Ground freezing for shaft sinking and temporary tunnel support

Waterproof temporary support for
both D&B and TBM
Full face drill and blast tunneling through soil and weakness zones. More even load on TBM head.
CONSULTANT AND CONTRACTOR.
Specialized on AGF since 1986.

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

Foto: Shaft.
We deliver temporary ground freezing, to securely drive shafts through water bearing strata down to minerals for mining or underground space.

Shaft for minimg

Figur: Shaft sinking for mining, stailized by ground freezing.

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

Figur: Shaft for tunnel ventilation stabilized by ground freezing.

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

Figur: Soil tunnel stabelized by ground freezing.

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.

Foto: Soil tunnel stabelized by ground freezing.
Geofrost delivers temporary support to enable soil tunneling efficiently with full face excavation. Keeping the water away also secures good quality concreting. Ground freezing provides safe and efficient tunnneling and the frost is maintained until loads may be transferred to the permanent lining.

Weakness zone

Figur: Stabilizing weakness zone by ground freezing.

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).

Foto: Ground freeezing for drill and blast tunnel through weakness zone.
Geofrost deliver temporary stabilization and waterproofing to enable efficient tunneling through weakness zones or zones with potentially large water leakages. Tunneling should stop for mitigation before trouble starts.

Mixed face

Figur: Ground improvement by ground freezing for mixed face tunnel excavation.

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.

Foto: Pilot tunnel under area with lack of rock overburden, stabilized by ground freezing.
If it is possible to install the ground freezing from surface or a nearby tunnel, ground freezing stabilization is ready when tunnel face arrives the critical zone. Otherwise the ground freezing is installed from tunnel face.

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

Figur: Access to rock tunnel through soils stabilized by ground freezing.

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.

Foto: Acess to rock tunnel through soil stabilized by ground freezing under retainnig wall.
Issues that are avoided:
  • 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

Figur: Frozen block for TBM starting pit in soil.

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.

Foto: TBM starting to run through frozen soil behind a diaphragm wall.
Geofrost delivers starting blocks by ground freezing which secures both stability and impermeability where the TBM enters the ground.

Cross passage

Figur: Ground freezing to stavilize CP excavation in soil between two TBM excavated tunnels.

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