SH23 Whatawhata to Raglan slip repairs

17 April 2023

Contractors hard at work on building the retaining wall

Road to Raglan restoration nearing completion

The project to restore State Highway 23 between Raglan and Whatawhata, which was damanged by a serious underslip in February, is nearing the finish line.

Waka Kotahi NZ Transport Agency and its contractor are this week putting the finishing touches on the geosynthetic reinforced retaining wall, which has concrete piles drilled 12m deep into the hillside to support it.

The next stages are resurfacing the road and installing guardrails, and finally lane markings are needed to complete the project. Pavement sealing needs dry weather, so the actual timing of these last stages will very much depend on how much rain falls over the next few weeks. 

If the weather plays ball, it is anticipated the original highway will reopen by the middle of May.

A temporary diversion road was opened on 4 March to skirt the underslip that had closed the highway; this allowed geotechnical experts to thoroughly investigate the site, and for the best remedy to be decided.

Waka Kotahi is grateful for the generous co-operation of the landowners, which enabled work to begin on the temporary diversion road within days of the initial underslip.

Once the original highway is re-opened, the project crew will work on restoring the affected properties, including fencing, planting and landscaping.

The section of State Highway 23, known as the Raglan Deviation, began to crack in late January, when the ground was saturated following unprecedented rainfall. The cracks soon turned into an underslip, which significantly worsened after Cyclone Gabrielle, with a 30m long section of highway dropping around 2.5m.

For more information about how the geosynthetic wall is being constructed to stablise the hillside, check out this short video with Bruce Waugh, Principal Project Manager.

The mahi is hard, but look at the views!

The geosynthetic retaining wall is built layer by layer

For more details, background and photos, please go the project website