Transmission And Substation Foundations - Technical Design Manual (TD06088E)

DESIGN EXAMPLES

Figure 7-10: Resultant Deflection, Moment, and Shear

When looking at the GROUP® results, the important things to look for in Figure 7-10 are: Is the resultant deflection greater than acceptable and is the moment greater than allowable. For a pulldown pile, the acceptable moment is either 0.6 Mp of the casing or the cracking moment. In this case, the cracking moment is 10.6 kip-in. The minimum depth of grout for the piles is where the resultant shear becomes very close to 0 (less than 50 lbs). This is the location where the square shaft no longer requires the grout column (assuming the soil is greater than 4 blow materials). The minimum depth of the grout column in this example is 16 ft. The minimum depth of casing is the deepest depth at which the resultant moment is equal to the cracking moment of the uncased shaft. In this case the minimum cased depth is 14 ft.

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