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FOUNDATIONS WITH FROST HEAVE

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.

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FOUNDATIONS WITH FROST HEAVE

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  1. FOUNDATIONS WITH FROST HEAVE By Derek Xia, M.Sc., P.Eng., M.CSCE, M.ASCE , M.AISC derek.xia@ualberta.ca

  2. Contents • Introduction • Soil Classification • Freezing in Ground • Engineering Issues • Summary

  3. Introduction

  4. 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.

  5. Soil Classification

  6. Soil Classification Soils Finegrained soils Coarse grained soils According to particle size Silts, Clays Sands, Gravels, Cobbles, Boulders

  7. Soil Classification Frost Susceptible soils Non-frost susceptible soils Response to Frost Soils Finegrained soils Coarse grained soils According to particle size Silts, Clays Sands, Gravels, Cobbles, Boulders

  8. Freezing in Ground

  9. Freezing in Ground Temperature profiles in ground Seasonal frost Area Permafrost Area

  10. Freezing in Ground Phases of Un-frozen and Frozen Soils

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

  12. 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.

  13. 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.

  14. Freezing in Ground Unfrozen water in fine-grained soil

  15. Freezing in Ground – Zones in Frozen Soil

  16. 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. • Final ice lens can grow forever during the thermal steady state if there is enough water supply. Frozen Fringe

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

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

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

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

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

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

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

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

  25. Freezing in Ground – Transient Freezing Top plate: -5oC, Bottom plate 2oC 04h28

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

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

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

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

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

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

  32. Freezing in Ground – Steady State Top plate: -5oC, Bottom plate 2oC 82h00

  33. Frozen zoneNo visible ice lens Final ice lens Vertical ice lens Frozen fringe Frost front Unfrozen zone Freezing in Ground – Frozen Soil Structure Frozen Soil (fine) MC redistribution

  34. Latest Ice Lens Freezing in Ground – Frost Penetration

  35. Freezing in Ground – Final Ice Lens Growth

  36. Engineering Issues

  37. Engineering Issues Saturated fine grained soil Uplifts and Frost-jacking Bearing Capacities Freezing Engineering Problems Settlements Frost heave Stabilities Others Thaw

  38. 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.

  39. Engineering Issues Shallow Foundation for Heated Buildings • Shallow foundations for heated buildings need to be insulated to eliminate frost penetrating below the foundations. • Therefore, avoid frost heave. Heated building interior Exterior

  40. 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.

  41. 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.

  42. 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.

  43. 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.

  44. 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.

  45. 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.

  46. 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.

  47. 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.

  48. 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.

  49. 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.

  50. 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.

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