Continuous earthquakes have left Christchurch with extremely diverse and variable ground conditions, including liquefaction of waterlogged sand and silts, a high water table and significant deposits of large cobble stones.
Harker Underground Construction General Manager Leigh Bishop said that these unique geological conditions mean that the installation of pipelines in either built-up areas or under railways and roads can be difficult.
“We have sourced a Taurus hammer supplied by TT Asia Pacific which is ideally suited to short trenchless installations, vertical or horizontal, through these displaceable soils. It is rather like an underground pneumatic torpedo exerting 18,500 Kn of force and driven by big mobile compressors,” said Bishop.
The hammer can ram pipe 600-2500 mm in diameter and individual casings 6-12 m long which are then welded together or pre-welded in lengths up to 80 m long and is currently at work for Fulton Hogan on tunnel crossings beneath Christchurch’s new Southern Motorway.Article continues below…
“One of the hammer’s key advantages is that by driving the pipe through Christchurch’s predominantly sandy-silty ground, prior to excavation, the risk of collapse is taken away. It is a very safe methodology in these conditions giving you structural support before you start digging.”
At the same time Harker is working closely with long-time partner Belcher Industries, from Pukekohe South of Auckland, to develop a new concept TBM that can cope with Christchurch’s silts, sands and cobbles.
“While the hammer thrusts steel pipe forward, a TBM machine works like a worm, eating a forward-path underground and simultaneously laying sections of concrete pipe behind it, a process called pipe jacking. The process means there is little disturbance to home and business owners above where the pipeline is being installed. It also avoids damage to environmentally sensitive areas and avoids tree roots from being damaged.
“To date we have not been able to not been able to source TBM technology, internationally, which can cost effectively cope with Christchurch’s varying ground conditions and lay pipelines accurately, but we are confidently working our way towards a ‘local’ solution with Bert Fourie and his team,” he said.
Since 1999 Mr Bert Fourie, Belcher’s owner, has grown his TBM manufacturing business (now called Fourie Tunnelling Systems), developing and manufacturing eight machines for the New Zealand market. Harker has used these machines to achieve some notable pipejacking milestones: undertaking one of the longest pipejacks in New Zealand (600 m of 2100 mm diameter pipe), installing New Zealand’s first curved pipejacked line; pipejacking the largest diameter pipe in New Zealand (3000 mm diameter) and installing pipes at 24 m below ground level.
Fourie is now recognised internationally as an innovative tunnelling machine designer, according to Harker.
“These machines work like a worm, eating a path forward underground and at the same time laying sections of concrete pipe behind it – a process called pipe jacking,” said Bert Fourie, Belcher Industries owner.
Further north, Harker pipe jacked a 380 m long tunnel 18 m under the Ellerslie Racecourse. The $A3.8m contract is part of Auckland Council’s sewerage and stormwater infrastructure upgrade. The project took six months to complete.