The Sandpit and the Pines: The rise and fall of a highway

Thursday, 19 October 2017

NCTIR site manager Julia Roberts explains the works at the Sandpit, near Clarence.

Road workers north of Kaikōura are tackling the most challenging sections of State Highway 1 as the Christmas deadline creeps closer. Reporter Jennifer Eder checks how the road is looking since the November earthquake tore the highway apart.

The Papatea Fault wreaked havoc on State Highway 1 in Clarence, 34 kilometres north of Kaikōura.

In one patch, the ruptured ground lifted the highway 4 metres into the air; in another the southbound lane ripped away from the centre line and plummeted 6m down the hillside.

It's a challenging repair job, hampered by spring rain and sea breezes, but North Canterbury Transport Infrastructure Recovery crews are cutting a swathe through the rural community to get the highway back in action.

Sand is visible under the old highway's asphalt, revealing why the area is called the Sandpit.

* Residents fret over road rumours as highway deadline approaches

* Quake shuts off Clarence Valley access, isolates farmers and residents**

The Sandpit

Before the quakes, the locals called the area just south of the Clarence Bridge 'the Sandpit', after the dark sand under the grass and between the pine trees.

Pulling the wire fence out of the concrete was the first job when crews arrived in March.

So it may have come as no surprise that during the quakes, the highway that passed over the Sandpit crumbled.

The highway split along the centre line and the southbound lane fell about 6m down the hill, revealing sand under the asphalt, several metres deep.

When the Sandpit is complete, 330 gabion baskets will line the wall holding up the southbound lane.

NCTIR project manager Kevin Lambe pokes a finger into the wall of sand beneath the old highway.

'The old highway was built on a hill, and on sand which doesn't hold very well.

NCTIR site manager for the Sandpit Julia Roberts reckons the road could be sealed in November.

'It was built years and years ago. But I would have done it differently.'

Site manager Julia Roberts says the 25-strong crew have gone through about 150 pairs of gloves since work at the Sandpit started in July.

Waipapa Limestone, by the Clarence River, supplies the limestone for the Sand Pit road.

'The store person thinks I'm collecting gloves because we go through so many pairs, just from moving the gabion rocks around.'

The uplifted area on State Highway 1, at the Pines.

The heavy, rough-edged gabion rocks must be placed in large wire cages, called gabion baskets, by hand, layer by layer, to form a new 6m wall of the highway so it can be resealed at its original height.

Crews must fill 20 baskets a day to finish their section of the highway on time.

Instead of resting on sand, the new southbound lane will be sealed over limestone chips.

Normal gravel is in short supply and concrete crushers in Clarence cannot pump the gravel out fast enough.

NCTIR project manager Zach Knutson at a culvert at the south end of the Pines.

So Waipapa Limestone, a quarry near the Clarence River, is producing limestone gravel to build up the southbound lane between the sand and the gabion wall.

Lambe reckons limestone is better than normal gravel for the hillside job.

The 4m lift was more noticeable in March, before crews cut a chunk through the middle for the highway.

'It's quite light and porous. That means water can pass through it easily, whereas gravel would hold any moisture and add weight to this side of the road.'

There are four other sections of the highway, north and south of Kaikōura, that have crumbled and need gabion basket edging, but the Sandpit is the largest section, with 330 baskets to be filled along 150m of highway.

Roberts says the wall will be finished and the road filled in about a month.

'Then we'll smooth the road over and get working on the pavement.'

Pine trees line the 4m wall of dirt that has been sliced through for the highway.

The Pines

South of the Sandpit is the Pines, where the Papatea Fault rupture lifted the highway - passing lane and all - by about 4m.

Workers have since excavated a road right through the middle, so the highway is bordered by 4m walls of dirt, topped with pine trees.

They then transported the dirt they removed to fill in other sections that slumped instead.

Project manager Zach Knutson estimates his trucks have shifted 170,000 cubic metres of material from the 1.6km of highway at the Pines.

That's about 10,000 truck-loads moved since March, he says.

Rock from the Clarence River, a stone's throw away, has been crushed to make gravel to fill the road.

'We try to use as many local subcontractors as we can,' Knutson says.

'We've been very lucky with the locals, they've been more than helpful with us. They all share our goal of getting the highway open as soon as possible.'

The road just needs one more layer of gravel and chip seal over the top, and should be finished next week, depending on the weather, Knutson reckons.

The weather must be fine when the top layer of chip seal is laid, or the quality of the surface will suffer.

'It's not ideal, working through winter,' Knutson says.

'It's always challenging, and you're always pushing yourself to get the next patch absolutely perfect. But I like a challenge.'

After the top layer of chip seal is laid, crews will turn their focus to the gutters and road edge, the finishing touches.