Dr. Helen Chow’s, an Associate Geotechnical Engineer and Patrick Wong’s Senior Consultant co-authored paper contributes to advancing the understanding of soil stabilisation and foundation support in sensitive ecological zones.
Their paper – “Ground Improvement over Soft Clay for the Main Access Road to and from Port Macquarie Airport”, was recently shared to delegates at the 5th International Conference on Transportation Geotechnics (ICTG2024) in Sydney Australia.
The site’s challenging geotechnical conditions, including deep soft clay deposits, high groundwater levels, and the environmental constraints imposed by adjacent wetlands, required a nuanced, high-performance solution to accommodate future traffic demands. Tetra Tech Coffey’s innovative application of rigid inclusions with a geogrid reinforced gravel load transfer platform not only ensured structural stability but also minimised environmental impact, offering a sustainable, economically viable design tailored to a sensitive ecological zone.
Challenges addressed
The project aimed to upgrade Boundary Street to a twin-carriageway that could withstand predicted traffic growth while addressing several key challenges:
- Geotechnical Complexity: The project site is underlying with paleochannel with depth of soft clay in excess of 8m depth, which posed risks for settlement and required careful design to ensure stability.
- Environmental Sensitivity: Boundary Street runs adjacent to protected wetlands, necessitating a construction approach that minimized ecological impact, especially for the habitat of local fauna.
- Flood Resilience: Frequent flooding in the area required the upgraded road to provide flood immunity for events up to a 1-in-20-year return period without affecting surrounding ecosystems.
- Construction Constraints: Limited space and high groundwater levels presented further challenges for deploying standard ground improvement techniques, demanding creative engineering solutions to fit within the narrow corridor and avoid prolonged impacts on nearby wetlands.
Design Options Considered
The Boundary Street upgrade project aimed to address severe geotechnical and environmental challenges while supporting increased traffic demand to and from Port Macquarie Airport. Several design options were evaluated before selecting the final approach:
Three primary solutions were evaluated: structural bridging (expensive), preloading with wick drains (time-consuming), and rigid inclusions with a load transfer platform (cost-effective and environmentally friendly). Tetra Tech Coffey’s approach enabled an innovative design that met the council’s budget, minimised ecological impact, and ensured resilience and longevity for future traffic demands.
- Given the site’s proximity to sensitive wetlands and local fauna habitats, Tetra Tech Coffey’s solution-focused design minimised the environmental footprint while ensuring structural integrity and flood resilience.
- Working closely with project stakeholders, including environmental and civil engineering teams, Tetra Tech Coffey ensured that the final design met the council’s objectives for resilience, sustainability, and future-proofing the infrastructure to support anticipated growth in airport traffic.
Driving sustainable solutions for major infrastructure
The selected ground improvement solution combined rigid inclusions with a geogrid reinforced gravel load transfer platform, designed to support the road embankment and limit differential settlement . This approach achieved several outcomes:
- Enhanced Stability: The use of rigid inclusions improved soil stability, significantly reducing long-term settlement and ensuring consistent road performance over the years.
- Environmental Conservation: The solution minimized environmental impact by maintaining a confined construction footprint and protecting adjacent wetland ecosystems.
- Cost-Effectiveness and Efficiency: Compared to other solutions like structural bridging, this design proved more cost-effective and faster to implement, aligning with project budgets and timelines.
- Sustainable Engineering Practice: The adoption of low-strength concrete and reinforced load transfer platform offered a more sustainable approach, balancing structural demands and environmental impact.
Tetra Tech Coffey’s ground improvement solution for the Boundary Street upgrade addressed the multifaceted challenges of the project by integrating geotechnical innovation with environmental stewardship. The use of rigid inclusions and a load transfer platform offered a balanced, sustainable, and cost-effective approach that met the council’s requirements for resilience and future-proofing. This solution minimised environmental impact, preserved local ecosystems, and ensured the infrastructure would support anticipated growth in airport traffic.
Helen and Patrick’s work underscores the role of sustainable design in advancing transportation geotechnics.
For more information in relation to this technical paper, contact the authors:
Dr. Helen Chow | Associate Geotechnical Engineer, Tetra Tech Coffey, Sydney Australia at [email protected]
Patrick Wong | Senior Consultant, Tetra Tech Coffey, Sydney Australia [email protected]
Acknowledgments
The authors are grateful to PMHC and Hopkins for this successful project, their kind permission to publish this paper and their review comments.
About the event
ICTG2024 served as a pivotal gathering, drawing together experts dedicated to advancing sustainable, technology-driven solutions for urban transport infrastructure. The event highlighted the global challenges of transportation infrastructure and underscored the innovative paths forward in geotechnical engineering. Visit the event website 5th ICTG (2024) | 20-22 November 2024