Geohazard Engineering
AMETI Eastern Busway
Soil nail stabilisation of up to 11 m cut slopes for the Auckland Manukau Eastern Transport Initiative — design enhancements delivering cost savings while exceeding specification.
- Location
- Southeast Auckland
- Main Contractor
- AMETI Alliance
- Designer
- GSI NZ
- Timeline
- 2021
- Scope
- Soil nail and mesh stabilisation of two large cut slopes up to 11 m high
Design
Design Enhancements on a Competitive Tender
The Auckland Manukau Eastern Transport Initiative (AMETI) Eastern Busway is a major transport infrastructure project in Southeast Auckland, significantly improving transport options, reliability, and journey times across the region. The busway is constructed on the north side of Lagoon Drive, widening the road on the northern cliff side to avoid impacts on the adjacent basin.
As part of the widening, two large cut slopes up to 11 m high were created, requiring soil nailing and a slope stabilisation mesh facing. GeoStabilization NZ competitively tendered for the slope stabilisation package. During the preliminary design stage, our engineering team identified opportunities to enhance the conforming design — widening anchor spacing and shortening anchor lengths — without changing the design intent or overall solution, and without requiring changes to the building consent.
Build
Self-Drilling Anchors in Volcanic Tuff
The Lagoon Drive corridor has mixed volcanic tuff geology — welded and unwelded — presenting a risk of collapsing ground during drilling. GeoStabilization NZ proposed the use of a self-drilling, grout flush anchor system using low-carbon steel hollow bar. This product had been extensively used and scrutinised during the Kaikōura earthquake rebuild, where it was reviewed by the wider NCTIR engineering team including Beca and WSP.
The self-drilling system eliminated the need for casing in collapsing ground conditions, improving installation efficiency and programme. Combined with the anchor spacing and length enhancements, the approach delivered significant cost savings for the client while maintaining the structural performance required by the design specification.
Deliver
Cost Savings. High-Quality Outcome.
The AMETI Eastern Busway stabilisation works were delivered with a robust quality assurance programme exceeding the requirements of the conforming specification. Design enhancements resulted in meaningful cost savings for the client alongside a reduced construction duration. The self-drilling anchor system performed reliably in the mixed volcanic tuff conditions, avoiding the programme delays associated with collapsing ground in conventional drilling.
The completed slope stabilisation system provides permanent protection for the busway corridor and demonstrates GSI NZ's approach to competitive tendering — looking for engineering improvements that benefit clients rather than simply delivering the minimum conforming solution.
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