||Grafton Bridge Strengthening
||Auckland City Council
||Brian Perry Civil
||Grafton Bridge Auckland CBD
||January - May 2009
||Drill piers for installation of reinforcement
Grafton Bridge was to be strengthened and repaired for further use as part of the Newmarket – Britomart Busway. This landmark bridge has just turned 100 years old and was the largest single arch concrete bridge in the world when built. In order to reach 200 years it needed a bit of TLC and strengthening.
The scope of work Lowery undertook included:
• Drilling 76mm and 102mm diameter holes vertically down the inside of the piers for installation of reinforcement up to 16m deep
• Drilling 250mm diameter x 4m deep in pier foundations for new mini piles to increase its loading capacity
Tight drilling tolerances of 2mm/m were achieved and bettered in the old concrete where voids and loose material severely tested the drilling crews, drilling tips were broken and lost, and part grouting had to be done to enable some of the holes to achieve full depth. Adding to the challenges were the occasional vertical railway line, pieces of timber and large basalt rocks thrown in to displace the volume of hand mixed concrete.
The two drilling machines used were Lowery produced self feed hydraulic rigs with our own developed tooling and taking 2m passes.
Since the piers were below the roadway, holes were drilled through the deck before the machines could be aligned on top of the piers 1200mm further down. Slurry protection consisted of a water tight box built on the pier head and a submersible pump alongside the drill string pumping to a reservoir on the deck that was periodically emptied via one of our vacuum trucks.
Grafton Bridge reopened on Labour weekend 2009