Soil freezing gets a warm reception here
New approach makes freezing easier to do, less expensiveBy JAMES MILLER
If you've ever tried to dig a hole in the ground after an extended period of sub-freezing weather, you know how tough frozen soil is. It has nearly the strength of concrete and nothing passes through it not water, chemicals or hazardous materials.
That's the concept behind the latest applications of ground freezing, a cool technology for construction shoring, control of groundwater and isolation of subsurface contamination.
Wherever soil is loose, soft or wet, ground freezing can be used to create a safe, simple, reliable and surprisingly cost-effective barrier, either as a temporary application or a permanent solution.
An old idea
Ground freezing has been around for about 100 years, but was usually ruled out as being too expensive for all but the largest construction projects. Recently, however, RKK-SoilFreeze Technologies, LLC, a Redmond-based specialty contracting company, has developed a modular approach that puts ground freezing benefits within the reach of everyday construction projects.
To freeze soil, pipes are installed several feet apart around the perimeter of the area to be excavated or contained. Chilled brine is circulated through the pipes, freezing the surrounding soil. Within two or three weeks, a frozen wall develops along the alignment of the pipes. The frozen wall can serve as high-strength construction shoring as well as a barrier to prevent migration of groundwater.
When the project is complete, the soil gradually thaws and reverts back to its original unfrozen condition. Alternatively, the frozen wall can remain in place indefinitely.
Ground freezing is ideal for a multitude of construction and environmental applications. It's effective in almost all soil conditions, including running sand, cobbles, peat, clay and bedrock. It provides excellent flexibility for sites with buried utilities, as the freeze pipes can be installed around or beneath existing underground facilities.
Soil freezing equipment is small and uncomplicated to install, making it is easy to adapt to difficult or remote sites. Power outages during construction are not a problem either, because frozen ground stays frozen for days to weeks without additional chilling, even in the summer. And at between $15 and $25 per square foot, the price of a frozen soil wall is much more attractive than many other options.
Many market forces contribute to the current enthusiasm for ground freezing. One is that groundwater management and control have become more problematic because of increased regulatory requirements in numerous Western states. Often it is not possible to remove and dispose of large volumes of groundwater, even for temporary construction purposes. Those problems are multiplied if the groundwater is contaminated.
Also, construction sites are more congested and complicated than they used to be. Many contractors must work around existing infrastructure, such as tunnels, cables, sewer lines and other utilities, prohibiting the use of conventional shoring with sheet piles. A frozen soil barrier, on the other hand, often can be installed without disturbing underground infrastructure or requiring expensive relocation of utilities.
A third trend driving the move toward ground freezing is the presence of contaminated water and soil at many construction sites. The Growth Management Act mandates clustered development throughout Washington, so projects are often sited in former industrial areas rather than on virgin land.
Treating and hauling off hazardous materials or contaminated groundwater is a pricey proposition. But a frozen barrier can be installed on a temporary or permanent basis, safely isolating a work area from external contaminants or preventing the migration of contaminants to new locations.
The Port of Seattle used ground freezing to support soil while repairing a storm sewer at Terminal 5. Tri-State Construction deployed the technology for a METRO project in Renton to construct an underground receiving pit for a tunnel boring machine and to recover a tunneling machine that had become disabled at a depth of about 30 feet. And the basement excavation for a condominium being constructed alongside Lake Washington was kept dry with a frozen soil barrier.
Ground freezing for the isolation or containment of subsurface contamination is an exclusive offering of RKK-SoilFreeze Technologies, which is owned in part by GeoEngineers. The patented technologies used for isolation of subsurface contamination were developed, tested and patented in cooperation with scientists at the University of Washington.
The Department of Energy has named soil freezing as one of the top five new technologies for containing high-level radioactive and mixed waste materials at its facilities throughout the United States, including Hanford.
GeoEngineers considers its investment in RKK-SoilFreeze Technologies to be very strategic because the technology leverages the company's existing geotechnical skills and offers unique benefits to its environmental and construction client base.
Since GeoEngineers typically performs engineering design work for subsurface systems, the ground freezing application is a logical add-on service, and one that can be expected to generate considerable business and revenue growth.
Although this is only the second year in business for RKK-SoilFreeze Technologies, word is already spreading fast about its capabilities.
Queries are coming in from as far afield as Peru and the company expects to complete more than $3.25 million in new ground freezing projects during 1999.
James Miller is president and CEO of GeoEngineers, a geoscience consulting firm in Redmond.
djc home | top | special issues index