Bridges

The $400 million Tonkin Gap and Associated Works Project is part of an infrastructure package announced in 2019, addressing a major bottleneck on Tonkin Highway between the recent Gateway WA and Northlink WA projects and preparing the existing Northlink WA corridor for the construction of the Morley Ellenbrook rail line. The Project was awarded to the Tonkin Gap Alliance in late 2020 with construction completion due in late 2022. The Tonkin Gap Alliance comprises Georgiou Group, BMD, WA Limestone, GHD and BG&E working with Main Roads WA and PTA to deliver the project.

The Project includes a total of nine new beam bridges, one launched bridge, two underpasses, one underpass extension, three footbridges, two rail dive structures and a number of noise and retaining walls. In addition, the Project required modifications to all existing bridges and structures along the route to meet current standards regarding load and barrier capacity and rail collision requirements.

The Project constraints, including a constrained site footprint, geotechnical and groundwater challenges and the requirement to maintain traffic flows through the busy corridor required some innovative approaches to meet the requirements in an economic and constructable manner. This included overlapping or abutting new and existing structures, optimised construction methodologies including integral and launched bridges, underpinning existing structures, strengthening of existing barriers and modifications to meet rail collision requirements.

The paper will provide an overview of the Project including alternative approaches developed during the tender phase and innovative design approaches required to meet the Project requirements. The paper is focused on key aspects of the Project not covered by other papers proposed for the conference including optimising the project footprint, modifications and strengthening of existing structures and coordination of design with construction methodologies to meet constraints.