Transmission And Substation Foundations - Technical Design Manual (TD06088E)

DESIGN EXAMPLE 6 HELICAL PILE FOUNDATION FOR NEW SUBSTATION CONSTRUCTION SYMBOLS USED IN THIS DESIGN EXAMPLE

P.................................................................ALLOWABLE DESIGN LOAD 7-38 FS..............................................................................FACTOR OF SAFETY 7-38 Q t ...................................................................ULTIMATE PILE CAPACITY 7-38 K t ........................................................... TORQUE TO CAPACITY RATIO 7-38 A...........................................................................AREA OF HELIX PLATE 7-38 C..................................................................................COHESION OF SOIL 7-38 N c ............................................................BEARING CAPACITY FACTOR 7-38 T....................................................................................................... TORQUE 7-38 N................................................................................. SPT BLOW COUNTS 7-38

DESIGN EXAMPLES

Purpose This design example is intended to assist with the design of new construction substation structures that require deep piles beneath a concrete cap for compression capacity. This example will show how to calculate the bearing capacity of four piles beneath a 10 feet square concrete cap holding an oil filled transformer. After the loads for the structure have been determined, it is possible to design the piles. For this example the working load is as follows: • Compression: 56 kip (Load includes weight of concrete cap) • Shear loads are assumed to be taken by up by passive pressure and fiction along the bottom of the concrete cap.

Figure 7-24

Figure 7-25

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