Foundations and Site Preparation

Read Ching, Chapters 1, 2 & 3

  1. Purpose of the building foundation: carry building loads to the ground

    2.  
  2. Types of foundations
    1. Continuous spread footings
    2. Piers and grade beams
    3. Piles and grade beams
    4. Caissons and grade beams
    5. Raft (4' to 8' thick reinforced concrete slab)
    6. Floating (weight of earth excavated = total building load)
      1. Basement is designed like a truss
      2. Foundation must be rigid

  3. Soils
    1. Surface of earth is overlaid with:
      1. Bedrock (The Teton Mountains are exposed bedrock, for example)
      2. Water
      3. Unconsolidated material (soil) formed by disintegration of bedrock
        1. "Undisturbed" soil
        2. "Organic" materials (dead animals or plants)
        3. Fill
        4. Engineered fill
    2. Soil classification
      1. Granular (grain size classification by USDA)
        1. Sand: 1/5000" to 1/500" in diameter
        2. Gravel: greater than 1/12" in diameter
      2. Cohesive
        1. Silt: 1/12500" to 1/5000" in diameter
        2. Clays: less than 1/12500" in diameter
      3. Organic (not suitable for foundations)
        1. "Black dirt" (it is great for growing crops in, though)
        2. "top soil"
        3. peat
        4. loam

  4. Design of footings based on allowable soil pressures
    1. Allowable soil pressures
      1. Determined by testing - taking "borings" on the site
      2. Typical range from 2000 to 6000 pounds per square foot (psf)
    2. Settlement
      1. Settlement is normally expected
        1. Maximum of 1" settlement is typical
        2. Consistency of settlement is desirable
          3.
      2. Causes of settlement
        1. Reduction of volume of voids in the soil
        2. Lowering of the water table
        3. Rupture of the soil
        4. Lateral displacement (sliding)
        5. Compression of the grains

  5. Frost heave
    1. "Frost line" - 3'-6" below grade in most areas around Chicago (Note: some suburbs of Chicago require minimum depth of foundations to be 4'-0" below grade)
    2. "Frost walls" for light loads such as porches, stoops, or fence walls.
    3. Stoop arms

  6. Water table
    1. Moisture in soil between grains
    2. Ground water level
    3. Trapped water (perched water tables)
    4. Dewatering during construction
    5. Dangers of lowering water table
    6. Dampproofing of foundations
    7. Sub-soil drains
    8. Waterproofing of foundations

  7. Ventilation of basements and crawl spaces
    1. Purposes of ventilation
    2. Basements: 2% of floor area
    3. Crawl spaces
      1. Without vapor retarder: 1/150 of crawl space area
      2. With 6 mil polyethelene vapor retarder: 1/1500 of crawl space area

  8. Site Preparation

    Equipment used

  9. Bulldozers

  10. Grader

  11. Front end loaders

  12. Hydraulic excavator

  13. Back Hoe




    14. 14. Skid Steer Loader

    15. Wheel Loader