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) Smaller spacing or multiple pipe rows. LN2 Reduce hydraulic conductivity. (Klein 2012). 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
