Tunneling & Construction in Wet Ground

Solutions

GEOFROST delivers safe and well proven solutions based on ground freezing technology, with focus on tunneling and construction in wet ground. The business areas are:

  • Tunnels for infrastructure and mining
  • Hydro power plant refurbishment
  • Municipal piping works
  • Civil works
  • Contaminated environment
  • Ground investigation

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Services

GEOFROST is a contractor delivering all services related to ground freezing and provides its clients with complete engineering solutions. The core services are feasibility studies, design, construction and management and the contractual interface is adaptable to the client’s needs. GEOFROST takes the full responsibility for its temporary structures.

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Safety first

Safety will always be our priority and something we never compromise on. It is crucial to our clients and the surroundings and a key factor in all our work.

Green technology

Sustainable solutions are important. The ground itself is used as the construction material. When mission is completed the unfrozen state is reestablished. We do not use any poisonous materials and our refrigerants do not affect the climate.

Social responsibility

We are a conscious part of the society and through our core values we take responsibility. GEOFROST shall never offer or accept a bribe or other improper payment for any reason.

Solid competence

GEOFROST is a specialized geotechnical contractor focusing on wet ground challenges and solutions by ground freezing technology. The company adopts modern technology and methods and is following possibilities in new developments.

GEOFROST has connections to academia, takes part in shaping technical standards and is represented in various technical societies. Specialist core competence, optimized equipment and a network of partners and suppliers provide high quality serivces.

Long experience

GEOFROST was founded in 1986 and has carried out numerous projects and gained invaluable experience within its business areas. Besides contracting, the company has done consultancy and research assignments and has also experience from the client’s side in large infrastructure projects.

Frost heave
Seasonal frost and AGF have different impact on the ground.

Frost heave requires that all of the following three factors are present:

  • Subfreezing temperature
  • Free access to water
  • Frost susceptible soil

Whether a soil is frost susceptible or not, depends on

  • amount of fines, i.e. mineral particles smaller than 0.02 mm
  • the ratio between the water suction rate to the freezing front and the frost penetration rate
  • the confining stress of the soil in the frost penetration direction
Thaw settlement
Seasonal frost and AGF have different impact on the ground.

Settlements due to thawing of frozen ground requires that both:

  • Frost heave/ice lenses has been created during freezing.
  • The excess water from melting ice cannot be absorbed by the ground.

Increase in pore pressure reduces the effective stress and settlements occurs if bearing capacity is exceeded.
Settlements will increase if loading is dynamic (for example traffic on thawing road after frost heave).

In seasonally frozen ground, excess water in thawing season is usual because underlying frost prevent drainage.

In artificially frozen ground, normally no ice lenses are created and thawing generally starts from the surrounding ground without any drainage barrier.

Quick clay
Their sensitivity must be taken into consideration in geo-design.

Water content of quick clay is generally higher than the liquid limit, representing potential settlements when released. There are mitigations that can be undertaken before freezing to avoid thaw setlements after freezing and thawing.

Warm climate
Freezing may be done in warm climate as well as cold climate.

Temperature has to be lowered from a higher level, but the transition from water to ice requires the same heat removal.

Back in 1995 GEOFROST did the first ground freezing project in Hong Kong, in connection with “The Strategic Sewage Disposal Scheme – Stage 1” on reclaimed land in Kowloon. The summer weather in Hong Kong is hot and humid. Average temperature is 28 °C, and the mean daytime temperature may often exceed 32 °C.

Water flow
Moving water represents extra heat to be removed.

If water flows through the volume to be frozen, there must be capacity enough to remove the heat added by the moving water in addition to the heat that must be removed to make the water transform into ice.

High water pressure
High pore water pressure doesn’t prevent the ground from freezing.

Both under high mountains and deep under the fjords, ground water pressure is high. These pressures are no problem for ground freezing. GEOFROST’s pore pressure record so far is 1400 kPa beneath the frozen cone in The Oslofjord subsea road tunnel.

Grouting in soil
Grouting for sealing below ground water level does not work in soil.

Grouting in rock fissures

The fissures may be regarded as a two-dimensional plan where the rock on each side gives confining resistance to grout penetrating it. The further from the injection point, the larger area to cover, and the pressure drops accordingly. This results in range limitations. The different grouting mixtures have different particle sizes and therefore different possibilities to penetrate the smaller/finer/thinner fractures. The grout goes where the resistance is lowest, larger fractures before smaller, smooth and plane fractures before rough and winding ones, all the time seeking the lowest hydraulic resistance. Grouting generally works very well when dealing with fractures in rock. Pregrouting is the dominating mitigation for tunneling in Norway, where major parts of the tunnels are in hard rock.

Grouting in soil

The pore volume in soil may be regarded as a three-dimensional medium. The grout is spread as an expanding “spherical plane” instead of a “spherical circumference”. For this reason, the pressure drops much faster in soil than in rock fissures, as distance from the source increases. The pores in soil are the voids in-between each of the grain particles. The pores are connected through tiny passages where the grains do not have contact with each other. The grout that penetrates where the resistance is lowest, will have difficulty penetrating the grain skeleton evenly and fill all the voids.

Photo: Grout is orange in sample.

Photo: Grout in fines.

When the ground “does not take grout”/the grout does not penetrate, it will neither be able to waterproof or improve the ground strength in general. In sand, silt and clay, grout cannot be forced into the pores by pressure, even at great depth with high confining pressure. If pressure is increased, there will be hydraulic splitting and the grout will follow the created fissure/the widest passage instead of evenly filling the pores.

AGF

On the other hand, artificial ground freezing penetrates all geolocical formations, independently of permeability, providing stabilization and water-proofing.

Temporary plugging
After the need for plugging disappears, the ice plug is melted away.

The ice plug concept developed by GEOFROST is based on two facts:

  • materials are gaining strength when frozen and
  • the sealing may easily be removed after use.

The concept is ideal for temporary works in connection with maintenance and refurbishment in water filled hydro tunnels and the method has low impact on the environment.

During research, the worlds first ice plug was created, holding back one of Statkraft’s hydro power reservoirs at Røssåga.

Behind the ice plug at Røssåga.

The ice plug concept has also been successfully applied to the headrace tunnel at Skoddeberg for Hålogaland Kraft.

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