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New Mitre 10 store, Beachlands, Auckland, NZ

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Three large retaining walls were required to stabilise a steep bank on a construction site for a new Mitre 10.

Our solution

TTT SED Poles, H5 treated, 10.0m x 400mm SED, 166 pieces, were used for the retaining walls.

The poles were TTTested proof tested to prove their strength.

TTT SED Poles are naturally tapered, machine-peeled poles. Minimal wood is removed during processing so each pole retains its strength.

TTT Timber, H5 treated, 150x50mm, arrissed-edge SG8, was used for the retaining wall rails. The timber was machined to a constant width of 148mm so when installed the horizontal lines all matched. Jacks were also used to ensure the timber fit tightly against adjacent boards.

Wall 1 was 60m long up to 3.8m high.

Wall 2 was 94m long up to 4.8m high.


Project challenges

The site was a sloping section with an earth bund at the top of the slope.

In order to maximise the use of the site the retaining walls were placed right at the toe of the earth bund.

Retaining walls were required to stabilise the bund and protect the roadway situated above the bank, before the dig out could commence.

Construction needed to take place from the top down otherwise the bank would have collapsed.


The roadway was a main road and use of this road needed to remain unaffected.

The site was restricted for space.

Construction of the Mitre 10 was to take place at the same time.

Construction needed to take place during winter so installation needed to be rapidly completed before the weather deteriorated.

The ground conditions were silty clay and sand stone.

H5 treated Radiata Pine timber piles were determined as the best solution.

Wall 3 was 12.4m long up to 2.8m high.

Before excavation the TTT SED Poles were drilled into the sand stone and concreted in place.

The retaining walls were built from the top down, in 1.5m deep sections. After the poles were installed a section of wall was excavated, the poles exposed, and timber rails affixed with s/s washer head screws.

This method of installation meant the poles retained the bank while the wall was completed safely from the other side. There was no disturbance to the roadway above.

The retaining walls were completed in 3 weeks – well under the clients expected timeframe.

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