Abstract
The Eastern Distributor Tunnels - the first major road tunnel project in Australia - are the preferred solution to traffic congestion problems, when compared with alternatives, in this inner urban environment. This is because of the reduced impact on residential housing, the improvement of the existing environment, less restrictions on future developments, and a reduction in noise and pollution. Developments leading to a tunnelled solution, traffic needs and reasons for route location are discussed. Criteria for design of tunnel alignments and geometry are described, including the restraints imposed by surface connections on profiles and grades resulting in low rock cover at tunnel portals. The main geotechnical restraints are a major weathered dyke at the shallow large span underground fork and the weathered Ashfield Shale capping the Hawkesbury Sandstone at a portal. Rock cuttability and excavation methods are discussed. Roadheader machines are the most suitable for the varying shallow arched cross sections required and the tunnel lengths involved but the use of blasting in special situations cannot be ruled out. Initial support for the major tunnel lengths will be provided by rock reinforcement in conjunction with shotcrete. Steel ribs are proposed in areas of low cover and weak ground. Final support will comprise an insitu concrete lining. Construction concepts and special tunnelling methods required at the shallow underground forks and tunnels are described. Discussion on tunnel drainage and waterproofing concludes that grouting and the installation of a dripshed where necessary will provide the essential requirements. The criteria for tunnel wall finishes and the various alternatives are presented. The tunnel ventilation system comprises a series of jet fans with one ventilation station per tunnel that discharges the polluted air via a shaft. Air quality studies at ventilation stations show that concentrations of pollutants will be significantly lower than that existing, due to the reduction in street level traffic volumes. The requirements for tunnel lighting, ventilation and emergency services are discussed and the systems are described.
Published Version
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