Project Description

The Cross River Rail (CRR) North and South Portals mark critical entry points for the project’s twin tunnels. Constructed using a ‘cut and cover’ methodology, these portals were engineered to meet both structural and operational demands. The process involved installing piles to create a rectangular framework, which was capped with concrete slabs. Once the framework was in place, excavation was performed, followed by the installation of precast prestressed beams to seal the structure and form the roof. These 'cut and cover' structures now serve as the vital entrances for trains accessing CRR’s underground system, supporting the efficient flow of rail services through the network.

Project Challenges

Northern Tunnel Portal The Northern area of the CRR project focuses on constructing the northern tunnel portal, situated within the existing rail corridor at Normanby, between the newly built underground Roma Street station and the upgraded Exhibition station. This portal will serve as the entry and exit point for trains at the northern terminus of the twin tunnels. The Northern Tunnel Portal spans approximately 400 metres, consisting of a 60-metre cut and cover section, a 35-metre propped piled wall section, a 120-metre cantilever piled wall section and an 85-metre in-situ open trough section. Site establishment activities commenced in January 2021, which included installing CRR site offices and facilities, erecting fencing around the portal site, and piling works to facilitate excavation. The Northern Portal structure is flanked by existing rail lines which remained live throughout construction and lies beneath a proposed new rail line. The structure was designed such that this infrastructure was not adversely impacted throughout construction.

Southern Tunnel Portal The southern segment of the project, spanning between Park Road, Dutton Park, and Buranda stations, encompasses the construction of the southern tunnel entrance and the reconfiguration of existing rail infrastructure to seamlessly integrate CRR into the South East Queensland rail network. This section is particularly intricate, as it intersects with a complex network of commuter rail lines and a freight line. Additionally, the presence of the Eastern Busway and various other services and utilities adds to its complexity, making it one of the most significant technical challenges in the project’s design. Spanning approximately 380 metres, the southern tunnel portal form changes along its length to suit the earth retention and Tunnel and Ventilation Systems (TVS) requirements. Beginning at the Southern end of the portal, the structure is a pure cantilevered retention wall, due to TVS requirements, the open trough transitions to a cut and cover tunnel. The southern portal interfaces with four existing rail tracks and their associated support structures, including the freight flyover. We developed an engineering solution to modify the support conditions of this existing bridge, underpinning it with new reinforced concrete bored piles and twin beam. Preliminary site preparation activities began in early October 2020, including the installation of CRR site offices and facilities, the erection of fencing around the portal site, and piling works to support the excavation. Four existing rail lines run through the southern portal, which were to remain active throughout most of the portal construction. The design and staging of the southern area were carefully planned to accommodate the existing rail network.