Transmission And Substation Foundations - Technical Design Manual (TD06088E)

Lead Section and Extensions

The starter section or “lead” section contains the helix plates. This lead section can consist of a single helix or up to four helices. Additional helix plates can be added, if required, with the use of helical extensions. Standard helix sizes and areas are shown in Table 6-2 and 6-3 below. Tables 6-2 and 6-3 provide the projected areas of the most common helix plate diameters. Table 6-2 provides helix areas for Type Square Shaft Helical Piles, and Table 6-3 provides helix areas for Type Round Shaft Helical Piles. The full plate projected area includes the area occupied by the central steel shaft. The “area less shaft” is the projected area of the helix plates less the area occupied by the center shaft. Most all CHANCE® helix plates are provided with a sharp leading edge, which is the front edge of the helix that penetrates the soils as the helical anchor/pile is advanced clockwise though soil. The sharp leading edge enables the helix to better slice through tough soils, roots, and seasonally frozen ground. Hubbell Power Systems, Inc. offers several helix plates with “sea shell” leading edges as special options to the product series. Our standard “sea shell” configuration that works best in most tough soils conditions is the 90° design as shown below. The sea shell cut is a leading edge with a “spiral” cut that is very effective when installing helical piles/anchors in debris laden soils, cobbles, and weathered rock. However, it is important to remember that the bearing capacity of the helical pile/anchor is reduced because the bearing surface area is reduced. Therefore, larger helix diameters or additional helix plates may be required when using “sea shell” cut plates. Tables 6-2 and 6-3 include the projected areas of helix plates offered STANDARD SEASHELL SHAFT SIZE SHAFT SIZE

with the sea shell cut. The helix plates are arranged on the shaft such that their diameters increase as they get farther from the pilot point. The practical limits on the number of helices per pile/anchor is four to five if placed in a cohesive soil and six if placed in a cohesionless or granular soil. Plain extensions are then added in standard lengths of 3, 5, 7 and 10 feet until the lead section penetrates into the bearing strata. Standard helix

LEADING EDGE

PLATE DIA.

STANDARD

SEASHELL

Pipe Shaft

DRAWINGS AND RATINGS

PLATE DIA

PLATE DIA

SHAFT SIZE

configurations are provided in the product series tables in this section. Note that lead time will be significantly reduced if a standard helix configuration is selected.

SHAFT SIZE

LEADING EDGE

Figure 6-2 Square Shaft

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