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.
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- 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
- Helical Pier Shaft:
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