INB Underpinning – Cross River Rail

As part of the Cross River Rail (CRR) project in Brisbane, a new underground station structure is required at Roma Street. The station structure will be located immediately adjacent to an elevated busway bridge forming part of the existing Inner Northern Busway (INB).

To cater for the driving of three adits for the Cross River Rail project beneath the existing Inner Northern Busway, an alternative foundation solution was required to support the structure, as the proposed adits clashed with the existing INB foundations.

Underpinning of the existing structure using groups of micropiles was adopted and EDG analysed the full construction sequence including the excavation of the adjacent shaft and adits to design the micropiles.
The underpinning solution adopted comprised micropile groups drilled around each underpinned pile connected with pile caps and loads transferred to the INB busway bridge columns via steel collars. Jacking systems were also incorporated to allow mitigation of structure settlements.
Modelling included both pile response and finite element to assess the ultimate and serviceability cases and predict settlement of the piles and structure under working loads due to all construction activities.

Construction Phase Services involved logging of the micropiles and review of movement data during transfer of load from the piles to the micropiles, and the subsequent adit tunnelling operations.

Reviewed by DJC 8/6/23

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