Hydropower tunnels

Safe refurbishment work in hydropower tunnels.

Contracting services

Ice plug from surface

Geofrost provides ice plugging of water tunnels upstream the first gate, in order to empty the tunnel for water and carry out refurbishment works in a safe manner in a dry tunnel.

Drilling is performed from surface above the reservoir level and down through the tunnel. Freezing pipes and monitoring equipment are installed in the holes.

Ice plug is used because a cofferdam is not always easy to establish. It may be due to topography, regulations for the lake, or large values being lost for the owner if the water level is lowered.

Ice plug, Skoddeberg hydropower plant.

Ice plug from waterside

Geofrost may install the ice plug through the water intake if the headrace tunnel is a pipe or an intake structure that preferably should not be drilled through, or it is not practical to drill into the tunnel.

The ice plug has high reliability and is frozen into the surronding rock or concrete lining. The ice plug is monitored as long as it is functioning and detailed capacity calculations are always part of the design.

Photo: Ice plug.


Figure: Cofferdam.

Geofrost provides a waterproof core in rock fill dams to create a cofferdam. Drilling is done through the rock fill and further down through permeable layers and fractured rock, ensuring a completely impermeable cofferdam.


No lowering

By plugging the water filled tunnel by a Geofrost ice plug, it may become unnecessary to lower the reservoir water level.

Minimal stop

The temporary ice plug is relatively quick to establish, and removal is even faster. Time without hydro power production is minimized.

Low impact

Installation of the ice plug has low impact on the surroundings.

What we deliver

We are a total supplier of ice plugs and waterproofing of cofferdams with ground freezing and offer all related services within consulting and contracting.


  • Project management
  • Design and engineering
  • Numerical analyses
  • Design report, drawings, and specifications.


  • Planning and procurement
  • Site management
  • Drilling and surveying
  • Pipe installation
  • Plant and equipment for brine and nitrogen freezing
  • Instrumentation
  • Monitoring

Where we operate

We offer our services worldwide.


Contact person

Anne-Lise Berggren, Ph.D., M.Sc
Senior specialist geotechnics
(+47) 95 29 29 30


If you have questions or would like more information, please contact us. With project info, we quickly provide price estimates.

Ground freezing since 1986.