Constructing a 27-kilometre motorway through fractured rock in one of New Zealand’s most seismically active regions was always going to demand more than standard ground engineering solutions. Transmission Gully motorway, built across steep saddles and deep gullies north of Wellington, was at the time Australasia’s largest greenfield infrastructure project. Its scale, geology, and exposure to extreme weather made it one of the most technically demanding slope stabilisation programs ever attempted in New Zealand.
Complex Geology and Difficult Access
The new four-lane alignment was cut across multiple active fault zones, with rock that bore the scars of past seismic events. Conditions could vary from hole to hole - some drilling faced solid rock, while others collapsed as soon as they were advanced. Frequent dewatering was needed to stabilise the faces, and every storm brought renewed access challenges. On such terrain, progress could only be maintained with disciplined safety systems and the ability to slope stabilisation techniques in real time.
Geovert’s Role
Geovert was awarded the major slope stabilisation by the CPBHEB Joint Venture, with a three-year program of works. Our scope required not just technical capability, but the ability to scale operations quickly to support the wider earthworks schedule. To achieve this, we established a dedicated compound onsite, complete with a covered workshop, 40-foot office, spare parts and tooling. This ensured production continuity, even when ground conditions demanded rapid changes in methodology.
Our core team of over thirty geotechnical specialists delivered the works, supported at times by night shifts to match the pace of excavation. The fleet included seven drilling rigs, two robotic-nozzle shotcrete pumps, and two high-reach all-terrain EWPs. Rope access drilling crews were deployed on the steepest faces to install temporary supports and carry out work in otherwise inaccessible locations.
Technical Delivery
Across the programme, Geovert installed tens of thousands of rock bolts and soil nails, many with inclined drains drilled up to 50 metres into the fractured rock. Over 25,000 square metres of shotcrete was applied to cut slopes, combined with the installation of active Geobrugg mesh systems to provide long-term surface stability. Benching, bolting, and shotcrete were applied dynamically, adjusted continually in response to variable ground behaviour.
Safety and Culture
Safety was never compromised. Transmission Gully tested crews with constant exposure to weather, rockfall hazards, and high-risk access, yet Geovert maintained an exceptional safety culture that was acknowledged across the project team. Our people worked under strict systems, but with the flexibility to manage hazards as they emerged.
Equally important was the culture within the team. Geovert’s own cultural framework emphasises collaboration and care for our people, and this was evident throughout the program. The dedication and commitment of the crews, not only to the technical delivery but to each other’s safety, was central to the project’s success.
Outcome
Through a combination of technical expertise, operational resilience, and a collaborative approach, Geovert successfully stabilised the slopes that enabled Transmission Gully’s construction. The works supported the accelerated delivery of one of New Zealand’s most significant infrastructure investments, providing a resilient transport corridor that will serve the region for generations.
Transmission Gully remains a benchmark project for ground engineering in Australasia - an example of delivering safely and at scale in some of the toughest conditions imaginable.
For a closer look at the works and conditions on site, watch the full project video below.