Auckland
CASE STUDY
Manganui Gorge Suspension Bridge
One year since opening, we take a look back at one of our most challenging yet rewarding projects - designing robust foundations to support a 100m long footbridge near the summit of Mount Taranaki.
PROJECT OVERVIEW
Nestled amidst the rugged volcanic landscape of Mount Taranaki, New Zealand, the award-winning Manganui Gorge Suspension Bridge stands as a testament to Riley's contribution to awe-inspiring infrastructure. This 100-metre-long footbridge, creating a safe link across the previously treacherous lower gorge crossing, presented a unique set of challenges that demanded robust solutions and meticulous execution in a harsh alpine environment.
Riley's engineering team diligently applied their expertise to address the project's unique challenges:
Robust design solutions
Recognising the unpredictable nature of Mount Taranaki's volcanic rock, Riley's engineers devised a rock anchor and foundation strategy to suit the complex geological environment and needs of the bridge. This allowed contractors to install anchors using specialised heli-portable equipment, thoroughly test them to verify capacities, securing the bridge's foundations to ensure its long-term stability.
Riley has a long-standing partnership with DC Structures Studio, New Zealand’s leading specialist long-span footbridge design firm. The project team's mastery of advanced numerical analysis and design techniques ensured the bridge was not only structurally sound but also aesthetically pleasing, blending seamlessly with the natural beauty of the surroundings.
Adaptation to site conditions
Riley engineers demonstrated much-needed agility and responsiveness during construction by adapting their designs based on real-time feedback from drilling conditions. This ensured the design intent was maintained whilst balancing constructability and costs.
Understanding the client's needs, they applied their construction experience to inform adjustments to the anchor parameters and drilling strategy to accommodate the limitations of heli-portable drilling equipment, keeping the project on schedule and within budget.
Risk assessment and mitigation
Riley's engineers conducted comprehensive geotechnical analyses to evaluate potential hazards such as variable rock quality, seismic loads, and rockfall risks. This diligent approach ensures the bridge's structural integrity and longevity is securely anchored and supported in the face of natural forces.
They also provided the client with a clear understanding of the risks and benefits associated with different anchoring options, empowering them to make informed decisions that balanced cost and durability.
COLLABORATION: THE CORNERSTONE OF SUCCESS
Riley's success on the Manganui Gorge project was underpinned by their collaborative approach, working seamlessly with project partners:
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Over many years and successful projects, Riley has formed a strong partnership with DC Structures Studio, an award-winning bridge design firm led by architect and structural engineer Dan Crocker. This collaboration ensured the bridge's design was not only functional and safe but also an elegant addition to the landscape. Sustainability and integration of local iwi narratives were further cornerstones of the design
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The team's combined expertise in geotechnical engineering, advanced numerical analysis, and innovative architectural and structural design resulted in a bridge that is both structurally sound and visually captivating.
Department of Conservation (DOC):
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Riley maintained open and consistent communication with DOC staff throughout the project, ensuring all stakeholders were well-informed and involved in key decisions.
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They worked closely with DOC's in-house engineers and project managers, ensuring the solutions were practical, maintainable, and aligned with DOC's specific needs and constraints.
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Riley's flexibility in adapting to site conditions and incorporating contractor feedback was instrumental in keeping the project on track and within budget, demonstrating their commitment to client satisfaction.
Construction Partners:
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Riley's coordination with construction partners was exemplary, ensuring smooth execution of the project and prompt resolution of any issues that arose.
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Expert advice from in-house anchor specialists like Paul Aynsley, ensured the anchors were installed and tested to the highest standards, even in challenging alpine conditions.
CHALLENGES AND RESOLUTIONS
The Manganui Gorge project presented its share of challenges, but Riley's engineers, with their problem-solving mindset and collaborative approach, navigated them successfully:
Remote location:
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The bridge's remote alpine location posed logistical hurdles in transporting equipment and materials, a common challenge in many infrastructure projects.
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Use of heli-portable drilling rigs and other specialised abseil equipment allowed the project to overcome this obstacle, ensuring efficient construction despite access constraints.
Variable geological conditions:
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The unpredictable volcanic rock conditions at Mount Taranaki made drilling installation and foundation execution a complex task, requiring careful planning and ongoing on-site feedback.
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Riley engineers tackled this challenge by carefully inspecting prepared rock surfaces, coordinating production anchor testing, and analysing results to gain valuable insights into the ground conditions. This allowed them to refine the design for optimal accuracy and cost-efficiency.
Photos provided by DC Structures Studio
OUTCOMES AND ACHIEVEMENTS
The Manganui Gorge Suspension Bridge project stands as a testament to Riley's commitment to engineering excellence, achieving several significant outcomes:
Positive community impact
The bridge has been embraced by the community, DOC, and local iwi, with its design incorporating cultural elements that enhance its significance and acceptance.
Increased accessibility
The new bridge has significantly improved safety and accessibility for hikers, making the area more attractive to tourists and providing a boost to the local economy.
Sustainable construction
The project prioritised sustainability through efficient resource management and environmentally sensitive construction methods. The design achieves a 100-year design life, ensuring the bridge’s longevity for future generations.
DC Structures Studio received an Association of Consulting & Engineering (ACE) gold award for professional services in delivering the Manganui Gorge Suspension Bridge.
CONCLUSION
The award-winning Manganui Gorge Suspension Bridge project is a shining example of Riley's engineering expertise, collaborative approach, and dedication to client satisfaction. By combining clever design solutions, adaptability to site conditions, and thorough risk management, Riley helped deliver a project that not only met but exceeded the client's expectations. The project showcases Riley's ability to work effectively with project partners, including the bridge designer, client, and constructors, ensuring a successful outcome in a challenging and environmentally sensitive context.