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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