Technical Manual

Inc.

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Chapter 2

Helical Foundation Systems

CHAPTER 2

HELICAL FOUNDATION SYSTEMS

2.2 – Summary Description

Helical piles are a factory-manufactured

steel foundation designed to resist axial

compression, axial tension, and/or lateral loads

from residential and commercial structures. The

system consists of a central shaft, one or more

helix-shaped bearing plates, and a bracket that

allows attachment to structures. The helix plates

are commonly referred to as blades or flights

and are welded to the lead section. Extension

shafts, with or without additional helix plates,

are used to extend the pile to competent load

bearing soil and to achieve design depth and

capacity. Brackets are used at the tops of the

piles for attachment to structures, either for new

construction or retrofit applications. Helical piles

are advanced (screwed) into the ground with the

application of torque.

The terms helical piles, screw piles, helical piers,

helical anchors, helix piers, and helix anchors

are often used interchangeably by specifiers.

However, the term “pier” more often refers to a

helical pile loaded in axial compression, while

the term “anchor” more often refers to a helical

pile loaded in axial tension. The term “pile”

traditionally describes a deep foundation that

can resist both tension and compression loads.

Helical tiebacks and helical soil nails are

types of helical anchors differentiated by their

specific design methodology and/or installation

orientation. Helical tiebacks are designed similarly

but differ from vertically-installed helical piles in

that they are typically installed in a horizontal to

45-degree downward from horizontal orientation

to laterally support the tops of earth retaining

structures; e.g., retaining walls, foundation walls,

sheet pile walls, soldier pile walls with wood

lagging, etc. Helix plates are typically limited to

the lead section or the lead and first extension

of the tieback. Multi-helix leads for piles and

tiebacks generally consist of increasing plate

sizes from the tip. Helical soil nails are designed

with same-sized helix plates, typically 6 or 8

inches in diameter, spaced evenly along the

entire length of the nail, including the lead and

extensions. Soil nails are typically installed in a

closely-spaced grid pattern to reinforce the soil

and provide a stable earth mass. Helical tiebacks

and helical soil nails are presented in their own

sections later in this chapter.

New construction helical pile installation

Sheet pile wall stabilization

with helical tiebacks

Helical tieback installation

with hand-held equipment