12 2.3 Volume Change Pore water volume increase of 9% Soil heave Clays may consolidate below freezing frontThaw settlement
13 2.4 Laboratory TestingLab testing standards are documented by both ASTM and JGSASTM D – Strength of frozen soil samples under constant strain rateASTM D – Creep properties of frozen soil samples by uniaxial compressionJGS – Frost heave prediction in soilsThermal 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 soilShear 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 Time3.4 Special Considerations
16 3.1 Equipment Mobile Freeze Plant Freeze Pipes Coolant Steel HDPE Typically Calcium Chloride.Commercial coolants.MoreTrench
18 3.2 Methods for DesignPerformance approach with contractor. Experience needed.Sanger andSayles 1979, Harris 1995FEMTEMP/WPlaxisGeo-Slope InternationalMcCain et al. 2013
19 3.3 Freezing TimeJessberger and Vyalov 1978Sanger and Sayles 1979
20 3.4 Special Considerations Groundwater velocity (< 2 m/day threshold) (Klein 2012).Smaller spacing or multiple pipe rows.LN2Reduce hydraulic conductivity.Groundwater salinityReduces freezing temperature and strength.Incomplete freezing.
21 3.4 Special Considerations Temperature monitoringThermocouples 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 conditionsVarious improvement geometriesAngled freeze pipesCost-effectiveReplaces multiple methodsGround returns to original stateFreeze pipe geometry for cross passage construction, Nanjing Metro, ChinaDayong, Hui (2010)
23 4.0 Disadvantages Energy intensive Extensive monitoring Possible failuresUncontrolled frozen ground thicknessDamage to AGF equipment, causing leaksDamage to nearby structures
24 5.0 Case StudyDijk, P. and Bouwmeester-van den Bos, J. (2001)
25 6.0 Current ConditionsGround freezing is becoming increasingly more common for everyday shoring projectsCurrently competitive on a cost-basisTypical cost approximately $30 – $60 per square foot of frozen soil wall area (SoilFreeze, Inc.)
26 7.0 ConclusionsFreeze soil pore water with coolant circulation through pipes to:Control groundwater or contaminant mobilityIncrease strength and stiffnessVersatile and technique for ground improvementApplicable to entire soil rangeApplicable to various site stratigraphy and conditionsProper site characterization is key