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Artificial Ground Freezing

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Presentation on theme: "Artificial Ground Freezing"— Presentation transcript:

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

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