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

Refrigeration plant (MoreTrench) 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 Coolant Steel HDPE 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 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)

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-topics-in-ground-improvement/ground-freezing?showall=&start=8