Solving a tight problem

Lower North Island rail movements have taken on a whole new versatility with the completion of the Kai Iwi tunnel bypass.   HUGH DE LACY reports.

KaiIwi_4.jpgIt was probably just a coincidence that in 1887, the same year that the railway line from Wellington to New Plymouth was completed, Chinese-born entrepreneur Chew Chong opened the Eltham dairy factory that became the foundation of Taranaki’s core primary industry.

It would be another 30 years before the Main Trunk Line from Wellington to Auckland saw its first traffic, but by then Taranaki was already supplying Wellington and Britain with dairy produce. Today Chew Chong’s foresight is embodied in the giant co-operative dairy company Fonterra, and the railway has become even more important to dairy farmers than it was in his day.

Until this year though, Fonterra was restricted in both the speed and the volume of milk that it could transport from its sprawling inventory of farmer-suppliers in the lower North Island to its monster factory at Whareroa in South Taranaki. The bottleneck on the New Plymouth line occurred at a brick-lined 208 metre tunnel at Kai Iwi, nine kilometres northwest of Wanganui, that had been built in 1879.

So tight were the approaches to the tunnel, and so small was the tunnel itself – four metres in diameter – that freight trains had to slow to 10kph to negotiate it, and only the small 2.6 metre containers could be squeezed through it. That all changed in June of last year when a 992 metre long bypass was opened about 150 metres away from the old tunnel.

KaiIwi_1.jpgNow, with the completion of the Kai Iwi bypass and the day-lighting of three other tunnels at the eastern end of the Manawatu Gorge (see Contractor, October 2008), all the main lines in the North Island rail network, including the branch lines from Marton to New Plymouth in the west and Napier in the east are capable of carrying the 2.9 metre high-cube containers that are making rail more competitive with road transport. This east-west rail corridor has the potential to rival the North Island Main Trunk in economic importance.

The Kai Iwi and Manawatu Gorge projects are part of the National Rail Strategy to 2015, which prioritises regional development with a particular eye, in Taranaki’s case, to the dairy industry. Commissioned by rail network owner OnTrack, the Kai Iwi deviation cost $5 million and involved the moving of 455,000 cubic metres of dirt to make a 300 metre long cut with walls 45 metres high. One wall is benched to assist in drainage, while the other is a batter slope.

The headline contractor was New Plymouth company Hurlstone Earthmoving, with most of the work being done by its recently-acquired subsidiary, Wanganui-based Hayes Earthmoving Services, and with John Hayes himself at the helm.

KaiIwi_3.jpgThe Kai Iwi deviation’s design represented four years’ work for the Wellington office of employee-owned Tonkin & Taylor which, with Robin Scott as project manager and Richard Justice as senior engineering geologist, included helping with the consultation with the farmer who owned the land the deviation passed through, as well as obtaining the planning consents from the Horizons Regional Council.

The deviation comprised a large cut through a ridge bordering the Mowhanau Stream, with the ground being mostly soft sand and gravel layers over wet mudstone, necessitating some complex drainage design. Much of the spoil from the fill was used to create the railway embankment, whose toe was hard up against the stream in places.

The cut itself began with a couple of scrapers feeding 30 tonne Moxy dump trucks, and at peak involved 10 trucks, three bulldozers and five excavators. One of the excavators, a 30 tonne Caterpillar, was fitted with a GPS system that not only allowed Tonkin & Taylor to monitor the design as the work progressed, but considerably speeded up the work and minimised the potential to over-excavate.

KaiIwi_5.jpgThe rail embankment involved 3100 cubic metres of Geogrid earth reinforcement, 500 metres of sub-soil and buttress drains, 100 metres of 600-750 millimetre concrete culvert construction and a 22 metre long bridge. The bridge, whose abutments required soil nails and shot-creting, was a Class One pre-stressed double-T construction that saved $25,000 by replacing the originally planned steel bridge.

Apart from the earthworks, Hurlstone was also contracted by OnTrack to remove the tracks from the old line, including those in the tunnel, and to help OnTrack staff to build and commission the 1000 metres of new track. Hurlstone also worked alongside OnTrack staff to lay the 1600 concrete sleepers that formed the new track. Construction started in January 2007 year and took 22 weeks to commissioning, though some minor supplementary work continued.

No sooner was the new deviation commissioned than the first train went through with 10 of the high-cube wagons among its load.  

KiwiRail’s Palmerston North manager, Brian Fryer, says the project has already stimulated greater movement of goods by rail along the New Plymouth line.

KaiIwi_2.jpg“New Plymouth traffic is increasing dramatically and high-cubes are becoming more popular.  The Kai Iwi deviation means we can take those high-cubes used, for example, by Fonterra’s Whareroa plant. We can also re-position empties to and from Port Taranaki, and if there is a track problem on the Main Trunk, we have a back-up option of moving railfreight between Auckland and Wellington via Taranaki.”

Tonkin & Taylor’s Richard Justice says the on-time-and-budget completion of the job vindicated the efforts put in at the consultation and planning stages, including the negotiations with the landowner to ensure the design fitted in with his management of the surrounding sheep and beef farm.

By the time Chew Chong died in 1920, the New Plymouth-Wellington line had ensured the survival of the Taranaki dairy industry he had pioneered, even though the Stratford-Okahukura line that connected New Plymouth to the Main Trunk and Auckland was not completed until 1933.

Today the old Kai Iwi tunnel that linked New Plymouth with Wanganui and the Main Trunk at Marton sits in isolated splendour, devoid of rails and with gates at either end blocking access. Given the significance of the Kai Iwi deviation to Taranaki industry, it might just be a fitting monument to Chew Chong. 

Contractor Vol.33  No.1  February 2009
All articles on this website are copyright to Contrafed Publishing Co. Ltd.