With major population growth in the greater Brisbane area, the 39 km Logan Motorway had exceeded its capacity. A major upgrade commenced in 2016 to widen sections, decrease congestion and construct new on- and off-ramps. The AU$512 million project aimed to improve safety, reduce travel times, enhance connectivity, and futureproof the road network. The project was fully financed and delivered by Transurban Queensland.
Golder delivered geotechnical services during design and construction for CPB Contractors, who managed the detailed design and construction of the project. A major challenge of the project was to provide cost-effective design solutions that would minimise traffic disturbance. We developed design solutions for the earthworks, ground treatments and cut and erosion treatments, as well as for the foundations of 17 bridges and other structures (e.g. gantries, noise walls and fauna crossings), and for 19 retaining walls of various types. We designed temporary works and stabilisation measures, ensuring safe construction and minimal disruption of the motorways. During construction, the Golder team provided supervision and support, including advice and geotechnical inspections.
A challenge we thrived on was designing a soil nail retaining wall formed by the near-vertical cut of an existing bridge spillthrough at the Logan-Gateway Interchange. Using 2D Finite Element Analysis (FEA), we identified significant induced forces in the bridge abutment piles, so we applied our 3D FEA skills to confirm that the new retaining wall would not jeopardise the integrity of the bridge piles. During construction, we continued to monitor the existing bridge abutments and retaining wall, confirming their satisfactory performance and eliminating the need to strengthen the bridge piles. This delivered cost savings and avoided traffic disturbance during construction.
Our geotechnical design solutions improved the constructability of this large project and maximised safe traffic flow. Our solutions avoided the need for piling near traffic, reduced earthworks, reduced construction time, minimised settlement, and improved stability and erosion protection of existing cut slopes for greater safety and reduced maintenance. We used existing shallow foundations where possible and used bored rather than driven piles to reduce noise and environmental impacts. By minimising cut along the Gateway Extension Motorway we achieved better sustainable outcomes for the environment and community.