Chance Technical Design Manual

DESIGN EXAMPLE 3: HELICAL PILE FOUNDATION FOR NEW CONSTRUCTION

BUILDING TYPE • Two story residence • Slab on grade

• Masonry wall, wood frame • Width = 30 ft, L/W = 1-1/2

DESIGN EXAMPLES

STRUCTURAL LOADS

EQUATION 8-9

P = DL + LL + SL P = 1540 + 346 + 162 = 2,048 lb/ft

where

P = Total Load on perimeter footing DL = Dead Load (1,540 lb/ft) LL = Live Load (346 lb/ft) SL = Snow Load (162 lb/ft)

(See Tables 4-1 and 4-4 in Section 4 for DL and LL)

Factor of Safety (FS) = 2.0 (minimum)

PILE SPACING

EQUATION 8-10

Estimated working load = P w = xP Estimated pile spacing (x) = 6.0 ft P w = 6.0 x 2,048 = 12,288 lb

CHANCE® HELICAL PILE SELECTION RS2875.203 with 8-10-12 helix configuration

ULTIMATE PILE CAPACITY

EQUATION 8-11

Q t = ( A 8 + A 10 + A 12 ) c N c

where A 8 , A 10 , A 12 = Projected area of helical plates A 8 = 0.34 ft 2 A 10 = 0.53 ft 2 A 12 = 0.77 ft 2

c = 2,000 psf (based on N = 16 – Equation 5-41) N c = Bearing capacity = 9.0 Q t = (1.64) (2,000) (9.0) Q t = 29,520 lb (installation depth is over 20 ft) CHECK Q t • Conduct Field Load Test (if required per specifications)

HELICAL PILE FOUNDATION, FIGURE 8-1

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