Transmission And Substation Foundations - Technical Design Manual (TD06088E)

Soil Profile:

Figure 7-26

CHANCE® Helical Pile Selection RS2875.203 with 8-10-12 helix configuration

Ultimate Pile Capacity

Equation 7-7

• Q t = (A 8 + A 10 + A 12 ) c N c A 8 , A 10 , A 12 = Projected area of helical plates. A 8 = 0.34ft 2 A 10 = 0.53 ft 2 A 12 = 0.77 ft 2 N c = Bearing Capacity Factor = 9.0 C = N/8 = 16/8 = 2 ksf • Q t = (1.64ft 2 )(2,000 psf) ( 9.0) • Q t = 29,520 lb (installed depth is over 20 ft) Check Qt • Conduct Field Load Test (if required per specifications) Estimate installation Torque

DESIGN EXAMPLES

Equation 7-8

P = 56,000lb/4 Piles = 14,000 lb T = (P X FS)/K t = (14,000 lb x 2)/9 = 3,150 ft-lb K t = empirical torque factor (default value =9 for the RS2875 series) The rated installation torque of the RS2875.203 series is 5500 ft-lb, which greater than the required estimated installation torque of 3,150 ft-lb. (OK) NOTE: If during installation T = 3,150 ft-lb is not achieved then two options are available: (1) add piles if spacing allows, or (2) change helix configuration to a larger combination, i.e, (10-12-14) (3) Install Deeper Factor of Safety Equation 7-9 • Theoretical Ultimate Capacity FS = (Q t /P) = 29,520/14,000 = 2.1 (OK) • Torque Correlation: FS = (T x K t )/P FS = (3,150 x 9)/14,000 = 2.03 (OK)

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