McConnell Dowell Corp. Ltd. recently completed the Pringle Hill Pipejack, which forms part of the construction work on the Northern Pipeline Interconnector project being undertaken by the Northern Network Alliance (NNA) in South East Queensland, Australia.
The NNA consists of LinkWater Projects, McConnell Dowell, Abigroup and KBR.
Nearly 1,032 meters (3,405 feet) in length, the 2,100 mm (84 inches) ID pipejack is believed to be the longest yet completed in the Southern Hemisphere. This unique installation includes a significant vertical curve contributing to a 60-meter (198-foot) climb from the tunnel launch position to the final target destination.
The pipejack technique was chosen with a state-of-the-art guidance system to control the navigation around the curves and the necessary elevation change over the course of the drive.
A Herrenknecht AVND-2000AB microtunneling system was used to jack through the drive using the 3 meters (10 foot) long, 2,100 mm (84 inches) internal diameter reinforced concrete pipes that would form the final installed tunnel. During the course of the installation, 10 interjack stations were deployed throughout the pipe string alignment to keep jacking forces within the necessary limits of the jacking pipe through the curves and alignment changes and the designed capacity of the launch shaft.
All services and products used for the navigational control system were provided by tunnel navigation systems specialist, VMT GmbH, with the unit used on the Pringle Hill installation being supplied through the company’s Australian subsidiary, VMT Tunnel Guidance Pty, which is based in Brisbane.
The VMT SLS-Microtunneling LT (Laser Total Station) guidance system was chosen because, according to VMT, it offers significant advantages for longer or curved tunneling projects. The ability to determine, continually update and display the tunnel boring machine’s (TBM) current position, independent of drift or refraction, guarantees optimum control in long pipeline excavations and in complex curves.
The pipe jacking section of the tunneling works was completed on Nov. 1 2010, some five weeks ahead of program. Breakthrough was achieved to a very high accuracy with the drive being less than 50 mm (2 inches) off the target point in both horizontal and vertical planes.