Artificial ground freezing converts in situ pore water to ice by circulating chilled liquid through small-diameter freeze pipes installed in drilled boreholes. The process creates a strong, impermeable frozen soil mass for temporary excavation support and groundwater control, especially in saturated soils.
Process
Artificial ground freezing for groundwater control and excavation support was developed more than a century ago and remains a proven geotechnical solution for challenging underground construction. It is most effective where both excavation support and groundwater cut-off are required, particularly for deep excavations, shafts, tunnels, and projects in difficult, disturbed, or sensitive ground.
The ground freezing process begins with an integrated design that accounts for the mechanical, thermal, and hydraulic properties of soil and groundwater. Closed-end freeze pipes are drilled and installed around the excavation perimeter or within the treatment area. A smaller pipe inside each freeze pipe circulates refrigerated fluid, typically calcium chloride brine, through a closed system. No chemicals are injected into the ground or groundwater. After four to eight weeks, the frozen ground becomes water-resistant and gains the strength needed to support excavation. For small-scale or emergency ground freezing, liquid nitrogen can be used to reduce freezing time to two to three weeks.
Specialist contact
Joseph Sopko, PhD, PE is Director, Ground Freezing at Keller North America.
Joe Sopko received his BSc, MSc, and PhD in Civil Engineering from Michigan State University. He has more than 40 years of experience in all aspects of design and laboratory testing programs related to underground construction projects. He develops business opportunities related to geotechnical construction, specifically ground freezing and groundwater control, and routinely provides on-site project management and quality control programs. He has designed and managed ground freezing projects worldwide, including forming laboratory-frozen soil testing programs, numerical modeling, and on site quality control and assurance. He has completed over 100 projects, including deep shafts, tunnel adits, cross passages, and emergency TBM recoveries.
Dr. Sopko specializes in ground freezing for civil and mining projects worldwide. He is also an adjunct professor at Michigan State University. He served with the U.S. Air Force as an engineering officer in Afghanistan and Operation Deep Freeze in Antarctica.
Common uses
- Temporary earth support and groundwater control for deep shaft excavations
- Support of excavation and groundwater control for tunnels and adits
- Groundwater barriers and freeze walls for underground construction and mining projects
Advantages
- Proven groundwater control and excavation support solution for complex underground construction projects
- Can be performed at significant depths, including deep shafts and tunnels
- Can be used in heterogeneous, disturbed, or sensitive ground where conventional methods may not be feasible
Related projects
Tunnels and shafts
Boston Central Artery Tunnel
Three tunnels were to be created beneath seven active Amtrak lines serving Boston’s South Station and the financial district.
Tunnels and shafts
Eastside CSO
The East Side Combined Sewer Outflow (CSO) Tunnel project consisted of the construction of approximately 29,000 linear feet of tunnel, seven shafts and multiple pipe-line connections.
Tunnels and shafts
Port of Miami Tunnel
The Port of Miami Tunnel project consisted of a twin tunnel bored through the coral below the Port of Miami, Florida.
Mining
Kansas Underground Salt Museum
The Hutchinson salt mine is an active salt mine in the United States with an underground museum open to the public. Ground freezing ensured dry and stable excavation of the new elevator shaft.
Infrastructure
No. 7 Subway Line Extension
When incompetencies in the rock were discovered, Keller was contracted to perform several techniques from their tunneling toolbox to keep operations on track.
