Design Example

Given: Foundation repair of wall due to settlement.
Design load 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 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.

• Helix Pier Shaft: 11/2 inch square shaft
  (ASTM A576, Grade C-1045)
  Working Capacity = 35 kips (F.S. = 2)*
  Design Pier Load = 18 kips
• Helix (Helices): Single 3/8 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 = 30 kips (F.S. = 2)
  Design Pier Load = 18 kips