Design Examples

  • Given:Foundation Repair of wall due to settlement.
    • Design loan per pier = 18,000 lbs.
    • Underlying Soil Strata:
      • 0 to 5 feet uncontrolled fill
      • Overlying stiff clay with N values of 20 at
      • 10 feet, 40 feet at 20 feet and 50 at 30 feet.
    • Factor of safety = 2
  • Find:Sizes of helix pier shaft and helix (helices) required to support the design load.
    • Required installation torque.
    • Required depth of pier below foundation grade.
    • Required pier attachment to foundation.
      • Helical Pier Shaft:
        • 1 ½ inch square shaft
        • (ASTM A576, Grade C-1045)
        • Working Capacity = 35 kips (F.S. = 2)
        • Design Pier Load = 18 kips
      • Helix (Helices):
        • Single ½ inch thick, 8 inch diameter helix
        • (ASTM A36)
        • Working Capacity = 27.5 kips (F.S. = 2)*
        • Design Pier Load = 18 kips
      • Installation Torque:
        • Torque required = 18,000 lbs / 10 ft-1
        • 1,800 ft lbs of torque
        • Ultimate torque capacity = 6,000 ft lbs *
        • Design Pier Load = 18 kips
        • Required torque capacity = 1,800 ft lbs of torque
      • Required depth of Pier:
        • Pier to extend through fill material, into stiff clay below.
        • Pier depth to be determined when installation torque is attained.
        • Minimum pier length is recommended to be 20-feet below foundation grade.
      • Required Pier Attachment:
        • Standard Bracket
        • (ASTM A36)
        • Working Capacity = 27.5 kips (F.S. = 2)*
        • Design Pier Load = 18 kips