Three major highway projects in a row are under construction around the western side of Christchurch. HUGH DE LACY takes a look at the northernmost of them, the Western Belfast Bypass project.
FOR MONTHS CHRISTCHURCH traffic north of the city has been subjected to Auckland-style rush-hour delays, but a $112 million project – $90 million for the physical works – is on its way to fixing those snarl-ups by early 2018.
The Western Belfast Bypass project being built by Fulton Hogan will eventually halve the 42,000 vehicle movements a day that presently cause congestion all the way from the northern motorway’s Waimakariri River bridge, along Main North Road and into the city.
The essence of the Western Belfast project is to take southbound through-traffic around to the west of the city’s northernmost suburb, and hook it up with Johns Road which runs north-south between the city and its international airport.
The NZ Transport Agency project, with the two allied projects to its immediate south, is turning Johns Road into a bypass artery at a total cost of $322 million.
The five kilometre Western Belfast Bypass between the Groynes and the Northern Motorway connects the motorway’s four lanes with Johns Road just south of the Groynes recreational area, where a separate project is upgrading Johns Road’s two lanes to four, with a median barrier in between.
Further south still, where Johns Road becomes Russley Road, the four-laning is continuing through to the southernmost suburb of Hornby and SH1, and will feature an overbridge at Memorial Avenue which connects the airport with the city.
Other projects in the $900 million upgrade of the city’s main arteries include the Northern Arterial, which will go from the northern motorway to QEII Park where it connects to the artery to Lyttelton Tunnel, and the Southern Motorway that will connect Rolleston to Brougham Street to complete the eastern artery to Lyttelton.
The Western Belfast Bypass is being built on boggy flood-plain that has required no less than 650,000 cubic metres of bulk-fill to be brought in from local quarries and rivers.
The work started in May last year and was helped by a dry winter, followed by a protracted drought in the region.
“We were fortunate because once we’d stripped the topsoil we were able to get that initial half-metre layer of gravel down very quickly, and keep moving,” says Fulton Hogan project manager Ben Hayward.
Complicating the geo-tech programme, designed by Opus International Consultants, was the need to surcharge the three bridge locations, the southernmost over Groynes Drive, a second over Dickeys Road, and the northernmost over what will become the new northbound on-ramp.
“At all three of these locations we’ve filled through the bridge areas, built them up three metres higher than the final bridge height, and left them to settle and consolidate,” Ben says.
At the Groynes bridge site, which was always expected to have the biggest level of consolidation, the gravel embankment has settled more than 1.2 metres in six months, and at the northern on-ramp bridge the rate has been 700mm over the same time period.
“There was a lot of design work at the start, and that’s proving to be remarkably accurate,” Ben says.
A key factor in the geotechnical design has been the laying of no less than 150,000m2 of basal reinforcing geo-fabric – a tough fabric that looks and feels like the stuff they make seat-belts out of – along the length of the new western artery.
“When we’d stripped the topsoil, the basal reinforcing was laid and we then built the embankments over the top of it.
“The reinforcing layer ensured the large fill sites settled uniformly.”
It’s the first time Ben has seen basal geo-fabric used in such large quantities in the South Island, though it was a common ingredient of the SH1 upgrades north of Hamilton which passed over even boggier terrain.
The volumes of traffic, no less than the intricacies of three projects progressing concurrently, will pose some special challenges in traffic management as they near completion, and the new motorway works have to be tied into the existing network.
“We need to move the existing traffic onto a portion of our new motorway so we can construct the off-ramp which lies directly over the existing Northern Motorway, so early next year we will be diverting northbound traffic onto the new on-ramp in a temporary state so that the remaining roadworks can be constructed safely,” Ben says.
“The current Northern Motorway traffic flows will be maintained so we’re not going to disrupt that traffic: they’ll just be heading on a slightly different alignment so that we can build the rest of the motorway,” Hayward says.
Work started in May this year on the first of the three bridges of the Western Belfast Bypass, the seismic ground improvements and settlements having been completed.
The settlement period did not upset Fulton Hogan’s timeframe for the project, as it was always predicted by the designers and there was plenty of work to do before construction needed to start on the bridges.
“The geo-tech engineers had factored in the construction programme and it’s working very close to what was estimated, so it hasn’t had a major effect on the bridge construction rate,” Hayward says.
On its completion, the bypass will not only relieve congestion on Main North Road, but also allow further development in Belfast, something that could not be contemplated while traffic was at gridlock levels.
Along with a start to construction of the bridges and on-ramps, the Western Belfast Bypass stormwater swales and drainage piping is currently well under way, while road paving will be followed by landscaping, the installation of road safety barriers, traffic signs, road-marking and street lighting.
Ben says the work is being carried on with an eye to the progress of the two projects to the south, and it looks likely that all three will be completed about the same time, bringing a dramatic reduction in Main North Road traffic volumes, and the diversion of both north and south through-traffic – especially trucks – away from the suburb.