With perhaps the exception of a bailey bridge, it is not often the demolition and re-build of a bridge is completed within three days. Richard Silcock explains.
Wairoa based Quality Roading and Services (QRS) demolished and rebuilt the Waitahora Bridge within 72 hours despite a severe storm mid-construction and the urgent task of getting a pregnant woman over the Waitahora Stream to the nearby maternity hospital during the process.
The wooden, 90-year old, 12-metre long, one-lane bridge over the Waitahora Stream near Frasertown on the former SH36 (the inland route between Wairoa to Gisborne) was in urgent need of an upgrade, widening and strengthening to cater for heavy trucks (HPMVs) and the increasing amount of road traffic.
As the alternative route added considerably to travel times, the Wairoa District Council (WDC) required the work to be completed within a 68-hour timeframe.
Mike Wilson, QRS construction manager says they made local history in dismantling the old bridge and constructing a wider and stronger replacement bridge within the time requested by the council.
“In accepting the contract we undertook to complete the project safely and efficiently within the specified timeframe.
“By meticulous pre-planning and dedication by all those involved in the rebuild, including our sub-contractors, that’s exactly what we did.”
For Mike, having previously been an engineer in the NZ Army and having worked on a number or projects in often remote areas of the Pacific Islands, the logistics of getting the project done were fairly straightforward, however, as he puts it: “There were some fairly distinct complexities to consider.”
The bridge had been modified some years before, however this project called for a complete overhaul and replacement of the upper structure.
“In the six weeks prior to the bridge rebuild commencing we did a lot of preparatory work, including consultation with the design engineers (WSP Opus), communication with the local community on the bridge closure, traffic management planning and strengthening work around the sloping terrain and stream bank.
“Detailed planning and additional work was also required to ensure they could operate safely and meet the environmental requirements.
“This included silt runoff protection of the waterway, erecting scaffolding for the work teams and support platforms for the machinery.
“As the stream was prone to flooding we also temporally diverted it and secured and protected the bank by constructing reno mattresses and gabion baskets, which were installed without contaminating the waterway.
“Due to the design specification and site location, materials for the bridge rebuild itself had to be ordered and procured well in advance of the construction starting, with, in some cases, up to three-month delivery to site delays.
“We also had contingencies in place for almost every scenario and this proved to be most beneficial when it was found the 30-tonne mobile crane could not handle the deck and attached beams all in one lift; and when we had to transport a woman in an advance stage of labour across the old bridge just prior to demolition commencing.”
Mike says they started on the actual demolition and rebuild at 9am on a Friday in May last year and were due to have it completed by 5am the following Monday.
“To ensure we achieved this we had two shifts working, with a smaller team working throughout the night under diesel-generated power floodlights.”
Following closure of the bridge, the old deck and the beams were lifted separately from the abutments by the crane and removed by truck from the site. The bridge frame was then cleaned down using sandblasters and repainted. The new prefabricated steel beams, supplied by Universal Engineering (Gisborne), were then lifted into position and welded and bolted in place.
“We then built and secured the new spiking timber and baulk deck, before the running deck, kerb and guard rails were installed.
“Where the galvanised brackets and coach bolts hold the timber baulks to the spiking timber we had to recess the bolt heads before we could put the running planks down.
“This was a bit of a mission and took quite a bit of time, as all the holes for the bolts had to be drilled from beneath. We had to be spot on with the alignment and make sure the high powered drill-bit did not hit someone working on the deck above.
“By Sunday evening we had completed most of the deck and railings, constructed the bridge approaches and re-instated the curbing.
“Our greatest challenge however was the weather which really turned to custard on the second day with the rain becoming torrential overnight.
“We had lifted the original bridge deck on the Friday and all was progressing well until the rain storm struck.
“We then had to contend not only with the driving rain but also the sheer volume of water in the rapidly rising stream.
“Having to watch the water level, ensure the safety of the team and keep the night lights working in the driving rain and wind certainly added to the drama.”
Despite the pressure of getting the project completed within the timeframe in the adverse weather, QRS carried out regular checks throughout the rebuild to ensure the bridge met specification, was progressing on schedule and was within the contracted budget.
“Due to a high degree of skill, leadership, determination and perseverance our teams pushed through in some very tough conditions and got the job done on time,” says Mike.
“It is a credit to them.”
In addition to the Waitahora Bridge rebuild, QRS strengthened the Deep Creek Bridge further up the road and recently secured a number of contracts totalling $29 million for work around the East Coast and Hawke’s Bay regions, which include a road maintenance contract for WDC, flood repair work and a $10.8 million contract awarded by NZTA for safety improvements to roads in the area.
One of the QRS excavator operators, Tui Paikea, also won this year’s CCNZ Hawke’s Bay/East Coast Regional Excavator of the Year Award.