Artificial ground freezing is a technique used in constructing shafts, mines, and tunnels to provide temporary earth support and groundwater control when other conventional methods such as dewatering, shoring, grouting, or soil mixing are not feasible.
Ground freezing also provides regional groundwater barriers around mining operations for gold and other minerals, oil sands, or oil shales. It is often referred to as ground freezing, soil freezing, or freeze wall. Ground freezing involves drilling, installing a series of relatively closely spaced pipes, and circulating a coolant through these pipes. The refrigerated coolant extracts heat from the ground, converting the soil pore water to ice, resulting in an extremely strong, impermeable material. It is the most positive ground improvement method used in the underground construction and mining industries.
Ground freezing is successful when completed by experienced contractors who have the required specialized equipment. It is an interactive process requiring advanced engineering, accurate drilling, as well as custom-made refrigeration and instrumentation equipment.
Ground freezing applications
Deep shafts are the most common application of ground freezing. The freeze pipes are drilled and installed around the perimeter of the proposed shaft to the required depth. The coolant is circulated until a frozen zone from 1 to 10 meters is formed. The inside of the shaft is then excavated and lined, and the freezing system is turned off.
Ground freezing is used extensively in the tunneling industry. Tunnel applications use several different approaches. The most common involves horizontally drilling the freeze pipes around the tunnel perimeter, similar to the frozen shaft approach. This horizontal configuration is used to tunnel beneath roads or railways or to construct safety cross passages between two existing tunnels. Another method of constructing tunnels is to freeze the entire alignment solid and mine through a frozen mass of soil. This approach is often coupled with the Sequential Excavation Method (SEM) and used for small-diameter tunnel adits.
Ground freezing is also used with Tunnel Boring Machines (TBMs). The ground in front of or around the TBM can be frozen in advance to create a pre-planned safe haven for tunneling interventions or used in emergencies for TBM repair.
Ground freezing has been proposed for regional groundwater barriers up to 10km long to isolate groundwater from mining operations instead of large-scale dewatering operations with environmental consequences or requiring complex and expensive treatment operations.
Key contacts
Joseph Sopko, Ph.D., P.E.
Director of Ground Freezing, Keller North America