Whirokino Trestle and Manawatu River Bridge replacement

3 MinutesBy NZ Trucking magazineSeptember 26, 2017

Work is well underway to replace two existing bridges on SH1 between Levin and Foxton. The replacements will enable more efficient heavy freight movements on SH1, improve safety, and provide a better environment for cycling. The existing bridges are Class 1 and 50MAX capable, but HPMV need to travel via Shannon, a 14km detour.

Constructed in 1938, the existing Whirokino Trestle Bridge is a 1.1km-long, reinforced concrete bridge over the Moutoa Floodway and adjacent floodplain. It is narrow, nearing the end of its life, and not strong enough to carry some heavy vehicles. It requires ongoing maintenance to keep it functioning to full capacity.

The existing Manawatu River Bridge is a 180m-long, structural steel bridge over the Manawatu River, constructed in 1942. Like the Whirokino Trestle Bridge it is narrow, but also at risk from liquefaction in an earthquake.

At present there is no shoulder for cyclists on the existing bridges. The existing walking and cycling track on the floodplain will be retained, and the new bridges will provide a 1.2m-wide shoulder for cyclists.

Investigations identified a preferred option for the replacement of both bridges on an alignment immediately to the west of the existing SH1. The project cost is estimated to be $70 million and the works will take between two and three years to complete.

A temporary staging bridge has been constructed to provide access across the Manawatu River. The staging bridge is designed to carry the weight of the 100 tonne crane that‘s needed for construction, as well as concrete trucks and those carrying sand, fill and other materials. This allows materials to be transported onto the site without affecting SH1 road users. The staging bridge will be removed once the new bridges are completed.

A site access point has been created on the northern side of the trestle, allowing construction traffic access to the flood plain. This involved widening the shoulder on the left hand side (heading towards Foxton). Temporary traffic management will be in place while this access point is being used with a 70km/h speed restriction for approximately 300 metres.

Ground improvements in the form of concrete lattices are being installed. They are built with interlocking groups of piles that together form a framework that looks a bit like a beehive. These lattices strengthen the ground, keep sand and silt in place and help stop liquefaction in the event of an earthquake.

Concrete lattices will improve the ground for the northern and southern abutments of the new Manawatu River Bridge, and on the south abutment of the new Whirokino Trestle. Each abutment concrete lattice takes about four weeks to complete.

The aerial photo shows the Manawatu River Bridge and the temporary staging bridge, while the other photo shows the northern end of the Whirokino Trestle.