Benefits
Safe and predictable
Ground freezing is in general a reliable solution, well known for its safety. Both client and contractor can trust in predicted time and cost, and the very low risk element even with complex and complicated ground conditions.
The temporary support by ground freezing gives a safe working environment protected by stabilizing frozen structures. The frozen structure is surveyed and will have a slow melt down in case of energy interruption, and a plastic failure mode.
Ground freezing works in all types of soil and rock, independent of fracture size, permeability, water content, water pressure, degree of rock degradation, block content or grain size.
Completely impermeable
The underground is stabilized by ground freezing and becomes completely impermeable, resulting in dry working conditions in the tunnel and no pore pressure drop in the surroundings. There will be no need for water wells for supplying groundwater to keep up pore pressure. No grouting by cement or chemicals. The ground is kept frozen until the permanent structure is brought in place. By eliminating any water leakages, there is no need for drains behind the concrete and a good concrete quality is secured.
Ground freezing is installed proactive, before any failure or water inrush has occured. To keep the pore pressure unaffected, drilling from below groundwater level is performed through a blow out preventor (BOP). If the surroundings are highly sensitive, drilling is done with mass control as well.
Environmentally friendly
It is the ground itself creating the temporary supporting structure. No cement og chemicals are used in the ground. Coolant and refrigerant are natural media, without any effect on the climate (0 GWP). The CO2 footprint is very low compared with other steel and concrete based methods.
Efficient tunneling
Geofrost's ground freezing structure is designed for full face excavation. Typical blast rounds are 2 m full face, which will include less supporting materials and a faster excavation than a solution with more faces in the cross section. Concreting directly against the frozen walls, without any leakages will speed up the excavation and support the robustness in time and quality.
The frozen structure takes the load until a permanet structure is ready to take over. By interaction between frost and sprayed concrete with lattice girders put up as work support after blasting, necessary thickness of the frozen structure can be reduced and thus also initial freezing time and cost. Permanent lining is achieved by additional layers of sprayed concrete, or cast in place concrete or concrete elements put in place and grouted behind.
When installing ground freezing from surface, the frozen structure is estabilished in advance such that it is ready when tunneling reaches the zone. Drilling may be done vertically or inclined from the best locations. Freezing pipes may be insulated so only the needed volume is frozen. By drilling from above groundwater level, all issues connected with pore pressure reduction and settlements in the surroundings are avoided.
Products
Geofrost cylinders stabilizes before excavation and keeps the water out.
Shaft
Shaft for minimg
Ground stabilization through water bearing strata by ground freezing to secure shaft sinking. The often long holes for freezing pipes may be drilled by directional drilling to secure the necessary accuracy. Shafts for mine access may be couple of hundred meters deep, and are lined as excavation proceeds. The circular shape of the frozen wall exploits the high compression strength of frozen materials. Excavation may start when the inital freezing has grown a sufficiently thick structure for the top layers. While excavating and lining the top part, the deeper part has time to grow thicker and thus take the larger forces that are present at larger depths.
Shaft for tunnel ventilation
Ventilation shafts running from surface to a tunnel for supply of fresh air may be several tens of meters. The shaft generally has to pass through soil and fractured rock before sound rock is reached above the tunnel. We supply impermeable shaft stabilization through soil and waterbearing formations. Stabilization and waterproofing by one method covering all ground conditions.
Soil tunnel
When the ground is to weak to be self supporting, ground improvment is necessary to secure the excavation. Water leaks may also increase instability. Even the tunnel invert may be squeezed upward due to water pressure or larger horizontal stress in the ground. Complete ground freezing cylinder secures the tunnel excavation. Even the whole cross section may be frozen to secure face stablity and avoid water leakage through the front.
Weakness zone
Rock tunnels in generally competent rock, usually also need to cross some weakness zones where rock quality is insufficient for safe tunneling without any mitigations, either for drill and blast tunneling (D&B) or tunneling with tunnel boring machine (TBM).
Mixed face
The rigid alignment of modern infrastructure projects often results in some part of the tunnels do not have enough rock overburden, when best geometrical alignment is choosen.
Geofrost delivers stabilization where rock overburden is missing for drill and blast to go through with full face excavation, or ground improvement of weak ground such that the TBM has more even load on the drillhead. The stabilization by ground freezing and achieved impermeability avoids failures, sinkholes and surface settlements.
D&B starting point
Tunnel excavation by drill and blast generally starts when the rock overburden is large enough to be part of a self-supporting arch. Geofrost deliver ground freezing to enable this arch to start at the surface, avoiding large excavations and a deep construction pit.
- slope stability problem
- removing houses on top
- rerouting of crossing roads
- excavation of large volumes that need to be transported, deposited and than brought back to cover a cut and cover portal
- affecting the landscape area and natural groundwater level of the area
Geofrost improves the ground from surface until rock overburden is sufficient for normal drill and blast excavation. This minimizes the open cut and avoids the metioned possible disadvantages.
TBM starting pit
EPB machines are an alternative to cut and cover when constructing soil tunnels. A construction pit is constructed for lowering the head and tail to right level, and a starting block is established behind the retaining wall, to avoid soil and water inrush when hole is made in the retaining wall.
Cross passage
Infrastructure tunnels today are often built as two parallell tunnels, with cross passages for example every 500 m. Ground improvement and water sealing is necessary in soft ground in urban areas.
Geofrost delivers ground freezing to stabilize while constructing the cross passage, and at the same time sealing against water inflow to the excavation and pore pressure reduction in the surroundings.
What we deliver
We are a total supplier of temporary impermeable tunnel support, and offer all related services within design and construction, as well as ground investigation with undisturbed soil sampling of frictional soils, rock fracture filling and more. Tunnel support ready designed, installed and maintained as long as needed.
We deliver temporary support for shaft and tunnels through water bearing ground and weakness zones, ground freezing for soil tunneling, easy start for both drill and blast tunneling and TBM tunneling as well as stabilization of cross passages.
Consulting
- Project management
- Sampling
- Lab testing
- Design and engineering
- Numerical analyses
- Design report, drawings and specifications
Contracting
- Planning and procurement
- Site management
- Drilling and surveying
- Pipe installation
- Plant and equipment for brine freezing and nitrogn freezing
- Instrumentation
- Monitoring
Where we operate
We offer our services worldwide. Equipment is containerized and ready for worldwide transportation.
Contact
Contact person
Anne-Lise Berggren, Ph.D., M.Sc
Senior geotechnical specialist
(+47) 95 29 29 30
Anne-Lise.Berggren@geofrost.no
Enquiry
We have competitive prices that match other methods. With brief project info, we quickly provide price estimates on request.
Clients
