Below are the first 10 and last 10 pages of uncorrected machine-read text (when available) of this chapter, followed by the top 30 algorithmically extracted key phrases from the chapter as a whole.
Intended to provide our own search engines and external engines with highly rich, chapter-representative searchable text on the opening pages of each chapter.
Because it is UNCORRECTED material, please consider the following text as a useful but insufficient proxy for the authoritative book pages.
Do not use for reproduction, copying, pasting, or reading; exclusively for search engines.
OCR for page 171
Artificially Frozen Ground as a Subsurface Barrier
Technology
Steven A. Grant and Iskandar K. Iskandar, Cold Regions Research and Engineering
Laboratory, U.S. Army, Harlover, New Hampshire
INTRODUCTION
Frozen water-saturated ground has great mechanical strength and very low permeability.
These properties are exploited by construction ground freezing, a mature civil-eng~neering practice
that has long been used in North America, Europe and Asia, usually to restrict ground-water
seepage or~stabilize the walls during excavations. Construction ground freezing is often competitive
economically with other hairier methods; its principle disadvantage is the long time it can take to
form a frozen wall. Recently, artificial ground freezing has been used to form barriers at
contaminated sites. The principle advantages of artificial ground freezing for this application, which
we designate here as "environmental growing freezing." are thought to be its ability to form
a, -
impermeabie banders across transitions from soil to bedrock, the minimal amount of solid material
hrnu~ht to or taken from the site duIina battier construction or decommissioning, and the great
a
flexibility in designing or adjusting the ba:Tier's size and shape (]iskandar and Jenkins, 19651. Some
believe that, as a natural process, soil freezing is likely to find public and regulatory acceptance,
although the technique has been implemented at too few contaminated sites to judge this belief.
PHYSICS, CEIEMISTRY AND MECHANICS OF FROZEN GROUND
Frozen ground is composed of four phases: gas (often as entrapped bubbles), liquid
aqueous solution, solid ice, and solid mineral matnx. A schematic of this assemblage is presented in
Figure 1. The amount of liquid aqueous solution remaining at a particular temperature is
determined by two physical-chemical phenomena: interracial forces caused by the distortion of the
ice-solution interface as it is forced to adjust itself to the geometry of the ground's mineral matrix;
and colligative properties of the water as a solvent, that is, the freezing-po~nt depression of the pore
solution. Of the two, interracial forces are the more important In determining the amount of liquid
aqueous solution persisting at subzero temperatures in ground. As would be expected, the larger the
specific surface area of the minerals, the larger the fraction of water remaining unfrozen at subzero
temperatures. Figure 2 presents the calculated volumetric liquid-water content of a water-saturated
Royal sandy loam as a fimction of temperature. Due to freezing-point depression, the presences of
solutes in the pore solutions will cause the amount of liquid present at a given subzero temperature
to be increased. This can become an important consideration when ground saturated with seawater
is being frozen.
The amount of liquid water remaining in frozen ground is not solely of academic interest.
In many cold regions, it is this liquid fraction that wicks water Tom deeper in the soil profile to the
ground's freezing Font, causing Cost heaves--a serious engineering problem. Liquid-water contents
of frozen ground affect the ground's strength, its permeability, and the diffusion rates of solutes in
D-153
OCR for page 172
D-154
BARRIER TECHNOLOGIES FOR ENVIRONMENTAL MANAGEMENT
it. All of these could be factors in determining the suitability of environmental ground freezing at a
given site.
Gas Unfrozen
Bubbles Water
/ /
~ Amp I N~ \ ~
t
Vg
a. Natural Soil
Vi
V
Vs
t ,
vw
. ~
b. Soil Separated into Phases
FIGURE 1 Schematic drawings showing the phase distribution in Dozen ground.
~ 0.3
Cal
-
~ .
o 0.2
Cl'
0' 0.1
o
Wg
Ww
Ws
Wj
-25 -20 -15 -10 -5 0
W
Temperature (C)
FIGURE 2 Calculated relationship between temperature and liquid water in a frozen Royal
sandy loam.
OCR for page 173
APPENDIX DIAPERS PRESENTED
D-155
Mechanical Properties
The strength of frozen ground is due to the strengths and volumetric fractions of its
constituents: ice, mineral grains, and liquid water. By most measures, frozen ground can be a very
strong material. The measured unconfined compressive strength of frozen Ottawa sand at -50°C
was 40 MPa (Sayles, 19881. The corresponding strengths of competent granite without macroscopic
flaws are between 150 and 250 MPa. The resistances of frozen ground to load and deformation are
affected by its mineral composition, water content, temperature, previous loading, and rate of
loading. The effect on the proportion of water is presented in Figure 3. As a general rule, the
resistance of frozen ground to load and deformation increases with decreasing temperature but
decreases with fume. These two tendencies are shown In Figure 4, which is reproduced from Sayles
(19881.
Permeability
The permeability of frozen ground can be estimated based on the ground's degree of
saturation by liquid pore solutions. Figure 5 presents the calculated permeabilities of a Royal sandy
loam as a function of temperature.
ARTIFICIALLY FROZEN GROUND AS AN ENGINEERING TECHNOLOGY
Many, including practicing civil engineers, are unaware of construction ground freezing,
yet it is hardy a secret. Perhaps the most famous structure to be affected by construction ground
freezing is the tower in Pisa, Italy, the foundation of which is being stabilized by the technique
while a more permanent solution to its inclination is being constructed. Perhaps the largest
construction project to use construction ground freezing was the Tokyo Metro. A total vo! Me of
38,000 ma of material was excavated (lessberger, 19801.
In 1883, the technique was patented by F.H. Poetsch in Germany as a mine-shaft
construction method. While improvements have been made, the techniques used today are
essentially those of Poetsch. Energy is removed from the ground by circulating cold liquids through
pipes drilled into the ground. The two refrigeration approaches are: using a mechanical refrigeration
plant through which a heat-transfer fluid is circulated to freeze pipes, or pumping expendable
cryogenic liquids through the freeze pipes. Freeze pipes, which consist of two nested pipes for
supply and return of the heat-transfer fluid (usually CaCI2 or MgCI2 brines) or cryogenic liquid
(typically liquid nitrogen), are drilled into the ground at regular intervals, typically ~ m.
In principle, any soil can be frozen. Shuster (1980) noted that successfi~l implementation of
ground freezing may be limited as follows:
1. The degree of saturation of the ground by water must be high enough to bind the sol!
grains when Dozen. Generally, fully water-saturated ground is preferred.
2. The concentrations of solutes in pore-water solution should not be too high. This is a
consideration, for example, when freezing marine sediments. The melting point of sea ice is lower
and its strength less than that of fresh-water ice. (There have been instances of catastrophic failures
OCR for page 174
D-156
I,
~6
LO
-
it,
~ 4
lo
o
~ 2
~
4
o
BARRIER TECHNOLOGIES FOR ENI'IRONMENTAL MANAGEMENT
;
en' ~
·\
O
am_
· GO~;FNOUR ANI) ANDERSlAND, 1968 -
° BAKER, 1979
0 20 40 60 80 100
TOTAL MO I STORE CONTENT, %
FIGURE 3 Effect of total moisture content on unconfined compressive strength of a frozen
fine sand at -12°C and at a strain rate of 2.2 x 10-6 s~i (Dom Andersland and Ladanyi, 19941.
10
-
CL
A. 8
Strength from test data. '3
-- Predicted strength from Vialovs eat: ~u''~ ~,n`~/B'
. .. (1500hr)
. ._
(4000 hr.)
1 . . . ~-0.6 1 ~(2000 hr.)
0 100 200 300 400 500
I, Time (mint)
FIGURE4 Calculated relationship between temperature and hydraulic conductivity of a
frozen Royal sandy loam.
OCR for page 175
APPENDIX~PAPERS PRESENTED
10-3
10-4
10-5
10-6
no 10-7
.E
C'
~ 10-9
._
._
co
E
a)
10-8
1o-1o
0-11
0-12
1o-l3
10-14
10-15
10-16
10-17
-25 -20
D-157
-15 -10
Temperature (C)
-5 0
FIGURES Calculated relationship between temperature and hydraulic conductivity of a
frozen Royal sandy loam.
Of frozen walls formed in salt-water saturated ground [E.~. Chamberlain, personal communication,
199411.
3. Ground-water seepage does not bring to the forming barrier more energy than can be
removed by the refrigeration plant. Calculations have shown that flows should not be greater than 2
m/day. The ground has comparatively high heat capacity and low thermal conductivity (Sullivan
and Stefanov, 19901. Once formed, a frozen-ground barrier effectively eliminates energy loss due to
convection and can be maintained indefinitely with Tow power consumption.
There is a small, but stable market for construction ground-freezing services; four firms in
the United States provide the service.
ARTIFICIALLY FROZEN GROUND AS A WASTE-CONTAINMENT TECHNOLOGY
We are aware of two contain" inated sites at which artificial ground freezing is being used
for waste containment. The first is a National Priority List (NPL) site in the eastern United States
situated next to a river. Frozen ground walls are being formed in conjunction with sheet-pile walls
to limit the migration of contaminants off-site to the river. This site will be excavated after the walls
OCR for page 176
D-158
BARRIER TECHNOLOGIES FOR ENVIRONMENTAL MANAGEMENT
are formed. The second site is a petroleum-contaminated site on permafrost in Alaska. Here a
frozen-ground bander has been formed to prevent snowmelt-runoff driven horizontal flows of
dissolved petroleum products as the active layer above the permafrost thaws.
Ground freezing has been proposed, though not as yet adopted, at two DOE reservations:
Oak Ridge and Hanford. A successes! field trial was conducted at Oak Ridge in 1994. The soils of
the Solid Waste Storage Areas within the Oak Ridge Reservation (ORR) are fairly shallow (3-9
feet), weakly developed, and overlay weathered rock (saprolite). Environmental ground freezing is
seen as having two potential advantages at ORR. First, the barrier can be formed continuously
across the transition Tom soil to the underlying saprolite. Second, when compared with other
methods, less earth will be excavated In Installing a ~ozen-ground baITier. Environmental growing
freezing has also been proposed at the Hanford Reservation, although an unrealistically Tong time
may be needed to develop a reliable technique to saturate and cool an arid soil simultaneously,
without water loss. Results of bench-scale experiments, however, are encouraging (AndersTand et
al., 1994; Dash et al., 19941.
SCREENING MATRIX
Development Status
Construction ground freezing is routine, but environmental ground freezing is in its
infancy. The firms that participated in the environmental ground freezing projects and
demonstrations have been able to meet the design criteria without difficulty. A principle difficulty
appears to be that there is no ~n-situ sensing technology for continual assessment of the integrity of
the barrier. As with other barrier technologies, sensing leaks Tom beneath the barrier are
problematic.
Ava;RabiJity
As noted above, a limited number of firms provide this service, which is as much an art as
a construction practice. Were the demand for environmental ground freezing to increase markedly,
experienced practitioners could be finely booked. This appears to be a hypothetical, not imminent,
problem.
Implementability
At sites that meet the criteria for successful Implementations of construction ground
freezing, one would expect that environmental ground freezing could be implemented
straightforwardly.
OCR for page 177
APPENDIX~PAPERS PRESENTED
Reliability/Maintainability
D-159
Based on experience with construction ground freezing, the technology should be reliable
and easily maintained when installed professionally at an appropriate site.
Secondary Waste Produced
Intrinsically, very little secondary waste is produced with environmental ground freezing.
Stance the method typically relies on water in the ground, only that material brought to the surface
for drilling holes for freeze pipes may constitute a secondary waste. Once refiigeration is stopped,
the ground returns largely to its original condition, although frozen ground may consolidate while
thawing.
Implementation Costs
These tend to be high but are competitive with other battier technologies (Sullivan, Lynch,
and Tskandar, 19841.
Operating Costs
Although dependent on the intensity of on-site monitoring, these costs should be modest.
Regulatory Acceptance
As an organization that supports environmental research, the U.S. Environmental
Protection Agency (EPA) has fended some studies and demonstration projects, but it has not
indicated how readily it will accept environmental ground freezing.
Public Acceptance
Environmental ground freezing has been implemented at very few sites. To our knowledge,
no studies of public acceptance have been made. it is assumed that environmental ground freezing
should not incite public resistance since it is an adaptation of a natural process.
Natural Resources Impact
Extended periods at subzero temperatures would kill many of the flora and farina remaining
In the frozen-ground barrier. As noted above, forming the frozen-ground barrier takes roughly a
month; presumably, most of the burrowing animals would vacate the barrier as it cools. Rapid re-
habitation from the surrounds after decommissioning of the barrier would be anticipated.
OCR for page 178
D-160
Risk-Management Reduction
BARRIER TECHNOLOGIES FOR ENVIRONMENTAL MANAGEMENT
It is expected that the risk-management effects of environmental ground freezing would be
on par with other hairier techniques.
CONCLUDING REMARKS
Environmental ground freezing has long been a promising waste isolation technology but
one that was all too rarely fielded (Bovay Northwest, Inc., 19921. Recent evaluations and
implementations at contaminated sites may yield a sufficient body of experience so that the
technique may be implemented more often.
REFERENCES
Andersland, O. B., and B. Ladanyi. 1994. An Introduction to Frozen Ground Engineering. New
York: Chapman and Hall.
Andersland, O. B., S. H. Davies, and D. C. Wiggert. 1994. Performance and Formation of
Cryogenic Containment BaIriers in Dry Soils. Report Submitted to RUST Geotech, Inc.,
Grand Junction, Colo.
Bovay Northwest, Tnc. 1992. Interim Subsurface Barriers Technologies. Workshop Report.
Prepared for Westinghouse Hanford Company, Bovay Northwest, ~c., Richland, Wash.
Dash, J. G., H-Y. Fu, and R. Leger. 1994. Bench Ccale Testing of Hanford and Oak Ridge Soils,
Formation and Diffusion Testing of Cryogenic Barriers. Final Report Submitted to
Scientific Ecology Group, Inc., Oak Ridge, Tenn.
Iskandar, r. K. and T. F. Jendcins. 1985. Potential uses of artificial ground freezing for contaminant
immobilization. Pp. 128-137 In Proceedings of International Conference on New Frontiers
for Hazardous Waste Management. EPA l 9-8 l 5025.
lessberger, H. L. 1980. Review, theory and application of ground freezing in civil engineering.
Cold Reg. Sci. Technol. 3:3-27.
Sayles, F. H. 1988. State of the art, Mechanical properties of frozen soil, In Frozen Ground SS, vo}
1, R. H. Jones and I. T. Holden, eds. Brookfield, Vermont: Balkema.
Shuster, I. A. 1980. Engineering quality assurance for construction ground freezing. Pp. 863-879 in
Ground Freezing, Proceedings of the 2nd International Symposium on Ground Freezing,
Trondheim, Norway, Norwegian Institute of Technology.
Sullivan, Ir., I. M. and L. A. Stefanov. 1990. Comparison of numerical simulations with
expenmental data for a prototype artificial ground freezing. Pp. 36-44 in Frozen Soil
Impacts on Agricultural, Range, and Forest Lands, K. R. Cooley, ed. Cold Regions
Research & Engineering Laboratory Spec. Rep. 90-1. Cold Regions Research &
Engineenng Laboratory, Hanover, N.H.
Sullivan, Ir., I. M., D. R. Lynch, and I. K. Iskandar. 1984. The economics of ground freezing for
management of uncontrolled hazardous waste sites. Pp. 386-392 in Proceedings of the 5th
International Conference on Management of Uncontrolled Hazardous Waste Sites.
. ~ · . ~
OCR for page 179
Representative terms from entire chapter:
frozen ground
