1. Artificial Ground Freezing
Will Greenwood
Clark Green
Mike Partenio
CEE 542

2. 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

3. Refrigeration plant (MoreTrench)
1.0 Introduction
1.1 History
1.2 Concept
1.3 Classification
Refrigeration plant (MoreTrench)

4. 1.1 History

5. 1.2 Concept
Wagner and Yarmak 2012
Johanssan 2009

6. 1.2 Concept
MoreTrench

7. 1.3 Classification
ASTM D

8. 2.0 Effects on Soil Properties
2.1 Hydraulic Conductivity
2.2 Strength and Stiffness
2.3 Volume Change Characteristics
2.4 Laboratory Testing

9. 2.1 Hydraulic Conductivity
Frozen ground practically impermeable
Be aware of field limitations
Hydraulic conductivity may increase after thawing
Concern when freezing into bedrock

10. 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

11. 2.2 Strength and Stiffness
Da Re et al. 2003

12. 2.3 Volume Change Pore water volume increase of 9% Soil heave
Clays may consolidate below freezing front
Thaw settlement

13. 2.4 Laboratory Testing
Lab testing standards are documented by both ASTM and JGS
ASTM D – Strength of frozen soil samples under constant strain rate
ASTM D – Creep properties of frozen soil samples by uniaxial compression
JGS – Frost heave prediction in soils
Thermal properties always tested

14. 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

15. 3.0 In the Field 3.1 Equipment 3.2 Methods for Design
3.3 Freezing Time
3.4 Special Considerations

16. 3.1 Equipment Mobile Freeze Plant Freeze Pipes Coolant Steel HDPE
Typically Calcium Chloride.
Commercial coolants.
MoreTrench

17. 3.1 Equipment
MoreTrench
Wagner and Yarmak 2012

18. 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

19. 3.3 Freezing Time
Jessberger and Vyalov 1978
Sanger and Sayles 1979

20. 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.

21. 3.4 Special Considerations
Temperature monitoring
Thermocouples in key locations.
Soil heave and creep.
Monitor closely – be aware of adjacent structures.

22. 4.0 Advantages Soil applicability and versatility
All soil and site conditions
Various improvement geometries
Angled freeze pipes
Cost-effective
Replaces multiple methods
Ground returns to original state
Freeze pipe geometry for cross passage construction, Nanjing Metro, China
Dayong, Hui (2010)

23. 4.0 Disadvantages Energy intensive Extensive monitoring
Possible failures
Uncontrolled frozen ground thickness
Damage to AGF equipment, causing leaks
Damage to nearby structures

24. 5.0 Case Study
Dijk, P. and Bouwmeester-van den Bos, J. (2001)

25. 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.)

26. 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

27. Questions?

28. References