Rail project speeds ahead on fast track

Ontrack says it is surprised at how quickly work has progressed on the New Lynn project. Photo / Greg Bowker

Reinforcing steel is outlining a platform inside the $160 million New Lynn railway trench, after diggers spent less than a month reaching their baseline level, 8m below surrounding streets.

KiwiRail subsidiary Ontrack says construction of a central platform to divide future duplicate railway tracks has already begun as the diggers continue to scoop the rest of an 800m trench through the heart of New Lynn.

Ontrack project director Ted Calvert said yesterday that about 40m of the trench had taken shape between long, pre-sunk retaining walls, at the site of a new railway station to be built between road bridges at the Clark St roundabout and Hetana Ave.

A concrete slab 800m thick has been laid along about 12m of the trench, enabling steel workers to start building a 200m platform, which will be large enough for trains of at least eight carriages once the project is completed next winter.

Mr Calvert admitted some surprise at how quickly contractor Fletcher Building's diggers had reached base level.

"We were doing a few trial digs and I went out just to see what the clay looked like and they were already down to the bottom," he said.

"We have had quite a bit of rain and I really thought it might knock us around."

But he said enough pumps had been available to enable a fleet of excavators to dig their way down with little fuss, using a combination of long-arm machines and "baby diggers" used to lift clay up to intermediate benches in relay operations.

The trench is being built between two long "diaphragm" retaining walls, sunk into the ground in 6m sections, a technique Mr Calvert said had never before been used on such a scale in New Zealand.

He said he believed that the expertise Fletcher was gathering in using the technique would have helped a consortium it is leading to win a $340 million construction contract announced by the Transport Agency this week for the $430 million Victoria Park motorway tunnel project.

The motorway tunnel will be built as a 440m covered trench, making it just over half as big as the New Lynn railway cut, which will vary from 22m in width at the station to 12m towards the Portage Rd end.

Ontrack will build road bridges to replace New Lynn's existing railway crossings at Clark St and Veronica St, leaving Waitakere City Council to pay - with Transport Agency subsidies - for two new crossings at Hetana St and Memorial Drive, in support of an upgraded town centre and bus interchange.

Fletcher Building infrastructure chief Mark Binns said the method being used for the railway trench could be adopted for the Victoria Park tunnel, which he has promised to try to complete in time for the 2011 Rugby World Cup.

But he said it was still being weighed up against other techniques.

"It is certainly one option. We have built up significant expertise in that area."