Design of the underwood road ventilation facility on WestConnex 1B Sydney

The WestConnex M4 East Project (Stage 1b) includes two new three-lane carriageway tunnels connecting the M4 Motorway near Homebush Bay to the City West Link and Parramatta Road in Haberfield. The Underwood Road Ventilation Facility (URVF) is located at the western end of the project siting directly above the westbound carriageway and alongside the existing M4 eastbound carriageway. The ventilation structure is 23.8 metres by 15.8 metres in plan and 40 metres high and compromises of six internal shafts. Five of the shafts support fans, damper and attenuator equipment ranging from 15 tonnes to 55 tonnes. The remaining shaft provides access into the mechanical shafts. The URVF is located directly above the westbound carriageway on the Homebush Bay Drive cut and cover structure. Due to construction program and highly congested construction area accommodating for large civil works, a precast structure was designed. The URVF structure comprises of over 16 levels precast wall elements, weighing approximately 13 tonnes each, and a series of internal precast floor with reinforced topping slabs tied to the precast walls. The vertical and lateral loadings are transferred into the underlying cut and cover structure via a series of 2.5-metre deep by 1.5-metre wide reinforced concrete beams with up to nine layers of reinforcement. In the structural design of the URVF, a sensivity analysis was undertaken to assess the impact of the cut and cover structure under due to wind and earthquake loading. In addition, impacts of modelling the precast joints to simplify the precast dowel connections was also assessed. As with the rest of the cut and cover structure, the URVF has been designed for a two-hour hydrocarbon fire which is not currently addressed in Australian design codes. Hence this posed challenges in the concrete mix design, reinforcement detailing and fire protection of the wall dowel joints.