Artificial Ground Freezing: A Smart Application Below the Airport of Perth-PPT Presentation

PPT Presentation

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The Perth Airport rail project will provide a new metro connection to Perth’s eastern suburbs, including 8.5 km of new track and 7.14 km of twin tunnels. Because restricted airport access made jet grouting impractical at selected cross-passages, artificial ground freezing (AGF) was used to stabilize the ground during excavation.<br /><br />Four cross-passages were constructed using AGF. Design was informed by subsurface investigations and laboratory testing of frozen, unfrozen and thawed soils. Engineers planned the freeze-pipe layout around tunnel geometry and areas where drilling could damage the segmental lining. The design specified a 1.5 m frozen-soil thickness between the -2°C isotherms, an average temperature of -10°C, and a maximum permitted airport ground heave of 1.5 cm.<br /><br />Freeze pipes were drilled into the soil, and chillers circulated refrigerated brine through the system. Temperature sensors tracked freeze-wall development and performance during excavation. Extensive airport and tunnel monitoring also measured ground movement, groundwater levels and pressures, tunnel convergence and strain, vibration, and other impacts. Data were shared in real time through a web-based system with automated alerts.<br /><br />Monitoring identified two areas where excavation could reduce the ice-wall thickness. An additional active cooling system was installed, enabling excavation to proceed in compliance with design requirements. The project also demonstrated a strong relationship between freezing activity and surface ground movements.<br /><br />Despite technical challenges and COVID-19 travel restrictions, the team completed all four cross-passages safely and on schedule. Three were in a sensitive area beneath Perth Airport, while the fourth was on the project’s critical path.

Keywords

Perth Airport rail project

artificial ground freezing

cross-passages

twin tunnels

freeze pipes

ground stabilization

subsurface investigations

temperature monitoring

ground heave

tunnel excavation