GRAND CANAL QUAY WALL REFURBISHMENT

GRAND CANAL QUAY WALL REFURBISHMENT

Dublin docklands has seen a massive regeneration in the first part of the 21st century with the relocation of Dublin’s financial sector to modern office buildings along the banks of the River Liffey. The Historic now run down 206 year old Grand Canal dock is located on Dublin’s Southside,it joins the River Liffey with the Grand Canal and now stands surrounded by architect designed office and apartment blocks.

The docks quay consists of large granite sets unusually bed upon a random rubble wall, over the decades there has been a number of collapses and repairs to the six walls of the L shaped dock. A previously commissioned diving structural survey had highlighted a number of voids and defects which could result in a future structural failing that would cause considerable disruption and safety issues for the docks new high profile neighbors.

In the spring of 2007 Norfolk Marine were given the task of devising a method of both repairing and structurally reinforcing the ageing quay wall, with work commencing in early summer. The one hurdle being that no plant was to be based on the quay; instead all operations would have to be carried out from water based plant.

First the water level in the dock was lowered and the granite sets which are visible above the water line were re-pointed with lime mortar.Next the voids highlighted in the diving survey were either in repaired by Norfolk Marines diving stone masons using available masonry blocks or filled using concrete bag work.

The final operation was to reinforce 240 linear m of the structure below the waterline. To achieve this a specialist shutter 10m in length and 5m deep was designed and commissioned. The shutter utilized a weld mesh and removable fabric formwork face together with grout bag seals. Prior to placing the shutter it was necessary to drill and fix a pattern of stainless steel helical ties which would tie the new concrete face to the random rubble.

All the concrete used was a micro concrete mix containing fiber reinforcement and no aggregate larger than 7mm in diameter.

Fabric formwork is preferable for marine concrete repairs as the porous fabric allows the free water in the concrete mix to bleed down to a water cement ratio of 0.4. This gives a significant improvement in strength and durability over concrete placed in conventional shuttering. With design of concrete thickness and mix design incorporating GGBS and fiber reinforcement to enhance resistance against chloride/sea salts a long lifespan can be obtained. In the case of the Grand Canal project another benefit was the resulting blemish free finish once the fabric face was removed. Norfolk Marines staff achieved a shutter turnaround of 3 days equating to an area of 17m2 of quay being reinforced per day.