FOUNDATIONS WITH FROST HEAVE by HC111126052617

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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


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


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


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


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


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


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


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


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


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.

								
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