GROUND FREEZING FOR SUPPORT OF EXCAVATION & GROUNDWATER CUTOFF 9/25/2018 - APWA-WA
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9/25/2018
GROUND FREEZING FOR SUPPORT OF
EXCAVATION & GROUNDWATER CUTOFF
BRENTON R COOK, PE – SOILFREEZE, INC.
1
9/25/2018
WHAT IS GROUND FREEZING AND
HOW DOES IT WORK?
www.soilfreeze.com
WHAT IS GROUND FREEZING AND
HOW DOES IT WORK?
FROZEN SOIL AT A GLANCE
In-situ porewater is artificially frozen.
The ice within the soil matrix bonds the solids
forming a concrete-like mass.
The frozen soil mass provides structure and a
waterproof barrier.
Saturated and unsaturated soils can be frozen,
however, some moisture within the soil is required.
Porewater / Ice
Soil Particles
www.soilfreeze.com
2
9/25/2018
WHAT IS GROUND FREEZING AND
HOW DOES IT WORK?
HOW COMPETENT IS FROZEN GROUND?
www.soilfreeze.com
WHAT IS GROUND FREEZING AND
HOW DOES IT WORK?
MODULAR CHIILLER SYSTEM – MOST COMMON APPROACH
Chillers extract heat from brine circulating through manifold via vapor-
compression refrigeration cycle
MODULAR AIR COOLED CHILLER UNITS
CHILLED BRINE
PUMP MANIFOLD
FREEZE PIPES
www.soilfreeze.com
3
9/25/2018
WHAT IS GROUND FREEZING AND
HOW DOES IT WORK?
MODULAR CHIILLER SYSTEM – ENERGY TRANSFER DIAGRAM
HEAT RELEASED TO AMBIENT AIR
3 2
CONDENSOR R-507 REFRIG.
PRIMARY
EXPANSION COMPRESSOR COOLANT
VALVE CYCLE
EVAPORATOR BARREL
4 1
CALCIUM CHORIDE BRINE
PUMP
SECONDARY
COOLANT
FREEZE PIPES CYCLE
HEAT LOADS FROM GROUND www.soilfreeze.com
WHAT IS GROUND FREEZING AND
HOW DOES IT WORK?
PRIMARY COOLANT – R-507 REFRIGERANT
Fully contained within modular chiller units
Common refrigerant for air conditioning applications
EPA regulated
www.soilfreeze.com
4
9/25/2018
WHAT IS GROUND FREEZING AND
HOW DOES IT WORK?
SECONDARY COOLANT – CALCIUM CHLORIDE BRINE (30% SOLUTION)
Fully contained within freeze system manifold
Freezes at -60°F
Non toxic & environmentally
benign
Also used as de-icer on roads
www.soilfreeze.com
WHAT IS GROUND FREEZING AND
HOW DOES IT WORK?
LIQUID NITROGEN FREEZE SYSTEM – LESS COMMON APPROACH
LN2 is trucked to the site and dripped into freeze pipes
(Modified after van Dorst 2013)
www.soilfreeze.com
5
9/25/2018
WHAT IS GROUND FREEZING AND
HOW DOES IT WORK?
FORMATION OF FROZEN SOILS – PLAN SECTION
www.soilfreeze.com
WHAT IS GROUND FREEZING AND
HOW DOES IT WORK?
STANDARD FROZEN SOIL WALL ILLUSTRATION
FREEZE PIPES
GROUNDWATER
FROZEN SOIL
LOW PERMEABILITY SOIL LAYER
www.soilfreeze.com
6
9/25/2018
WHAT IS GROUND FREEZING AND
HOW DOES IT WORK?
COMMON MISCONCEPTIONS
Nothing is injected into the ground
“Are the chemicals that you pump into the ground toxic?”
Climate is a system design consideration, not a hindrance
“Daytime temperatures push 100 degrees here. Freezing? You nuts?!”
Frost heave is not a universal certainty
“I dunno man… I’ve been to Alaska and seen permafrost first hand. I’m not
looking to increase the elevation of my jobsite.”
Time required to form frozen soils can vary
“My schedule says that it would take exactly 21 days to form the frozen soil. Now
you’re telling me it’s going to take 23 days? How can I trust you going forward?”
www.soilfreeze.com
APPLICATIONS
www.soilfreeze.com
7
9/25/2018
APPLICATIONS
GROUNDWATER CUTOFF
Large civil projects with complex existing infrastructure
www.soilfreeze.com
APPLICATIONS
SITE REMEDIATION
Superfund sites
Contaminated soils, wood debris, etc.
www.soilfreeze.com
8
9/25/2018
APPLICATIONS
TEMPORARY SHORING
Building and shaft excavations
Lift station / wet well excavations
Repair of sensitive infrastructure
www.soilfreeze.com
APPLICATIONS
TUNNELING
Twin tunnel cross passage construction
TBM break-out and break-in portal stabilization
TBM safe havens
www.soilfreeze.com
9
9/25/2018
APPLICATIONS
TEMPORARY GROUND IMPROVEMENT
Railroad embankment stabilization for pipe or box jacking
www.soilfreeze.com
ADVANTAGES
www.soilfreeze.com
109/25/2018
ADVANTAGES
IMPERMEABLE BARRIER
Greatly reduce (or eliminate) dewatering and water treatment efforts
www.soilfreeze.com
ADVANTAGES
VERY ADAPTABLE
Effective in all soil types to any depth
Freeze systems can take nearly any
shape – horizontal or vertical installs
Easily installed – tight areas, low
overhead, minimal vibrations
www.soilfreeze.com
119/25/2018
ADVANTAGES
FREEZE PIPES CAN BE DRILLED OR DRIVEN INTO PLACE
Driven Installations
• Installation depths typically < 50 ft
• Rapid production rate – up to 60 freeze pipes per day
• Small man operated hammers for confined spaces
Drilled Installations
• Can install through any soil or rock
• Not limited by install depth
• Slower production rate
• Better positioning accuracy
www.soilfreeze.com
ADVANTAGES
DRIVEN FREEZE PIPE INSTALLATIONS
PIN-PILE RIG
HAND OPERATED
PNEUMATIC HAMMER
www.soilfreeze.com
129/25/2018
ADVANTAGES
DRILLED FREEZE PIPE INSTALLATIONS
SONIC DUAL-ROTARY
FLIGHTED AUGER
www.soilfreeze.com
ADVANTAGES
VERIFIABLE
Temperature sensors and piezometers are used to verify the extent of freezing
before excavations begin.
www.soilfreeze.com
139/25/2018
ADVANTAGES
ENVIRONMENTALLY FRIENDLY
Temporary – system can be completely removed upon completion of work
and ground will return to its original state
Equipment is electric
Freeze process is fully contained – no chemicals injected into ground!
www.soilfreeze.com
CONSIDERATIONS
www.soilfreeze.com
149/25/2018
CONSIDERATIONS
TIME TO FORM FROZEN SOILS
Time required to form frozen soils, or ‘freezedown period’, is dictated by:
1. Soil type
2. Groundwater movement
3. Groundwater salinity
4. Design requirements – shoring & groundwater cutoff or groundwater cutoff only?
5. Freeze pipe spacings
6. Means and methods of freezing
Freezedown times typically vary anywhere between 3 to 8 weeks.
…while liquid nitrogen requires only 2 to 4 days.
www.soilfreeze.com
CONSIDERATIONS
GROUNDWATER MOVEMENT
Most common (and important!) design consideration
General rule of thumb:
Darcy groundwater velocities > 5 feet per day tend to create issues
Typical impact to ground freezing – increased freezedown duration
Worst case – freeze propagation through soils is completely inhibited
WHEN DO WE START? I’LL NEED TO DISCUSS
WITH MY ENGINEERS…
www.soilfreeze.com
159/25/2018
CONSIDERATIONS
GROUNDWATER MOVEMENT
Cyclical (tidal) groundwater movement is okay!
www.soilfreeze.com
CONSIDERATIONS
STRATIGRAPHY
Are there low permeability layers at depth?
www.soilfreeze.com
169/25/2018
CONSIDERATIONS
BRACKISH GROUNDWATER OR PRESENCE OF CONTAMINANTS
Generally reduces frozen soil strengths
Can result in a moderate increase freezedown duration
Typically not a problem, but needs to be incorporated into design
www.soilfreeze.com
CONSIDERATIONS
EXISTING INFRASTRUCTURE SENSITIVE TO FREEZING
Static water lines – hydrant laterals
Storm or sewer lines at full capacity with static effluent – not as common
www.soilfreeze.com
179/25/2018
CONSIDERATIONS
HEAVE SUSCEPTIBLE SOILS
Two categories of frost heave: Primary and Secondary
Frost heave is generally a misunderstood process
To be revisited later in this presentation
www.soilfreeze.com
CONSIDERATIONS
AVAILABILITY OF ELECTRICAL POWER
Urban sites – line power
Rural or remote sites – diesel generator
Standard calcium chloride chiller system requires 460 volt, 3-phase power
Liquid nitrogen systems – no power necessary!
www.soilfreeze.com
189/25/2018
GROUND FREEZING
CONCEPTS
www.soilfreeze.com
GROUND FREEZING CONCEPTS
FROZEN SOIL GRAVITY WALL SHORING
For continuous wall applications
www.soilfreeze.com
199/25/2018
GROUND FREEZING CONCEPTS
FROZEN SOIL SHORING WITH TIEBACK OR SOIL NAILS
Continuous walls exceeding 20 feet in height
Tiebacks & soils nails to be installed above groundwater table
www.soilfreeze.com
GROUND FREEZING CONCEPTS
SYSTEMS IN COMPRESSION – SHAFTS
Not limited by excavation depth
Shafts can be elliptical in shape
www.soilfreeze.com
209/25/2018
GROUND FREEZING CONCEPTS
SYSTEMS IN COMPRESSION – HORIZONTAL SHORING
www.soilfreeze.com
GROUND FREEZING CONCEPTS
ZONE FREEZE PIPES
How to control groundwater coming up from the base of excavation?
To plug or not to plug…
Shaft Without Zone Freezing Shaft With Zone Freezing
www.soilfreeze.com
219/25/2018
GROUND FREEZING CONCEPTS
HOW DO ZONE FREEZE PIPES WORK?
www.soilfreeze.com
GROUND FREEZING CONCEPTS
WHY USE ZONE FREEZE PIPES?
Forms structural & impermeable excavation base
Limits freezing in areas where it is not required
Reduces chilling capacity, therefore, reduces energy consumption
Plastic / HDPE insulated zone can be easily excavated
www.soilfreeze.com
229/25/2018
GROUND FREEZING CONCEPTS
WET WELL EXCAVATION NOT REQUIRING ZONE FREEZE PIPES
www.soilfreeze.com
GROUND FREEZING CONCEPTS
WET WELL EXCAVATION NOT REQUIRING ZONE FREEZE PIPES
www.soilfreeze.com
239/25/2018
GROUND FREEZING CONCEPTS
WET WELL EXCAVATION REQUIRING ZONE FREEZE PIPES
www.soilfreeze.com
GROUND FREEZING CONCEPTS
WET WELL EXCAVATION REQUIRING ZONE FREEZE PIPES
www.soilfreeze.com
249/25/2018
ENGINEERING
FROZEN GROUND
www.soilfreeze.com
ENGINEERING FROZEN GROUND
TYPICALLY CONTRACTOR DESIGNED
Contractor means and methods often drive design
There are a few consulting firms in the United States with expertise in ground
freezing
In the end, contractor often ends up the engineer of record
www.soilfreeze.com
259/25/2018
ENGINEERING FROZEN GROUND
MODELING
ITERATIVE
Coupled Thermal & Seepage Models Geotechnical Constitutive Models
2D finite element method Typically only for shoring
Simulate frozen soil applications
propagation with time Simulate strength and
Assess impacts of deformation performance
groundwater flow 2D or 3D finite element
Calculate heat loads for methods
chiller sizing
www.soilfreeze.com
ENGINEERING FROZEN GROUND
THERMAL PARAMETERS FOR DESIGN
Unfrozen / Frozen Thermal Conductivities
• Published data
• Lab testing
Unfrozen / Frozen Heat Capacity
• Published data
• Lab testing
Unfrozen Volumetric Water Content
• Standard geotech. lab testing
Unfrozen Unit Weight / Density
• Standard geotech. lab testing
Fines Content
• Standard geotech. lab testing
Hey geotechs! We actually look at those moisture contents!
www.soilfreeze.com
269/25/2018
ENGINEERING FROZEN GROUND
CONSTITUTIVE PARAMETERS FOR DESIGN
Frozen Strengths & Stiffnesses
• Frozen soils laboratory tests
• Published data & correlations
Creep & Unsaturated Strength Reductions
• Standard geotech. lab testing
• Frozen soils laboratory tests
• Published data & correlations
• Experience
www.soilfreeze.com
ENGINEERING FROZEN GROUND
SEEPAGE PARAMETERS FOR DESIGN
Groundwater Gradients
• Boring logs
• Monitoring well levels
• Groundwater maps
Coefficient of Permeability
• Geotech. lab testing
• Correlations
Darcy Groundwater Velocity… Not Seepage Velocity
• Calculated using groundwater gradient and coeff. of permeability
www.soilfreeze.com
279/25/2018
ENGINEERING FROZEN GROUND
FROZEN SOILS LABORATORY TESTING
Not commonly performed – $$ CAN BE PRICEY $$
Published data, correlations, and designer experience usually sufficient
For projects with extreme loading and/or stringent design constraints
Only a handful of laboratories that have capability and expertise
TRIAXIAL HEAVE SUSCEPTIBILITY CONSTANT STRAIN UNIAXIAL / CREEP
[NOT STANDARDIZED] [ASTM D5918-13] [ASTM D7300-11 & D5520-11]
www.soilfreeze.com
ENGINEERING FROZEN GROUND
FROZEN SOILS TRIAXIAL TESTING [SOON TO BE STANDARDIZED]
Frozen soil cohesion
Friction angle
Stiffnesses
Performed at minimum of two different
temperatures; -20°C and -10°C
www.soilfreeze.com
289/25/2018
ENGINEERING FROZEN GROUND
FROZEN SOILS UNIAXIAL COMPRESSION UNDER CONSTANT
STRAIN RATE [ASTM D7300-11]
Unconfined compressive strength ‘qu’
Stiffness
Performed at minimum of two different
temperatures; -20°C and -10°C
www.soilfreeze.com
ENGINEERING FROZEN GROUND
FROZEN SOILS UNIAXIAL CREEP UNDER CONSTANT APPLIED
LOAD [ASTM D5520-11]
90% qu
Apply constant loads at various
fractions of the unconfined compressive 75% qu
strength ‘qu’
Measure creep reductions of qu versus
time
25% qu
www.soilfreeze.com
299/25/2018
ENGINEERING FROZEN GROUND
FROST HEAVE AND THAW WEAKENING SUSCEPTIBILITY
[ASTM D5918-13]
Measures relative susceptibility to secondary frost heave under various
confining stress conditions
Segregation potential of soil can also be measured
• Ratio of pore water intake velocity to temperature gradient across the
frozen fringe
(ASTM 2018)
www.soilfreeze.com
ENGINEERING FROZEN GROUND
HEAVE ASSESSMENT
Primary ‘In-situ’ Heave
• Liquid to ice phase change – 9% volumetric expansion ‘pure water’
… But soil is a combination of water, air, and solids
• Function of saturation ‘S’, porosity ‘n’, and soil type
Simplistic estimation:
Primary Heave = 0.09*S*n
Gravels: 0% to 2%
Sands: 0% to 3%
Silts & Clays: 0.5% to 5%
Primary heave either occurs or it doesn’t and there’s not much that can be
done to prevent it.
www.soilfreeze.com
309/25/2018
ENGINEERING FROZEN GROUND
HEAVE ASSESSMENT
Secondary ‘Segregational’ Heave
• Most pronounced frost heave mechanism
• Capillary action and cryogenic suction draws porewater to frost boundary
• Ice lens formation causes soil structure to segregate near frost front
• A number of elements influence secondary heave:
1) Presence of water source
2) Confining pressure
3) Soil type
4) Clay fraction
5) Temperature gradient
If subsurface soils are susceptible,
secondary frost heave should be a
design consideration for long
duration freeze systems.
www.soilfreeze.com
SYSTEM CONSTRUCTION
& OPERATION
www.soilfreeze.com
319/25/2018
SYSTEM CONSTRUCTION & OPERATION
LAYOUT FREEZE PIPES AND LOCATE UTILITIES
www.soilfreeze.com
SYSTEM CONSTRUCTION & OPERATION
INSTALL FREEZE PIPES
www.soilfreeze.com
329/25/2018
SYSTEM CONSTRUCTION & OPERATION
PRESSURE TEST INDIVIDUAL FREEZE PIPES
www.soilfreeze.com
SYSTEM CONSTRUCTION & OPERATION
FREEZE PIPE AS-BUILT SURVEYS
www.soilfreeze.com
339/25/2018
SYSTEM CONSTRUCTION & OPERATION
FREEZE SYSTEM DESIGN
Systems are modeled using dynamic fluid simulations
• Identify system pressures
• Size pump(s)
• Evenly distribute chilled calcium chloride brine through freeze pipes
www.soilfreeze.com
SYSTEM CONSTRUCTION & OPERATION
MANIFOLD AND HEAD HOSE ASSEMBLY
www.soilfreeze.com
349/25/2018
SYSTEM CONSTRUCTION & OPERATION
CHILLER PLANT ASSEMBLY
www.soilfreeze.com
SYSTEM CONSTRUCTION & OPERATION
www.soilfreeze.com
359/25/2018
SYSTEM CONSTRUCTION & OPERATION
INSTALL GROUND TEMPERATURE INSTRUMENTATION
www.soilfreeze.com
SYSTEM CONSTRUCTION & OPERATION
INSTALL GROUNDWATER MONITORING INSTRUMENTATION
Pressure Sensor
www.soilfreeze.com
369/25/2018
SYSTEM CONSTRUCTION & OPERATION
ACTIVATE CHILLER PLANT – BEGIN FREEZEDOWN
www.soilfreeze.com
SYSTEM CONSTRUCTION & OPERATION
MONITOR FREEZING – DEVELOP AS-BUILT THERMAL MODELS
www.soilfreeze.com
379/25/2018
SYSTEM CONSTRUCTION & OPERATION
MONITOR FREEZING – DEVELOP AS-BUILT THERMAL MODELS
www.soilfreeze.com
SYSTEM CONSTRUCTION & OPERATION
MONITOR FREEZING – GROUNDWATER LEVELS
www.soilfreeze.com
389/25/2018
SYSTEM CONSTRUCTION & OPERATION
EXCAVATION
www.soilfreeze.com
SYSTEM CONSTRUCTION & OPERATION
FREEZE PIPE REMOVAL (OPTIONAL)
www.soilfreeze.com
399/25/2018
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