with daytime temperatures typically 38-42° C and within the
construction zone in the low-lying riverbed they were frequently
higher.
The Specification for the work included a test pile
separate from the bridge works, which was to be tested
statically in tension, together with testing for integrity using
cross-hole sonic logging (CSL). The contractor offered high
strain dynamic testing with a Pile Driving Analyzer
®
(PDA) as
an alternative to the static test. The client required PDA testing
at 40kHz, which required the newest PAX model PDA.
2
FOUNDATION CONDITIONS
Foundation conditions comprised saturated gravels and cobbles
over an extremely low to very low strength weathered shale.
The depth to top of rock varied from 10m at the West Abutment
to 23m at the East Abutment. Although surface water rarely
flowed during the "dry" season the ground water was near
surface level and was flowing through the gravels and cobbles.
Surface pools were evident a short distance downstream from
the site. An extensive site investigation was conducted with at
least one borehole at each pier location and sometimes two.
The shale rock strength was variable and was logged as
being of UCS about 0.4 to 1.0MPa, with some harder siliceous
bands and quartz intrusions. There were also bands that were
completely weathered to a stiff clay.
3
INITIAL CONSTRUCTION METHOD
The Contractor submitted alternative pier foundations that
comprised three raking piles in a tripod arrangement as shown
below. (Figure 1). The tripod arrangement meant there were no
redundancies and it was absolutely essential for every pile to
perform as designed. Abutment foundations comprised four
vertical piles. The size of the abutments meant there was the
possibility of installing extra piles to augment any under-
strength piles.
Cannon J.G.
