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Sydney Metro Northwest - Castle Hill Cavern

Project data

Location: Sydney, Australia

The $8.3billion North West Rail Link project is the longest transport tunnelling project in Australia’s history and is expected to be complete by 2019. The 15 km long twin tunnels are being constructed to connect Sydney’s northwest suburbs to the city for the very first time.


The Cross-Over Cavern at Castle Hill is 20.5 m wide and 159 m long, with the cavern opening up to the eastern side of the station box, consisting of two different cross-sections:

  • A lower cross section 14m high and 131m long
  • A higher cross section 17.5 m high over 25 m long, with a 2.5 m long transition section between these two cross-sections

The cavern terminates with a headwall where it connects to two smaller bored tunnels.

The 500 mm thick cavern lining is reinforced up to the construction joint above the lower wall, at the widest part of the cavern.

The walls and crown lining above this level are unreinforced.

The between 800 mm and 1200 mm thick headwall is completely reinforced


Thiess John Holland Dragados JV

Customer's benefit

  • Quick setup, and moving of the entire assembly using the Variokit traveller.
  • Fast pouring rate
  • High surface quality
Will Freeland
Project Manager

The assistance provided by PERI in coordinating the design requirements, the methodology and subcontractor suggestions, was integral to the success of the project.
When assembled onsite the mechanical nature of the form removed many manual handling and work at height risks, whilst the drive units allowed the unit to be propelled in a safe and timely manner, allowing further safety and program improvements.

PERI solution

  • PERI SB single sided brace frames and special Wall formwork for the lower cavern walls, above the invert.
  • PERI VARIOKIT formwork for the upper crown lining in the standard and enlarged cavern sections.
  • The combination of PERI SB, TRIO, VARIOKIT and Rosett systems for the headwall.
  • Specially fabricated components for the entire system.
  • The PERI UP Rosett Flex system for providing access to various areas of the formwork
  • The tunnel formwork measures a staggering 20m in width with heights varying between 14m and 17m
  • Using VARIOKIT traveller to move the massive 140 tonne tunnel formwork system