Ground FreezingGround Freezing

Presented ByPresented By : : Muhammad HusnainMuhammad Husnain 2007-MS-GEO-162007-MS-GEO-16

ContentsContents IntroductionIntroduction Factors on which Soil freezing dependsFactors on which Soil freezing depends How Ground Freezing WorksHow Ground Freezing Works Refrigeration systemsRefrigeration systems The advantages of ground freezing The advantages of ground freezing Improved Soil PropertiesImproved Soil Properties Ground freezing for shoring andGround freezing for shoring and

groundwater cutoffgroundwater cutoff ApplicationApplication

IntroductionIntroduction Ground Freezing is adaptable to any Ground Freezing is adaptable to any

shape, size or depth required.shape, size or depth required.

It is the most effective and consistently It is the most effective and consistently reliable method of providing temporary reliable method of providing temporary support and preventing groundwater support and preventing groundwater from flowing into excavations.from flowing into excavations.

Frozen ground is nearly twice as strong Frozen ground is nearly twice as strong as concrete and is essentially as concrete and is essentially impermeable.impermeable.

The basic principle of ground freezing, which The basic principle of ground freezing, which was first used in South Wales 1862, is to was first used in South Wales 1862, is to circulate a cold medium through a suitable circulate a cold medium through a suitable pipe system, which cools the strata and thus pipe system, which cools the strata and thus converts the in-situ pore water to ice.converts the in-situ pore water to ice.

The ice is so formed bonds adjacent soil The ice is so formed bonds adjacent soil particles together and forms an particles together and forms an impermeable structure with increased impermeable structure with increased strength characteristics.strength characteristics.

Its relatively high strength can be attributed Its relatively high strength can be attributed in part to the binding together of soil in part to the binding together of soil particles with ice. particles with ice.

Introduction Contd….Introduction Contd….

When wet soil freezes, the main process is the When wet soil freezes, the main process is the physical change of soil water from liquid to solid physical change of soil water from liquid to solid that turns the soil into a hard mass resembling that turns the soil into a hard mass resembling concrete. concrete.

In a porous body like soil, water exists in a network In a porous body like soil, water exists in a network of inter-connecting pores; when it freezes, this of inter-connecting pores; when it freezes, this network becomes rigid and encloses the soil network becomes rigid and encloses the soil particles in a solid block. If the soil is dry it cannot particles in a solid block. If the soil is dry it cannot freeze.freeze.

The largest excavation in the UK, supported totally The largest excavation in the UK, supported totally by frozen ground, being 40 meters in diameter and by frozen ground, being 40 meters in diameter and 40 meters deep through unconsolidated alluvial 40 meters deep through unconsolidated alluvial deposits. deposits.

Introduction Contd….Introduction Contd….

Factors on which Soil freezing Factors on which Soil freezing dependsdepends

Factors on which soil freezing depends are :Factors on which soil freezing depends are : Its thermal properties, Its thermal properties, Moisture content Moisture content Air temperature. Air temperature. The most important is the amount of water The most important is the amount of water

to be frozen.to be frozen. The conductivity of the soil particles and The conductivity of the soil particles and

water content all influence the over-all water content all influence the over-all thermal conductivity of soil. Because clay thermal conductivity of soil. Because clay particles have a higher insulation value particles have a higher insulation value than silt or sand particles and since clay than silt or sand particles and since clay soils normally hold more moisture than silts soils normally hold more moisture than silts and sands. and sands.

Other FactorsOther Factors There are other factors that influence the depth There are other factors that influence the depth

of freezing. The insulating effect of snow of freezing. The insulating effect of snow deserves special mention. It has been shown deserves special mention. It has been shown that each foot of undisturbed snow reduces the that each foot of undisturbed snow reduces the depth of soil freezing by approximately the depth of soil freezing by approximately the same amount. Among meteorological factors same amount. Among meteorological factors such as such as

Air temperature (probably the most significant)Air temperature (probably the most significant) Sunshine Sunshine PrecipitationPrecipitation Wind velocityWind velocity

How Ground Freezing WorksHow Ground Freezing Works

There are many ways to There are many ways to freeze the ground, freeze the ground, including liquid nitrogen, including liquid nitrogen, brine, carbon dioxide.brine, carbon dioxide.

We use chilled calcium We use chilled calcium chloride brine circulating chloride brine circulating through a series of through a series of closed-ended steel pipes closed-ended steel pipes in the ground.in the ground.

The -10°F to -20°F brine circulates down The -10°F to -20°F brine circulates down along the outside pipe and up through an along the outside pipe and up through an inside pipe thus freezing the soil around the inside pipe thus freezing the soil around the pipes.pipes.

It is a completely closed and tested system It is a completely closed and tested system so that no brine goes into the ground.so that no brine goes into the ground.

The methods of ground freezing are reliable The methods of ground freezing are reliable and environmentally safe (calcium chloride and environmentally safe (calcium chloride is non-toxic and sprayed on icy roads in is non-toxic and sprayed on icy roads in many states). many states).

Frozen soil can be nearly as strong as Frozen soil can be nearly as strong as concrete and is impermeable, making it concrete and is impermeable, making it ideal for shoring and groundwater cutoff.ideal for shoring and groundwater cutoff.

How Ground Freezing Works How Ground Freezing Works Contd….Contd….

Refrigeration systemsRefrigeration systems

There are two methods of providing refrigeration There are two methods of providing refrigeration energy to freeze the ground. energy to freeze the ground.

Conventional systemConventional system Cryogenic systemsCryogenic systems

Conventional systemConventional system

The conventional system consists of a primary The conventional system consists of a primary refrigerate gas, usually ammonia, being compressed refrigerate gas, usually ammonia, being compressed and conducting its cold energy on evaporation to a and conducting its cold energy on evaporation to a secondary coolant, usually calcium chloride brine secondary coolant, usually calcium chloride brine which is circulated through the freeze tube system which is circulated through the freeze tube system to cool the strata.to cool the strata.

The refrigeration plants used for this operation are The refrigeration plants used for this operation are mounted on skid units for easy transportation.mounted on skid units for easy transportation.

In operation the ammonia does not leave the In operation the ammonia does not leave the confines of the skid unit and is protected by a series confines of the skid unit and is protected by a series of safety systems to protect against failure.of safety systems to protect against failure.

This type self contained of system can operate at This type self contained of system can operate at temperatures as low as -40 degrees Celsius and are temperatures as low as -40 degrees Celsius and are suitable for the larger projects where freezing will suitable for the larger projects where freezing will be carried on for several weeks. be carried on for several weeks.

Cryogenic systemsCryogenic systems

Where the construction Where the construction period is of short duration period is of short duration the cryogenic system is the cryogenic system is generally used.generally used.

This system uses an This system uses an expendable refrigerant expendable refrigerant usually liquid nitrogen that usually liquid nitrogen that is applied directly to the is applied directly to the freeze tubes where it freeze tubes where it evaporates at -196 c and evaporates at -196 c and the resultant gas is the resultant gas is exhausted to atmosphere.exhausted to atmosphere.

The liquid nitrogen is delivered to site by The liquid nitrogen is delivered to site by

road tankers and stored in vacuum road tankers and stored in vacuum insulated vessels of up to 100 tones insulated vessels of up to 100 tones capacity. capacity.

The system has been successfully used The system has been successfully used for example at a tunnel face beneath a for example at a tunnel face beneath a river and over 1000 meters from an river and over 1000 meters from an access shaft.access shaft.

Cryogenic systems Contd…….Cryogenic systems Contd…….

The advantages of ground freezing The advantages of ground freezing ::

Ground freezing can provide an absolute water Ground freezing can provide an absolute water cutoff and can be installed in difficult ground cutoff and can be installed in difficult ground conditions.conditions.

Ground freezing can be applied in the full range of Ground freezing can be applied in the full range of soils from clay to cobbles and boulders, in soils from clay to cobbles and boulders, in pervious or fissured rock, and filled ground.pervious or fissured rock, and filled ground.

Ground freezing is most effective as an earth Ground freezing is most effective as an earth support system where groundwater is a concern support system where groundwater is a concern and where either pumping or cutting off the water and where either pumping or cutting off the water flow cannot be readily achieved with other flow cannot be readily achieved with other methods.methods.

Since no chemical additives are used in the Since no chemical additives are used in the freeze WALL process, it has no long-term freeze WALL process, it has no long-term effect on the subsurface environment.effect on the subsurface environment.

Once the refrigeration unit is turned off and Once the refrigeration unit is turned off and the pipes abandoned, the impacted area the pipes abandoned, the impacted area gradually melts - usually restoring the gradually melts - usually restoring the groundwater and soil to their original states.groundwater and soil to their original states.

Advantages Contd….Advantages Contd….

Improved Soil PropertiesImproved Soil Properties

By ground freezing the improved soil properties are:By ground freezing the improved soil properties are:

STRENGTH :STRENGTH : Soil strength is increased many times and Soil strength is increased many times and

frequently excavations are rendered stable frequently excavations are rendered stable without any further temporary support.without any further temporary support.

Frozen soil can be likened to a weak concrete or Frozen soil can be likened to a weak concrete or rock therefore complete stability can be assured.rock therefore complete stability can be assured.

IMPERMEABILITY :IMPERMEABILITY : Impermeability is common to all frozen soil types Impermeability is common to all frozen soil types

thus the requirement for dewatering or pumping thus the requirement for dewatering or pumping is eliminated. is eliminated.

STABILITY :STABILITY :

Settlement associated with vibration during Settlement associated with vibration during piling and removal of fines due to pumping are piling and removal of fines due to pumping are eliminated. eliminated.

NON-POLLUTING :NON-POLLUTING :

Freezing does not pollute the ground water or Freezing does not pollute the ground water or affect its level in any way.affect its level in any way.

VERSATILITY:VERSATILITY:

Freezing satisfactorily stabilizes and excludes Freezing satisfactorily stabilizes and excludes ground water in all types of ground from fine ground water in all types of ground from fine micro-grain to fissured rock structures. micro-grain to fissured rock structures.

Improved Soil Properties Improved Soil Properties Contd….Contd….

Ground Freezing For Shoring AndGround Freezing For Shoring AndGroundwater CutoffGroundwater Cutoff

Shallow Excavations—Small SiShallow Excavations—Small Sitete

Shallow Excavations—Large SShallow Excavations—Large Siteite

Deep ExcavationsDeep Excavations

TunnelingTunneling Groundwater Cutoff WallGroundwater Cutoff Wall

SHALLOW EXCAVATIONSSHALLOW EXCAVATIONS

Natural Groundwater Cutoff at Shallow DepthNatural Groundwater Cutoff at Shallow Depth

Cuts off groundwater Cuts off groundwater along sides and bottom along sides and bottom to eliminate dewatering.to eliminate dewatering.

Provides stable shoring Provides stable shoring with no internal bracing with no internal bracing or struts.or struts.

Batter freeze pipe can Batter freeze pipe can be used to allow heavy be used to allow heavy construction traffic construction traffic along the top of the along the top of the wall.wall.

Bottom concrete Bottom concrete seal can usually be seal can usually be eliminated.eliminated.

Appropriate for Appropriate for excavations up to excavations up to about 40 feet deep.about 40 feet deep.

Cost-competitive Cost-competitive compared to compared to conventional conventional shoring (sheet piles, shoring (sheet piles, soldier pile walls). soldier pile walls).

SHALLOW EXCAVATIONS Contd….SHALLOW EXCAVATIONS Contd….

SHALLOW EXCAVATIONSSHALLOW EXCAVATIONS

Large SiteLarge Site

Allows large, shallow Allows large, shallow excavations to be excavations to be accomplished in the accomplished in the "dry" with no "dry" with no dewatering.dewatering.

Freeze pipes are Freeze pipes are installed nearly installed nearly horizontal using horizontal using directional drilling directional drilling methods.methods.

Completely seals the Completely seals the site from groundwater.site from groundwater.

Uplift is controlled by Uplift is controlled by freezing deeper than the freezing deeper than the planned excavation.planned excavation.

Adapts to sites of Adapts to sites of variable size and shape variable size and shape with lengths up to 1,000 with lengths up to 1,000 feet.feet.

Can also be used to cut Can also be used to cut off groundwater beneath off groundwater beneath existing structures.existing structures.

Cost effective to depths Cost effective to depths of 60 feet or more. of 60 feet or more.

SHALLOW EXCAVATIONS SHALLOW EXCAVATIONS Contd….Contd….

SHALLOW EXCAVATIONSSHALLOW EXCAVATIONSSmall SiteSmall Site

Can be designed to Can be designed to completely cut off completely cut off groundwater into the groundwater into the excavation without a natural excavation without a natural aquitard. aquitard.

Batter freeze pipe can be Batter freeze pipe can be installed at any angle to installed at any angle to accommodate site space accommodate site space constraints.constraints.

Can be modified: vertical Can be modified: vertical pipes on one side and batter pipes on one side and batter pipes on the other side.pipes on the other side.

Uplift is controlled by Uplift is controlled by freezing deeper than freezing deeper than the excavation depth.the excavation depth.

Very cost-effective Very cost-effective shoring method when shoring method when contaminated contaminated groundwater is groundwater is present.present.

Can be effectively Can be effectively used to depths of 40 used to depths of 40 feet or morefeet or more

SHALLOW EXCAVATIONS SHALLOW EXCAVATIONS Contd….Contd….

DEEP DEEP EXCAVATIONSEXCAVATIONS

DEEP EXCAVATIONSDEEP EXCAVATIONSNatural Groundwater Cutoff Near Bottom of ExcavationNatural Groundwater Cutoff Near Bottom of Excavation

Circular-shape frozen soil Circular-shape frozen soil wall provides very strong wall provides very strong shoring without internal shoring without internal bracing.bracing.

Has been used on hundreds Has been used on hundreds of shafts worldwide to of shafts worldwide to depths of 800 feet.depths of 800 feet.

Completely cuts off ground Completely cuts off ground water to eliminate water to eliminate dewatering.dewatering.

Generally costs less than Generally costs less than other deep shaft methods other deep shaft methods (secant concrete piles, jet (secant concrete piles, jet grouting, etc.).grouting, etc.).

A frozen soil seal can A frozen soil seal can be created at sites be created at sites where no natural where no natural groundwater cutoff is groundwater cutoff is present.present.

May be used in nearly May be used in nearly all soil and all soil and groundwater groundwater conditions.conditions.

Designed to resist Designed to resist uplift without uplift without expensive tie-downs. expensive tie-downs.

DEEP EXCAVATIONS Contd….DEEP EXCAVATIONS Contd….

GROUNDWATER CUTOFF WALLGROUNDWATER CUTOFF WALL

Because frozen soil has Because frozen soil has very low permeability very low permeability (less than10cm/sec) it is (less than10cm/sec) it is very effective as a very effective as a groundwater cutoff.groundwater cutoff.

A frozen soil cutoff can A frozen soil cutoff can be used to prevent be used to prevent groundwater from groundwater from entering open pit mines, entering open pit mines, gravel pits, landfills and gravel pits, landfills and other similar facilities other similar facilities that are below that are below groundwater.groundwater.

GROUNDWATER CUTOFF WALL GROUNDWATER CUTOFF WALL Contd….Contd….

Eliminates or greatly Eliminates or greatly reduces the need for reduces the need for dewatering.dewatering.

Can also be used to Can also be used to stop the migration of stop the migration of contaminated contaminated groundwater near groundwater near streams or lakes.streams or lakes.

Maintenance of a Maintenance of a buried frozen soil buried frozen soil cutoff is relatively cutoff is relatively inexpensive making it inexpensive making it competitive for long-competitive for long-term cutoffs. term cutoffs.

TUNNELINGTUNNELING

Provides stable Provides stable shoring to allow shoring to allow tunneling in wet, loose tunneling in wet, loose soils or fractured soils or fractured bedrock.bedrock.

Effective for cutting off Effective for cutting off ground water into ground water into tunnel excavation.tunnel excavation.

Frozen soil/rock can Frozen soil/rock can be used as shoring be used as shoring around unfrozen soil around unfrozen soil or the entire soil/rock or the entire soil/rock mass can be frozen.mass can be frozen.

ApplicationsApplications Bryn Mawr utility improvement projectBryn Mawr utility improvement project

One of the One of the completed projects completed projects was a frozen soil was a frozen soil shoring wall around shoring wall around a 20-foot-deep a 20-foot-deep excavation along excavation along Interstate 405 for Interstate 405 for retaining a vertical retaining a vertical cut during cut during construction of a construction of a large storm water large storm water detention vault.detention vault.

ApplicationsApplications2-Condominium in Madison Park.2-Condominium in Madison Park.

The second was a The second was a frozen soil shoring wall frozen soil shoring wall aroundaround a 10-foot deep a 10-foot deep basementbasement excavation for a excavation for a condominium located condominium located in in Madison Park just 8 Madison Park just 8 feet from Lake feet from Lake Washington.Washington.

ReferencesReferences

Geografiska Annaler, By Geografiska Annaler, By Charles HarrisCharles Harris, , (Some Factors Affecting the Rates and Processes of Periglacial Mass (Some Factors Affecting the Rates and Processes of Periglacial Mass

Movements)Movements)

http://www.bdf.co.uk/freeze.htmhttp://www.bdf.co.uk/freeze.htm http://www.cryocell.com/CivilApp.htmlhttp://www.cryocell.com/CivilApp.html http://www.djc.com/special/design98http://www.djc.com/special/design98