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Chapter 2
Helical Foundation Systems
CHAPTER 2
HELICAL FOUNDATION SYSTEMS
Plate brackets can be cast into the concrete of
a poured concrete wall or mounted to the face
of an existing concrete wall, sheet pile wall, or
soldier beam and lagging wall. Waler beams
may also be considered to more uniformly
spread the tieback or soil nail load to the wall
(Figure 2.3.3.d)
.
Foundation Supportworks recommends that
all helical anchors and tiebacks (excluding
soil nails) be pre-tensioned or proof-tested
following installation. Pre-tensioning to 1.0 to
1.33 times the design working load minimizes
deflection of the tiebacks and structure as
the tiebacks are put into service and the soil
strength around the helix plates is mobilized.
Tiebacks installed to support existing walls
are typically locked off at 0.75 to 1.1 times
the design working load after proof-testing.
Helical anchors and tiebacks to be cast
into new concrete retaining walls may be
completely unloaded, or locked off with a
modest seating load, after proof-testing.
Tiebacks can be “pull tested” or load tested
to typically two (2) times the design working
load or more to identify the ultimate system
capacity, better assess soil conditions and
soil/anchor interaction, and validate design
assumptions and parameters. Tiebacks that
undergo load testing to greater than 1.5
times the design working load, or failure, are
generally considered sacrificial and should
not be used as production tiebacks.
Specialty brackets may be required for certain
projects. Some of the more common specialty
brackets are often modified in their dimensions,
material properties, material thicknesses,
and/or connection details from project to
project due to variations in the design loading
and/or construction. Specialty brackets are
available for deck supports, boardwalk projects
(Figures 2.3.3.e1 and 2.3.3.e2)
, elevated
structures in high tide or hurricane-prone areas,
pipe buoyancy control, guy wires, tie downs,
etc. Contact FSI with any questions regarding
bracket details or availability.
Figure 2.3.3.d
Schematic of helical
tieback and pre-tension assembly
Figure 2.3.3.e1
Boardwalk supported on
2.375” O.D. vertical and battered helical piles
Figure 2.3.3.e2
Custom saddle bracket
connected with clevis to battered helical pile