Ground Engineering
Wimbledon Road — DSM Landslide Repair
126 deep soil mixing columns — cost-effective alternative to traditional piling for a road-threatening landslide.
- Location
- Wimbledon Road, 35 km SE of Waipukurau
- Client
- Central Hawke's Bay District Council
- Main Contractor
- GSI
- Timeline
- 2024
- Scope
- 126 DSM 800 mm columns, counterfort drains
Design
A Smarter Alternative to Traditional Piling
Wimbledon Road, 35 kilometres south-east of Waipukurau in Central Hawke's Bay, had experienced ongoing movement for several years, progressively damaging this integral transport route. Central Hawke's Bay District Council required a permanent solution without the cost and disruption of traditional concrete piling.
GSI collaborated with Stantec and CHBDC to design a deep soil mixing (DSM) solution — 126 DSM columns at 800 mm diameter and 8 m depth, arranged in a triple-row shear key to intercept the failure plane. DSM offered significant cost advantages over conventional piling while achieving the required shear resistance. The design incorporated 3 m deep counterfort drains to manage groundwater pressures driving the slope movement, and also included pavement reconstruction and an upgraded stormwater infrastructure with a new concrete swale drain.
Build
126 Columns, In-Situ Mixing, Minimal Disruption
GSI self-performed all works as main contractor, installing 126 DSM columns across the landslide footprint. The DSM process involves little or no spoil generation — the binder is mixed into the existing soil rather than displacing it — which simplified waste management on the rural site and allowed drilling spoil to be reused on-site, minimising costs and environmental impact.
Counterfort drains at 3 m depth were installed to intercept groundwater, reducing pore water pressures driving the movement. Works were completed with minimal traffic disruption — the road was kept open throughout the construction period under a traffic management plan. Pavement reconstruction and the new concrete swale drain were also completed as part of the programme.
Deliver
Wimbledon Road Secured — On Time, Within Budget
The project was completed on time and within budget, with no incidents. GSI also optimised the DSM scope during construction — providing the client with significant cost savings while maintaining full structural performance. Central Hawke's Bay District Council received a permanent solution that addresses both the failure mechanism and the underlying groundwater driver.
Wimbledon Road has become a reference project for DSM applied to rural road landslide repair in New Zealand — demonstrating that the technique delivers cost-effective, low-disruption solutions in the district council context, where budget constraints are often the most significant barrier to permanent repair.
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Related
Problem
Slope Instability →Related Projects
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