Transmission And Substation Foundations - Technical Design Manual (TD06088E)

For example, a Type SS175 helical pile in firm soil & fixed end condition with multi-helix plates (3 or more plates) has ASD allowable compression strength of 98.3 kip. However, that exceeds the P4 geotechnical allowable capacity of 52.5 kip. But if the soil is soft with the same fixed end condition, the ASD allowable compression strength is 30.2 kip; which is less than the P4 geotechnical allowable capacity of 52.5 kip. The difference is the depth to fixity, which is 5’-0 in firm soils and 10’-0 in soft soils. The table below from Section 7 of the TDM lists the P1 (new construction bracket) and P2 (shaft) ASD allowable strengths for Type SS175 helical piles. It is used to easily determine P1 and P2, which can then be compared to P4 to see which will control the design. The table is broken down by concrete strength, soil type and end condition.

Table C-5 - SS175 – P1 Pile Cap Compression Strength and P2 Shaft Compression Strength in Firm and Soft Soils

HELICAL PILES AND ANCHORS

For example, a Type SS175 helical pile in firm soil & fixed end condition with a new construction cap em- bedded in 2500 psi concrete has an ASD allowable compression strength of 52.7 kip based on the strength of the cap (P1). The P4 geotechnical allowable capacity of 52.5 kip is basically the same. But if the soil is soft with the same fixed end condition, the ASD allowable compression strength is 30.2 kip based on the shaft strength; which is less than the P4 geotechnical allowable capacity of 52.5 kip. Again, the difference is the depth to fixity, which is 5’-0 in firm soils and 10’-0 in soft soils. The table below from Section 7 of the TDM lists the P1 (remedial repair bracket) and P2 (shaft) ASD al- lowable strengths for Type SS175 helical piles. It is used to easily determine P1 and P2, which can then be compared to P4 to see which will control the design. The table is broken down by concrete strength and soil type. CHANCE Remedial Repair Brackets provide fixed end condition at the bracket-shaft connection.

Table C-6 - SS175 – P1 Repair Bracket Compression Strength and P2 Shaft Compression Strength in Firm and Soft Soils

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