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Concrete In Australia : September 2008
PROJECTS FREIGHT TRAINS TRANS-ADELAIDE METROPOLITAN PASSENGER TRAINS ACCESS PATH at-grade road and rail corridors. The underpass comprises two traffi c lanes in each direction, on-road bike lanes and a 3.2m-wide shared path on the southern side. At-grade works included access roads on the western side, providing partial connection between Glover Avenue and James Congdon Drive. The standard gauge freight line, owned by ARTC, was also re-aligned, resulting in a superior track alignment with almost zero disruption to the critical freight network. 1800 DEEP SUPER-TEE BEAMS 1350 BOREDPILES Figure 2. Cross section of the rail bridge superstructure. • maintaining safe pedestrian and cyclist movements around the site – particularly for two large schools – one of which was immediately adjacent to the site • minimising impacts on Park Lands at one end of the site • minimising impacts on heritage buildings either side of Henley Beach Road. • minimising amenity impacts for the adjacent residential communities. Early contractor involvement An interesting aspect of this project is the procurement method. Early contractor involvement, or ECI, is a very common form of delivery in the UK for medium sized infrastructure projects. Under this arrangement, the principal, builder and designer work collaboratively from the concept stage, with the minimum of constraints being imposed. A hard money contract is not signed until the design has been well advanced (in Bakewell’s case, to 80%). It is considered that this process enables all parties to better defi ne risk and encourages innovation. Many of the pitfalls of the design and construct type contract are thus avoided. DTEI decided to procure the Bakewell Underpass as the fi rst ECI project in South Australia and one of the fi rst in the country. From the designers’ perspective at least, this method has proven to be highly successful. The interaction of all relevant parties meant that constraints were fully understood by all. The progressive input from the project estimator ensured that effort was not wasted in pursuing cost prohibitive ideas. However, the focus on value, as opposed to lowest cost, allowed outcomes that would not necessarily have been achieved under a D&C model. General arrangement The fi nished structure shown in Figure 1 carries the busy east-west commuter road Glover Avenue under the north-south 50 Concrete in Australia Vol 34 No 3 Figure 3. Rail bridge precast headstock in position. DIAPHRAGM HEADSTOCK Rail bridge superstructure The cross-section consists of sixteen 1800mm-deep super-tee beams nominally 2m-wide – the fi rst time super-tees of this depth have been used in South Australia. The deck caters for six railway tracks (refer to Figure 2) – four broad gauge lines for suburban TransAdelaide trains, one standard gauge line shared by ARTC and Great Southern Rail and allowance for an additional standard gauge line to be installed at sometime in the future. In addition, an access path is provided along the eastern edge of the deck to allow passage for pedestrians and council maintenance vehicles across the underpass. An unusual and key feature of the design is the 2.1m-deep by 1.2m-wide diaphragm cast onto the end of the beams. This diaphragm supports the beams through shear friction, and provides the level surface required in order for the deck to be laterally launched into position. Transversely, the vertical bearings are located centrally over the piles, except for the bearings at each end. The diaphragm provided the necessary horizontal stiffness required for the launching operation.