FOUNDATIONS WITH FROST HEAVE

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posted:: 11/25/2011
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FOUNDATIONS WITH
FROST HEAVE

By Derek Xia, M.Sc., P.Eng.,
M.CSCE, M.ASCE , M.AISC

derek.xia@ualberta.ca
Contents

 Introduction
 Soil Classification
 Freezing in Ground
 Engineering Issues
 Summary
Introduction
Introduction

 Many engineering projects are located in areas where
the ground experiences sub-zero conditions.
 Frozen ground is also caused by artificial freezing such
as chilled gas pipelines, refrigerated cold storage rooms,
and freezing ground in civil and mining engineering.
 Freezing and subsequent thaw induce engineering
problems for most projects in areas with frost condition.
 It is geotechnical engineer’s responsibility to solve most
frozen ground problems. However, it’s always good for a
civil engineer working on other areas to know some
basic issues about frozen ground.
Soil Classification
Soil Classification

Soils
Fine According to Coarse
particle size
grained soils grained soils

Silts, Clays Sands, Gravels,
Cobbles, Boulders
Soil Classification

Frost Response
Non-frost
Susceptible to Frost susceptible
soils soils
Soils
Fine According to Coarse
particle size
grained soils grained soils

Silts, Clays Sands, Gravels,
Cobbles, Boulders
Freezing in Ground
Freezing in Ground

Temperature profiles in ground

Seasonal frost Area Permafrost Area
Freezing in Ground

Phases of Un-frozen and Frozen Soils
Freezing in Ground

Unfrozen water in coarse-grained soil

Soil Grain  Most water exists in
pore as free water in
Unfrozen
water
unfrozen soil.
 Unfrozen water exists
in pore surrounding by
Ice
ice in frozen zone.
 Therefore, no path for
water migration to
frozen zone.
Freezing in Ground

Freezing in coarse-grained soils

 Most pore water freezes in frozen zone as frost penetrates
into soil.
 Pore water expands by ~9% volumetrically when freezing.
 This 9% expansion usually pushes the water downward
into the unfrozen zone and drains away.
 Normally, it does NOT change the soil structure. No frost
heave takes place in these soils.
Freezing in Ground

Unfrozen water in fine-grained soil

 Water in fine-grained soil exists simultaneously as
 free water in bulk,
 capillary water,
 film water,
 and hygroscopic water.
 Each has different freezing point due to different stresses.
 Water coexists with ice as thin films in frozen soil through which
moisture migration may occur.
Freezing in Ground

Unfrozen water in fine-grained soil
Freezing in Ground – Zones in Frozen Soil
Freezing in Ground

Freezing in fine-grained soils
 Freezing of a fine-grained soil is a very
complicated process including both mass and
heat transfer.
 Ice crystals initiate in frozen zone with frost
penetrating into a fine-grained soil.
 While frost penetrates into soil, water is drawn
from the unfrozen zone towards the ice crystals
through the frozen fringe, forming ice lenses.
 The warmest ice lens grows until the next ice lens
forming during transient heat flow.
Frozen
Fringe
 Final ice lens can grow forever during the thermal
steady state if there is enough water supply.
Freezing in Ground – Transient Freezing
Top plate: -5oC, Bottom plate 2oC

02h19
Freezing in Ground – Transient Freezing
Top plate: -5oC, Bottom plate 2oC

02h36
Freezing in Ground – Transient Freezing
Top plate: -5oC, Bottom plate 2oC

02h52
Freezing in Ground – Transient Freezing
Top plate: -5oC, Bottom plate 2oC

03h08
Freezing in Ground – Transient Freezing
Top plate: -5oC, Bottom plate 2oC

03h24
Freezing in Ground – Transient Freezing
Top plate: -5oC, Bottom plate 2oC

03h40
Freezing in Ground – Transient Freezing
Top plate: -5oC, Bottom plate 2oC

03h56
Freezing in Ground – Transient Freezing
Top plate: -5oC, Bottom plate 2oC

04h12
Freezing in Ground – Transient Freezing
Top plate: -5oC, Bottom plate 2oC

04h28
Freezing in Ground – Steady State
Top plate: -5oC, Bottom plate 2oC

21h45
Freezing in Ground – Steady State
Top plate: -5oC, Bottom plate 2oC

32h00
Freezing in Ground – Steady State
Top plate: -5oC, Bottom plate 2oC

42h00
Freezing in Ground – Steady State
Top plate: -5oC, Bottom plate 2oC

52h00
Freezing in Ground – Steady State
Top plate: -5oC, Bottom plate 2oC

62h00
Freezing in Ground – Steady State
Top plate: -5oC, Bottom plate 2oC

72h00
Freezing in Ground – Steady State
Top plate: -5oC, Bottom plate 2oC

82h00
Freezing in Ground – Frozen Soil Structure
Frozen Soil (fine) MC redistribution

Frozen zone
No visible ice lens

Final ice lens
Vertical ice lens
Frozen fringe
Frost front

Unfrozen zone
Freezing in Ground – Frost Penetration

130
120
110
Height of sample (mm)

100
90 Frost front
80 Latest Ice lens
Last ice Lens
70
60
50
40
30
0 5 10 15 20 25 30 35
Time (hour)
Freezing in Ground – Final Ice Lens Growth

0.8

0.7

0.6
Thickness (mm)

0.5

0.4

0.3

0.2

0.1

0.0
20 25 30 35 40 45 50 55 60 65 70 75 80 85
Time (hour)
Engineering Issues
Engineering Issues

Saturated fine Uplifts and Bearing
grained soil Frost-jacking Capacities

Freezing Engineering Settlements
Problems
Frost heave
Stabilities
Others
Thaw
Engineering Issues

Shallow Foundation
 In Ft. McMurray, Alberta the typical
amount of frost heave is 50-75mm.
 Uplift force due to frost heave can be
up to 2MPa if the heave is confined.
 Burying the foundation below the frost
depth (approximately 4m in Ft. Mc.) is
a normal approach.
 This approach can also solve the
problem due to thaw weakening and
extensive settlement.
Engineering Issues

Shallow Foundation for Heated Buildings
Exterior Heated building
interior

 Shallow foundations for heated
buildings need to be insulated to
eliminate frost penetrating below the
foundations.
 Therefore, avoid frost heave.
Engineering Issues

Uplift force through voidform on piles
 Uplift force due to frost heave can be
up to 2MPa if the heave is confined.
 Voidform, an expanded polystyrene
product, should be used to allow this
upward movement.
 For a known thickness of voidform and
a predicted amount of frost heave, the
uplift pressure on the bottom of the
pile cap can be calculated.
Engineering Issues

Adfreeze forces on piles
 Adfreeze is a bond of frozen
moisture between the foundation
sides and the soil.
 The value of adfreeze is typically
55-140kPa.
 Using bond breakers can
eliminate the adfreeze forces
around the cap.
 Adfreeze forces can induce frost
jacking on a pile.
Engineering Issues

Frost Jacking
 Frost jacking occurs
when a pile is not
embedded well.
 Pile goes up with frozen
soil during winters.
 Soil settles down during
summers when thawing
 The pile can be jacked
out of the ground after
several cycles.
Engineering Issues

Frost Jacking
 Frost jacking occurs
when a pile is not
embedded well.
 Pile goes up with frozen
soil during winters.
 Soil settles down during
summers when thawing.
 The pile can be jacked
out of the ground after
several cycles.
Engineering Issues

Permafrost area

 Frozen soil is very strong material.
 Embed piles into permafrost and
elevate structures above the grade to
minimize heat transfer into soil.

Active layer
 Allow convection between structure
and grade to cool down the piles.
Permafrost
 Key issue is to avoid thawing
permafrost to preserve its strength.
Summary

Frost Heave Requires
 Freezing temperatures (temperature gradient) for a prolonged period of
time.
 Fine grained soil particles allowing ice lenses initiation and moisture
migration.
 Water supply.

Engineering Issues
 Frost heave and subsequent thaw weakening and settlement.
 Uplift forces through voidform and adfreezing.
 Frost-jacking.
 Engineering in permafrost.