Cross River Rail

Cross River Rail is a 10.2km rail line between Dutton Park and Bowen Hills, which includes a 5.9km twin tunnel under the Brisbane River and Brisbane CBD. The project also includes construction of four new high-capacity underground stations at Boggo Road, Woolloongabba, Albert Street, Roma Street and redevelopment of the existing over Dutton Park Station.

Three adit tunnels linking the Roma Street Station Cavern to the Vertical Transport shaft were required to be located below and in close proximity to existing pile foundations of a bridge structure supporting the Inner Northern Busway (INB). The INB forms a critical component of Brisbane’s transport infrastructure and is required to remain operational throughout the duration of the Cross River Rail project. Undermining the INB pile foundations would require approximately 2.5m thick concrete adit linings and results in a Queensland Rail (QR) asset directly supporting a Department of Transport and Main Roads (DTMR) asset. The complexity of adit construction and administrative issues of supporting structures operated by different authorities leant itself to an alternate structural and geotechnical scheme.

ADG Engineers was engaged by CBGU JV to help develop a construction methodology to mitigate settlements on the INB bridge structure caused by tunnelling of the adits and design new permanent foundations for the existing bridge structure piers.

ADG Engineers in conjunction with EDG Consulting (Geotechnical) developed a staged partial demolition and construction of new foundations for the live INB bridge structure.

The works were staged to construct new micropile foundations and pilecaps, install temporary props and jack them against the INB deck, cut the piers from their existing pile foundations, and install a new steel collar that transfers the column superstructure forces into the new micropile foundations. The steel collar was designed to translate vertically using four 200 Tonne hydraulic jacks, nested in specially designed jacking pockets. This allowed the columns to be jacked to correct differential settlement between column pairs caused by the tunnelling works approximately 15 meters below.

A detailed study of the INB bridge was performed to calculate the maximum permitted vertical displacements between neighbouring columns, termed ‘trigger levels’ used to quantify levels of damage associated with various magnitudes of differential vertical settlement.

This complicated scope of works required significant consultation with the Cross River Rail Joint Venture, Delivery Authority (Queensland Government) and The Department of Transport and Main Roads.

The combination of the temporary works engineering, permanent structural design, development of a staged construction methodology and collaboration with various Queensland Government organisations, the Cross River Joint Venture and geotechnical engineers resulted in the continued operation of the INB during tunnelling works.