The Metro Tunnel is a key rail infrastructure project currently under construction in Melbourne, Australia that includes the construction of twin 9-km rail tunnels between South Kensington station and South Yarra with five new underground stations. While TBMs are being used to build most of the Metro Tunnel, station box excavation and tunnelling between the two CBD stations is being undertaken by roadheaders.
Site geology comprises interbedded Siltsone and Sandstone known as Melbourne Formation. The mineralogy in its unweathered state typically comprises a mineral assemblage principally of quartz (35% up to 59%).
The Cross Yarra Partnership, a consortium comprising of, John Holland Pty Ltd, Lendlease Engineering Pty Ltd and Bouygues Construction Pty Ltd, initially contracted Grydale to provide a ventilation design system for the project. Grydale were later contracted for all dust collection systems required for the project.
Initial engineering consultation converting the design from an Overlap or Cross-Over Extraction methodology to the now in-situ proven Full Extract methodology. The complete extract system is designed to remove all contaminants from the tunnel at the face and supplies fresh clean air for Civil and Mechanical and Engineering Works.
The design was created using Ventsim Design 5 to simulate ventilation, airflows, pressures, heat, gases, radon, fire and other key ventilation data to be considered along with managing the financial constraints of the project. The design was separated into 13 stages, representing the tunnel area changes with dust collectors for each stage, with additional axial fans to boost airflow in the latter stages of construction.
Melbourne Metro provided some unique challenges for the ventilation design: space and noise constraints plus the location within the CBD. The ventilation system was designed around the last dig sequence where maximum air flow is required. The ventilation design utilises scrubbers for each stage, with additional axial fans to boost airflow in the latter stages of construction.