Geohazard Engineering
Clevedon Kawakawa Road
Eight landslip sites repaired across Clevedon Kawakawa Road following subtropical rainstorm events — design/build delivery under emergency timeframe.
- Location
- Clevedon Kawakawa Road, Auckland
- Main Contractor
- Broadspectrum
- Designer
- GSI NZ
- Timeline
- Emergency response — post subtropical rainstorm events
- Scope
- Eight underslip sites — soil nails, shotcrete, GCS retaining walls
Design
Eight Sites. One Design/Build Contract.
Following a series of subtropical rainstorm events, Kawakawa Bay and the wider Auckland region suffered extensive landslip damage. Many roads developed both underslips and overslips, with some requiring full closure. Broadspectrum contacted GeoStabilization NZ through their longstanding relationship to provide a competitive design/build solution for multiple underslip sites on Clevedon Kawakawa Road.
GSI NZ successfully negotiated a design/build package for eight slip sites across the road. Working under an emergency timeframe, our in-house engineers carried out site investigations and mapping alongside the available geotechnical information to develop repair solutions that minimised cost through innovation and experience — GSI NZ has remediated many hundreds of similar underslip failures across New Zealand's regional road network.
To provide rapid turnaround, a number of engineering assumptions were made during the design stage and subsequently confirmed using sacrificial soil nails tested to failure — a practical approach that allowed construction to begin before full geotechnical investigation was complete.
Build
Innovation at Two Adjacent Sites
The eight repair sites involved a range of solutions depending on the specific failure geometry and road reinstatement requirement at each location. Two adjacent sites in close proximity illustrated the range of approaches available within a single design/build contract.
One site was repaired with a straightforward soil nail and shotcrete solution — no shoulder build-out was required, and the road formation could be reinstated directly over the stabilised face. The adjacent site involved a more complex repair: soil nails combined with a Geosynthetically Confined Soil (GCS) retaining wall to re-establish the road width that had been compromised by the landslide. The GCS system is a significantly lower-cost alternative to conventional mass concrete or precast retaining walls, and this design/build solution delivered savings to the client of approximately 20% over traditional retaining methods.
Deliver
Eight Sites Repaired. Road Restored.
All eight underslip sites on Clevedon Kawakawa Road were repaired under the design/build contract, restoring full road access following the subtropical rainstorm events that caused widespread landslip damage across the Kawakawa Bay and Auckland region.
The programme was delivered under an emergency timeframe, with in-house engineering, investigation, and construction managed simultaneously. Broadspectrum's decision to engage GSI NZ through their existing relationship rather than running a formal tender process allowed works to begin within days of the initial callout — a critical factor in minimising the period of restricted access on a route used by the local community.
The project is representative of GSI NZ's regional road underslip repair capability — from the rapid assessment and emergency design approach to the use of GCS retaining walls as a low-cost alternative to conventional structures. The 20% cost saving delivered on the GCS wall site demonstrates the value of design/build delivery, where the engineering team's familiarity with the available solutions allows cost-effective alternatives to be identified and implemented without the delays of a separate design process.
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