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EastLink Tunnel – Permanent Concrete Lining and Waterproofing Design

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Author K Assi, F Lebbing and E Taylor
ID P200803020

Description

The $2.5 billion EastLink project is a 39 km tollway and includes twin
three-lane, 1.5 km long, undrained driven tunnels with cross passages every 120
m. The hard rock tunnels are being built to avoid passing the motorway through
the Mullum Mullum Valley and help preserve the unique flora and fauna in the
area.


The design of the permanent concrete lining and waterproofing system for the
EastLink tunnels was both innovative and practical, to meet the demanding
environmental and production constraints of Australia’s largest road
project.


This paper describes several key aspects of the tunnel design and
construction, including:


  • design of fully tanked, permanent concrete tunnel linings for the main tunnels and cross passages to withstand 37
    m head of water pressure in combination with potential rock loading in the
    future;

  • optimisation of the tunnel shape to minimise the amount of
    reinforcement required and the design of special welded mesh which was developed
    within manufacturing constraints;

  • 100 year design life and durability considerations in every aspect and detail of the design including concrete mix
    design and stray current mitigation;

  • development of a precast invert solution
    for the main tunnel permanent concrete lining to enable faster lining
    construction and to minimise risks to the tunnel membrane associated with fixing
    reinforcement and construction traffic;

  • development of prefabricated reinforcement details for the junctions between the main tunnels and the cross
    passages to enable faster construction and minimise risks to the membrane
    associated with fixing reinforcement; and

  • incorporating the tunnel drainage sump
    at the lowest cross passage in the alignment, resulting in deep excavation to
    satisfy the required storage volumes for drainage.