The equipment was supplied to building and civil engineering contractor L&M Keating for a project to lower the level of the Lough Atalia Road – one of the busiest roads in Galway – as it passes beneath the main Irish Rail tracks.
The Lough Atalia Bridge is a low, 19th century cast iron arch structure, and until now, height restrictions have meant that any vehicles over 3.68m high had to move towards the centre of the road to pass under it. However, it is not unknown for vehicles to strike or get stuck under the bridge.
The City Council’s solution was to lower the road by 1.3m, and L&M Keating undertook the work during an eight week closure of the road during April and May 2015.
“As a result of the road level being dropped, storm water now has to be pumped away, so the contract included construction of a storm water holding tank and pumping station” comments the L&M Keating project manager. “A 45m long, 3.5m wide, 2.5m high tank was constructed using precast concrete culvert units, and sits below the road on the south side of the bridge, with the invert at a depth of 6m below road level” he added.
Groundforce designed and supplied a shoring system to retain the ground while the culvert sections were installed. As programme was of key importance, it was decided to create a watertight cofferdam around the entire area, consisting of sheets and frames to give large clearances between the cross struts and allow the culverts to be lowered into place without obstruction.
This system was made up of a combination of 6m and 7m interlocking GFI trench sheets installed using a MS4 piling hammer, supported by a Mega Brace waling beam and HSK80 cross struts.
Groundforce supplied the excavation support system for a period of 3 weeks while L&M Keating installed 19 precast concrete culvert units, each weighing between 12t and 14t, as well as a pumping chamber to house the pumps required to divert storm water over a length of 730m.
“This was complex excavation due to its size, tidal water conditions and varying ground conditions” comments Groundforce technical representative, Joe Lenihan. “The support system was originally designed using large trench box systems but due to the presence of water and the size of culvert sections, it was decided that the cofferdam system would be preferable to aid the installation sequence” he added. Groundforce has also supplied equipment for other elements of the project, including standard and lightweight trench box systems, Vertishore - lightweight shoring for between services - and pressure testing equipment for the new 400mm water main, over the course of the 8 week project.
L&M Keating, senior engineer comments: “We had a tight programme of 8 weeks to carry out this project. An array of existing services including water, gas and electricity were encountered within the job site, with these having to be kept live at all times. Despite this, the project was carried out in a timely manner with the roadway opened 3 days ahead of schedule”.