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Builder’s Technical Session

Foundation Movements and Heave in Basements Presented by : Charles Kwok, M.Sc., P.Eng . Stantec (Jacques Whitford) Presented in Partnership with:. Builder’s Technical Session. Session Overview. Section I: Soil Basics Section IIa: Heaving  Frost

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Builder’s Technical Session

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  1. Foundation Movements and Heave in Basements Presented by: Charles Kwok, M.Sc., P.Eng. Stantec (Jacques Whitford) Presented in Partnership with: Builder’s Technical Session

  2. Session Overview • Section I: Soil Basics • Section IIa: Heaving  Frost • Section IIb: Heaving  Swell (and Settlement  Shrink)

  3. SECTION ISOIL BASICS

  4. Phase Diagram Air Water Soil Particles 3 Components in a Soil Matrix:

  5. Soil Types and Permeability Less permeable More permeable Clay Silt Sand Gravel

  6. SECTION IIaHEAVING: FROST

  7. Frost Related Problems Conditions for Frost Heave to occur: • Freezing Temperatures • Water • Frost susceptible soils (fine grained soils and fine sand)

  8. Frost Heave – what happens? Soil

  9. Frost Heave Ice Lenses Soil

  10. Frost Heave • Water expands 9% in volume when it changes to ice • Formation of ice lenses Soil Ice Lenses

  11. Frost Heave Soil Ice Lenses

  12. Frost Related Problems Heaving of entire foundation

  13. Frost Penetration varies from 1.5 m to over 3.5 m in Alberta • Typical Frost Penetration • Fort McMurray = 3.2 m • Edmonton = 2.3 m • Red Deer = 2.3 m • Calgary = 2.0 m • Lethbridge = 1.7 m

  14. Frost Jacking of Fence Posts

  15. Case Study: #1Winter Construction/Frost Penetration Causes of foundation movement due to freezing: • Insufficient protection of footings and foundations during construction from water accumulation and freezing temperature. • Insufficient protection from frost penetration after construction

  16. Exposure during construction…

  17. Water in excavation…

  18. Footing hoarded, not heated…

  19. Frozen backfill…

  20. Diagram of What Happened

  21. Remediation: Lift the House

  22. Resulting damage: cracking

  23. …separation along floor slab …

  24. …baseboard separation, door frame alignment…

  25. Frozen backfill beneath slab…

  26. Winter Construction Best Practice • Keep water out of the excavation • Prevent base of excavation from freezing • Prevent foundation bearing surfaces from freezing • Recognize the issues with frozen backfill material

  27. Frost Penetration Protection Measures Protect Against Frost With: • Soil cover (greater than frost penetration) • Rigid insulation (equivalent to soil cover) Protect the Garage Floor by: • Removing frost susceptible materials from under the garage floor • Insulating the garage floor • Heating the garage

  28. SECTION IIbHEAVING: SWELL(and Settlement: Shrink)

  29. Soil Swelling and Shrinking Swelling / shrinking potential exists if: • Clays (can be either medium or high plastic) • Water content change in soil beneath foundations (post construction) • Expansion/heave - increased water content • Shrinking/settlement - decreased water content

  30. Identifying Expansive Soils • Should be identified by lab testing during geotechnical investigation (very difficult to identify during construction, i.e. visually) • Extremely important to obtain and read geotechnical report • Special requirements for foundations in areas of expansive/shrinking soils

  31. Case Study #2: Swelling Soil • Cause: water is not drained at the footing level and permitted to penetrate subgrade • Increased water content causes the soil to swell • Swelling exerts pressure on footings, telepost pads and/or the concrete basement slab and raises them

  32. Case Study #2: Swelling Soil • Poor quality backfill permitted water to penetrate adjacent to the foundation • Increased water content of soils beneath exterior footings caused heaving • Interior footings remained stationary and caused separation between interior walls and ceilings/floors

  33. Negative slope (i.e. toward house)

  34. Negative slope (i.e. toward house)

  35. Pour Quality Backfill Drywall Bearing Wall Concrete Basement floor Case Study #2: Swelling Soil Pour Quality Backfill

  36. Damages: crack between the house and patio wall…

  37. … drywall buckling…

  38. … cracking of stipple ceiling…

  39. … separation of tile at tub…

  40. Proper Exterior Backfilling to Prevent Heaving • Proper grading • Timely grading (Prior to winter; first thing in spring) • Educating homeowners about altering grade (See the ANHWP “Surface Water Management” Brochure)

  41. Resources • Geotechnical report (for the subdivision) • Site specific borehole and/or lab testing of soil samples • Building on Alberta Soils • On-line course • 1 day lab and field practicum • http://www.albertasoils.com/

  42. Foundation Movement and Heave in Basements Presented by: Charles Kwok, M.Sc., P.Eng. Stantec (Jacques Whitford) Presented in Partnership with: Builder’s Technical Session

  43. SECTION IIICOMPACTION

  44. Compaction Addition of water to dry soil: add water Film of water wraps particles

  45. Compaction Addition of water to moist soil Water takes up more space replaces air

  46. Compaction Addition of water to wet soil No more air voids left, therefore water will begin to displace soil

  47. Settlement - Consolidation Weight (from footing or other) water is pushed out from soil

  48. Settlement - Consolidation Examples of problems encountered poor compaction of granulars organic soil soft clay

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