Ground Freezing with Liquid Nitrogen for TBM Cutterhead Maintenance - NAT2024

For the REM (Réseau Express Métropolitain) project, a 2500 m tunnel was built using a tunnel boring machine (TBM) under the Montreal Pierre Elliott Trudeau Airport (ADM). Although the geology under the Montreal Airport (ADM) would have been suitable for an excavation with a hard rock machine, the 􀂿rst section re􀁔uired an earth pressure balance (EPB) TBM due to the soft soil located under wetlands. After excavating 280 m, the TBM was blocked in a transition zone of unconsolidated, water-bearing soils directly above the underlying bedrock. A free air intervention was not possible due to these geological conditions. After several failed attempts to create a slurry cake for hyperbaric interventions, a ground freezing system was designed and implemented, incorporating angled pipes drilled from outside the wetlands to directly in front of the cutterhead. This paper discusses the engineering re􀁔uired to form a frozen, water-tight zone in front of the cutterhead using li􀁔uid nitrogen. It also describes the complex method of replacing the disc cutters while holding the ground freezing system active in a manner protecting the health and safety of the workers.