Transmission And Substation Foundations - Technical Design Manual (TD06088E)

Section 7 is broken down by specific helical pile product families. Each family sub-section lists the tension and compression strengths in various tables, in addition to specifications and available configurations. For example, the P2 (shaft) strength and P4 (geotechnical) tension capacity for Type SS175 helical piles are shown below.

Table C-3 - SS175 - P2 Tension Strength and P4 Torque Correlated Capacity

The pre-qualified and verified torque correlation factor (Kt) is 10 for Type SS175. The torque rating for SS175 is 10,500 ft-lb. Therefore, per P4 [Method 2] , the torque correlated capacity limit for SS175 is 105 kip (see Section 6 TDM). The nominal strength of Type SS175 shaft (P2) is limited to 100 kip by the shear strength of the coupling bolt. Comparing the two, 105 kip > 100 kip, therefore P2 tension strength controls at max torque. If the installation torque is less than 10,000 ft-lb, then P4 [Method 2] will control. The al- lowable geotechnical capacity of 52.5 kip is based on a deterministic factor of safety of 2. It is convenient to tabulate axial compression strength in terms of either P2 (shaft) & P3 (helix), or P1 (bracket) & P2 (shaft). The table below from Section 7 of the TDM lists the P2 (shaft) and P3 (helix) ASD allowable strengths for Type SS175 square shaft helical piles. It is used to easily determine P2 and P3, which can then be compared to P4 to see which will control the design. The table is broken down by soil type, end condition, and number/diameter of the helix plates.

HELICAL PILES AND ANCHORS

Table C-4 - SS175 - P2 Shaft Compression Strength and P3 Helix Strength in Firm or Soft Soil

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