Open Face & TBM Tunneling
Once considered a niche technology and primarily used for mine shaft sinking, ground freezing is nowadays widely accepted as a versatile tool for the resolution of a range of subsurface challenges, particularly those related to both soft ground and hard rock excavation and tunneling.
Ground freezing offers several advantages unique to the construction of vertical shafts. The freeze can be implemented perfectly through the soil/rock interface, often the most difficult geology in which to create a groundwater cut-off by other methods. Proper instrumentation can provide assurance of the integrity of the full depth freeze prior to excavation.
Vertical and horizontal arches
Ground freezing can be utilized to ensure stability of sequentially excavated (SEM) or hand-mined tunnels. The freeze pipes may be installed from the surface, either vertically or battered, or they may be installed horizontally from access shafts to create a frozen envelope parallel to the tunnel alignment.
Cross passages and connector tunnels
Ground freezing can be utilized to facilitate connections between structures such as a cross passage between twin tunnels or a mined connection between deep structures. The frozen ground will conform to adjoining subsurface installations or obstructions, if necessary, to provide a composite cut-off structure.
Mixed face conditions
Mixed face conditions for a hard rock tunnel boring machine (TBM) can be alleviated by creating a frozen mass that encompasses the tunnel face, presenting a homogenous, strengthened zone to allow tunneling to proceed safely.
Mass ground freezing of a designated area along the tunnel alignment allows for a ‘safe haven’ for the tunnel boring machine to undergo inspection and cutter head changes.
Launch and retrieval blocks
When ground freezing is the method used for groundwater control and support of excavation for deep shafts, the freeze can be extended via additional freeze pipes to create a targeted stabilized mass for cutting of the eye for TBM launch or retrieval.