Artificial Ground Freezing
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Transcript Artificial Ground Freezing
Artificial Ground Freezing
Will Greenwood
Clark Green
Mike Partenio
CEE 542
Contents
1.0 Introduction
2.0 Effects on Soil and Properties
3.0 In the Field
4.0 Advantages and Disadvantages
5.0 Case Study
6.0 Current State (Info from SoilFreeze, Inc.)
7.0 Conclusions
1.0 Introduction
1.1 History
1.2 Concept
1.3 Classification
Refrigeration plant (MoreTrench)
1.1 History
1.2 Concept
Wagner and Yarmak 2012
Johanssan 2009
1.2 Concept
MoreTrench
1.3 Classification
ASTM D4083-89
2.0 Effects on Soil Properties
2.1 Hydraulic Conductivity
2.2 Strength and Stiffness
2.3 Volume Change Characteristics
2.4 Laboratory Testing
2.1 Hydraulic Conductivity
Frozen ground practically impermeable
Be aware of field limitations
Hydraulic conductivity may increase after
thawing
Concern when freezing into bedrock
2.2 Strength and Stiffness
Strength increases
Typical strengths of frozen soils (Klein 2012)
Sand:
15 MPa
Clay:
3 MPa
Frozen sands and frozen clays exhibit
similar stress-strain behavior
Stiffness increases
2.2 Strength and Stiffness
Da Re et al. 2003
2.3 Volume Change
Pore water volume increase of 9%
Soil heave
Clays may consolidate below freezing front
Thaw settlement
2.4 Laboratory Testing
Lab testing standards are documented by
both ASTM and JGS
ASTM D7300-11 – Strength of frozen soil samples under
constant strain rate
ASTM D5520-11 – Creep properties of frozen soil samples by
uniaxial compression
JGS 0171-2003 – Frost heave prediction in soils
Thermal properties always tested
2.4 Laboratory Testing
Mostly intended for natural ground freezing
Standards for triaxial testing of unfrozen soil
do not apply to frozen soil
Shear stress, triaxial compression, thaw settlement standards
still needed
3.0 In the Field
3.1 Equipment
3.2 Methods for Design
3.3 Freezing Time
3.4 Special Considerations
3.1 Equipment
Mobile Freeze Plant
Freeze Pipes
Steel
HDPE
Coolant
Typically Calcium Chloride.
Commercial coolants.
MoreTrench
3.1 Equipment
MoreTrench
Wagner and Yarmak 2012
3.2 Methods for Design
Performance approach
with contractor.
Experience needed.
Sanger and
Sayles 1979, Harris 1995
FEM
TEMP/W
Plaxis
Geo-Slope International
McCain et al. 2013
3.3 Freezing Time
Jessberger and Vyalov 1978
Sanger and Sayles 1979
3.4 Special Considerations
Groundwater velocity (< 2 m/day threshold) (Klein 2012).
Smaller spacing or multiple pipe rows.
LN2
Reduce hydraulic conductivity.
Groundwater salinity
Reduces freezing temperature and strength.
Incomplete freezing.
3.4 Special Considerations
Temperature monitoring
Thermocouples in key locations.
Soil heave and creep.
Monitor closely – be aware of adjacent structures.
4.0 Advantages
Soil applicability and versatility
Various improvement geometries
Angled freeze pipes
Cost-effective
All soil and site conditions
Freeze pipe geometry for cross
passage construction, Nanjing Metro,
China
Replaces multiple methods
Ground returns to original state
Dayong, Hui (2010)
4.0 Disadvantages
Energy intensive
Extensive monitoring
Possible failures
Uncontrolled frozen ground thickness
Damage to AGF equipment, causing leaks
Damage to nearby structures
5.0 Case Study
Dijk, P. and Bouwmeester-van
den Bos, J. (2001)
6.0 Current Conditions
Ground freezing is becoming increasingly
more common for everyday shoring projects
Currently competitive on a cost-basis
Typical cost approximately $30 – $60 per
square foot of frozen soil wall area
(SoilFreeze, Inc.)
7.0 Conclusions
Freeze soil pore water with coolant
circulation through pipes to:
Control groundwater or contaminant mobility
Increase strength and stiffness
Versatile and technique for ground
improvement
Applicable to entire soil range
Applicable to various site stratigraphy and conditions
Proper site characterization is key
Questions?
References
http://www.geoengineer.org/education/web-based-class-projects/select-topicsin-ground-improvement/ground-freezing?showall=&start=8