Ground freezing

Ground freezing is a state-of-the-art construction method that significantly reduces impacts on the subsoil and the surrounding area. This method is used, for example, when construction schemes in built-up areas make boring from the surface difficult or even impossible. It eliminates vibrations that could endanger existing buildings. Ground freezing is primarily used in underground construction/tunnelling.

Common uses for ground freezing include:

• Temporary sealing and/or support while building tunnels, especially for cross-cuts and junctions
• Producing and/or sealing shafts or construction pits
• Securing existing buildings (underpinning)
• Preparing the soil for undisturbed sampling, e.g. core drilling
   

• Salt brine-based ground freezing is a closed system, making it environmentally friendly.
• Minimally invasive and vibration-free
• Safe and tested method with comprehensive monitoring
• Does not require groundwater lowering
• Low spatial requirements
• No disruption of aboveground traffic
• This is frequently the only option that is technically feasible
  (e.g. for the construction of cross-cuts in tunnelling).
• Safety during execution is monitored by applying high quality assurance standards.
   

Secure sealing and soil stabilisation

Ground freezing involves temporarily solidifying and waterproofing the subsoil by artificially freezing the soil water. The resulting frozen mass makes the subsoil exceedingly stable and provides protection against any influx of water until these functions can be taken over by the building structure later on.

After the construction work is completed, the ground thaws naturally. Apart from the freeze lances installed in the ground before freezing, soil freezing does not leave any artificial additives in the subsoil and is therefore one a minimally invasive method.

Precision work: Drilling accuracy is the key to success

The success of ground freezing fundamentally depends on the boring technique used for the freeze boreholes. The freeze boreholes must be placed with maximum accuracy and the drill strings sunk with maximum impermeability. Other technical challenges include drilling under pressure from groundwater and in confined workspaces. PORR has the special boring equipment and proven drilling and preventer techniques necessary to carry out this construction task safely and economically with its own experienced specialist team.

We ensure high execution quality with:

• Individually coordinated instructions
• Monitoring the boring accuracy, e.g. by means of an optical deflectometer
• Monitoring the temperature curves in temperature measuring lances inserted in the soil
• Monitoring the brine circuit parameters (e.g. system pressures, flow rates, temperatures)
• Clear processes governed by our quality management system in accordance with DIN EN ISO 9001:2015
   

Two different freezing methods and refrigerants are available:

Brine freezing

• The refrigerant is a CaCl salt solution.
• Working temperatures down to -37 degrees C
• The brine circulates in a closed circuit and is treated by a freezing unit.
• High economic efficiency, which makes the brine process suitable for longer applications
   

Nitrogen freezing

• Ground freezing using liquid nitrogen
• Working temperatures  down to -196 degrees C
• The target ground can be frozen quickly.
• Can also be used where there are rapid water currents in the groundwater
• Particularly suitable for short-term special applications, also in combination with brine freezing