Tight site and a tight frame

For Fulton Hogan, tasked with constructing a new section of road, installing stormwater pipes and upgrading the sewer on a narrow site near Queenstown Airport, it was a race against the onset of winter and the tourist season. Richard Silcock explains.

Since opening in late December last year, the Eastern Access (Hawthorne Road extension off SH6) on the outskirts of Queenstown has reduced bottle-necks and travel times for travellers heading to the Remarkables Ski field or further south to Kingston.

Due to increasing traffic volumes and resulting congestion on SH6 and Kawarau Road, especially during peak tourist seasons, the Queenstown Lakes District Council contracted Fulton Hogan and engineering design consultants Stantec (formerly MWH) to design and construct an alternative 2.5 kilometre road to the north-east of Queenstown Airport.

Faced with a critical 15-month construction period they came up with a number of innovative solutions to minimise cost and deliver the project within the timeframe.

The opportunity was also taken to install stormwater infrastructure, street lighting and carry out landscaping. When it was found a section of the existing, nine year-old sewer was in need of replacement, the contract was expanded to include this as well.

The road construction entailed earthworks, the laying of stabilised sub-base and basecourse, and a 700mm deep fill-layer over a 1000-metre section of the alignment. The road was asphalt paved and the footpaths, kerb and channelling constructed of concrete.

While the contract specified tactile studs be used on the footpaths, which would have required several thousand holes to be drilled, the contractor suggested that tactile pads be used instead as these could be attached to the concrete using a two-pot epoxy resin.

“This not only saved a significant amount of labour time, but has provided a far better long term solution as it will require far less maintenance,” says Fulton Hogan’s project manager, Richard Lee.

“Another time/cost saving solution was our ‘automatic’ kerb leveller. We fabricated a levelling box which was attached to a grader blade when we were levelling out the kerb base prior to laying the concrete kerb itself,” says Richard. “This allowed us to utilise our GPS control system on the grader to achieve more accurate horizontal levels.

“It also reduced aggregate wastage, manual labour and saved a heck of a lot of time,” he says.

The stormwater pipe installation required a seven-metre deep benched trench to be excavated and the laying of 1800mm diameter PE pipe, one kilometre of which was across the Frankton Flats, while another section was from the top of the runway end safety area (RESA) embankment and involved installing over 200-metres of pipe over five-metres deep on the 45-degree slope.

“It was decided not to bench the embankment trench as this could have disrupted the existing stabilised material and required excavations of up to 11-metres wide to achieve the required bench depth,” says Richard. “Instead, and by excavating a trench width of only two-metres at the base, just the upper part of the embankment required benching.

Welding a seam in a stormwater PE pipe.

“The PE pipe was joined using EF sockets as this eliminated the need for our guys to enter the trench to bolt and tighten flange joints in the usual manner,” says Richard. “The pipes were placed and inserted into the socket of the previously laid pipe with the weld connections exposed along the top which enabled easier access for our welding team.

“Due to the trench depth we elected to backfill using pourable concrete at 17- 20MPa. This was poured to provide a flat surface which we then covered with compacted topsoil. This was done using a digger mounted plate compactor, eliminating the risk for our guys having to work on a steep slope with a 400kg compactor.”

It was during the excavations for the stormwater pipe that it was noticed that a section of the existing sewer pipe was showing signs of degradation and needed to be replaced.

“As this is the only sewer line running between the town and the nearby treatment ponds we only had a ‘shutdown window’ of 45 minutes to replace it, otherwise the sewage could have backed up and overflowed,” says Richard. “To overcome this we constructed a bypass pipeline to divert the waste while we welded in a new 800mm section of pipe.

“While this delayed the stormwater work by three weeks we managed to make up some time as the project progressed, however, with the addition of the sewer work this did add a further three months to the project overall.”

Richard says the project was made difficult because of a number of factors.

The airport remained open throughout construction with aircraft approaching to land on the adjacent runway.

“Due to the proximity of the runway and safety embankment, the nearby sewage ponds and the Shotover River, the work site was narrow making access for equipment and material difficult at certain stages of the works,” he says. “This was particularly evident when several crews were working at various different sections of the project and when deep trenching was being carried out.

“With the trenching taking up pretty much the width of the road, access for trucks and diggers was blocked, so we had to plan accordingly and instituted daily planning/logistical meetings with each crew supervisor so that everyone was aware of each other’s needs and timing.

“We were also working to an extremely tight schedule with only 15 months to complete the work, with some parts of the project such as the road needing to be completed and open before Christmas and the influx of summer holiday makers.”

Due to the proximity of the runway a management plan was compiled to identify and address potential risks/hazards which could have affected the safe operation of aircraft.

“This included keeping stockpiles of aggregate well away from the flight path and airport boundary, and revegetating areas as soon possible to minimise dust,” says Richard. “Machinery height restrictions were also put in place to comply with civil aviation regulations where we were working directly in line with the runway.”

Such was the innovation shown by the contractor while carrying out the project, it won the Central Otago CCNZ/Hynds construction award for projects over $5 million this year.

This article was first published in the September 2018 issue of Contractor Magazine.

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