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

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The Forrestfield Airport Link project in Perth used artificial ground freezing (AGF) to enable safe excavation of four cross passages beneath or near the operating airport. AGF was selected as an alternative to surface jet grouting, which was impractical because drilling rigs with tall masts could not be used in the restricted airport environment. A brine-based freezing system formed temporary, watertight and structurally stable frozen-soil walls, followed by sequential excavation and permanent lining.<br /><br />Design and construction faced high groundwater pressures, variable ground conditions, strict limits on airport-related ground movement, and severely constrained tunnel space. Freeze pipes had to be installed around the TBM’s steel support frame, ventilation ducting and slurry pipes, while avoiding joints in the tunnel lining. Detailed 3D planning, laboratory testing of frozen soils and finite-element analyses informed pipe layouts and freeze-wall requirements.<br /><br />Temperature sensors, tunnel convergence instruments and extensive surface, groundwater and structural monitoring tracked the freezing process and potential effects on airport infrastructure. A web-based system provided real-time data and automated alarms. During the first cross passage, monitoring showed that freezing near the tunnel lining was slower than expected. U-shaped copper pipes carrying brine were added to actively cool these contact zones; the measure was then used for the remaining passages. Fans and heaters also addressed condensation that complicated installation of the waterproofing membrane.<br /><br />The first three passages beneath the airport were completed successfully, and AGF was also adopted for a fourth passage on the project’s critical path after permeability tests indicated that the existing treatment did not meet requirements. COVID-19 travel restrictions prevented planned European expert attendance for the final passage, but remote reviews and additional reporting enabled its completion on schedule. The project demonstrates the value of careful design, monitoring and adaptable construction methods in complex underground works.

Keywords

Forrestfield Airport Link

artificial ground freezing

cross passages

Perth airport

groundwater pressure

frozen-soil walls

brine freezing system

tunnel excavation

monitoring system

permeability tests