Artificial Ground Freezing

Report
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

similar documents