Geotechnical Access Innovation: The Waikato River Bridge Soil Nails Project
When Hamilton's new Waikato River Bridge required slope stabilisation on a sheer 30-metre embankment above New Zealand's longest river, Geovert developed the country's first crane-suspended drilling platform for geotechnical construction.
When conventional methods meet extraordinary challenges, innovation becomes necessity. The Waikato River Bridge Soil Nails project in Hamilton demonstrated how creative engineering solutions can transform complex geotechnical challenges into opportunities for industry advancement, earning recognition at the 2022 CCNZ National Awards.
The Challenge
The project involved stabilising a 1,400m² slope extending 60 metres along a sheer 30-metre embankment above the Waikato River for Hamilton City Council's new transport network. The site presented multiple complexities: variable volcanic ignimbrite geology known for its unpredictable conditions, proximity to New Zealand's culturally significant Waikato River, and access constraints that would typically require conventional wagon drill methods with rope access.
The geological conditions were particularly challenging. Walton group volcanic ignimbrites are deposited rapidly under extreme conditions, creating materials with common voids, high porosity, and variable density that can change dramatically within metres. This variability makes anchor bond capacity difficult to predict and increases the risk of grout loss during installation.
Rethinking the Approach
Rather than accepting the conventional wagon drill methodology expected at tender stage, Geovert's engineering team identified significant disadvantages with this approach. Wagon drills would limit hole diameter to 100mm, require complete vegetation removal for equipment movement, create substantial environmental risks through air flushing, and necessitate 50% longer anchor lengths to achieve required load capacities.
The solution emerged through collaboration with mechanical engineering specialists - Motovated. A custom-designed drilling platform capable of supporting a crawler drill rig, suspended from a 180-tonne crawler crane positioned at the slope crest. The platform was engineered to accommodate both the drilling equipment and crew while enabling precise positioning across the work area.
Engineering Innovation in Practice
The custom platform represented a New Zealand first in geotechnical construction and an expansion on Geovert previous smaller crane basket designs. Designed to accommodate both a crawler drill rig and a two-person crew, the platform provided stability and safety while enabling the crane to position the drilling operation across a 40-metre radius. This configuration tripled productivity compared to conventional methods while dramatically reducing safety risks for operators.
Key design considerations included maintaining platform stability under drilling forces, ensuring crew safety with appropriate guard rails and fall protection, and compliance with NZ Code of Practice for Cranes Part 17. The platform underwent rigorous third-party certification before deployment, with final load testing completed on-site.
The team maintained multiple drilling methods on-site to adapt to varying geological conditions. The approach proved effective in managing the challenging volcanic materials while maintaining drilling efficiency.
Environmental Protection Through Design
Protecting the Waikato River from construction debris presented an equally complex challenge. With no flat ground available for conventional silt fencing, the team developed an innovative horizontal silt fence system featuring a cantilevered timber platform constructed on anchors drilled into the slope at 1.5-metre centres.
The platform, built from 20mm plywood with 100x50 timber runners and covered with filter cloth, captured drilling spoil and debris while allowing water drainage through designed perforations. This system enabled continuous visual monitoring and regular maintenance, ensuring no pollution entered the river. The effectiveness of this solution was validated when the principal contractor requested it remain in place for subsequent bridge construction activities.
Industry Implications
The crane-suspended platform methodology offers potential applications for similar projects where conventional access methods present unacceptable safety or environmental risks.
The innovative silt fence design provides a replicable solution for protecting waterways during construction activities on steep terrain, though specific implementation details require careful engineering for each application. The project's environmental management approach, balancing construction requirements with ecological preservation, offers a framework for similar culturally and environmentally sensitive projects.
Perhaps most significantly, the project demonstrates how questioning conventional methodologies can lead to superior outcomes. By challenging the expected wagon drill approach, the team developed solutions that were simultaneously safer, more efficient, more environmentally responsible, and more cost-effective.
Technical Specifications Summary
Slope area: 1,400m² by 60m length
Slope height: 30 metres above Waikato River
Anchors installed: 640 soil nails at 8.3m length
Total drilling: Over 5,100 metres
Platform capacity: Custom-engineered for drill rig plus crew
Crane capacity: 180-tonne crawler crane
Working radius: 40 metres maximum
Safety outcome: Zero harm throughout project duration
Environmental outcome: No pollution incidents