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APPENDIX 2F
MODEL SPECIFICATIONS
Chapter 2
Helical Foundation Systems
3
DEFINITIONS
3.1 The following terms apply to helical soil nails:
3.1.1 Allowable Stress Design: A structural and geotechnical design methodology that states
that the summation of the actual estimated loads (nominal loads) must be less than or
equal to the allowable design load (required strength). Allowable loads are obtained by
dividing a nominal resistance (strength) by an appropriate factor of safety.
3.1.2 Bearing Stratum: The soil layer (or layers) that provides helical soil nail end bearing
capacity through load transfer from the helical plates.
3.1.3 Crowd: Axial compressive force applied to the helical soil nail shaft as needed during
installation to ensure the soil nail advances at a rate approximately equal to the helix
pitch for each revolution.
3.1.4 Design Loads: A generic and ambiguous term used to describe any load used in design.
It is not specific to factored or unfactored loads or any particular design methodology.
It is a term; therefore, that should be avoided when specifying load requirements. FSI
recommends using the term service load, nominal load or factored load, as described
herein, where applicable.
3.1.5 Design Strength: A term used in structural design which is defined as the product of the
nominal strength and the applicable resistance factor. An equivalent term typically used
in geotechnical design is, also sometimes referred to as factored resistance (Load and
Resistance Factor Design).
3.1.6 Extension Section: Helical soil nail shaft sections connected to the lead section or other
extension sections to advance the helix plates to the required bearing strata and nail
length. Helical soil nail extension have helix plates.
3.1.7 Factor of Safety: The ratio of the ultimate soil nail capacity or nominal resistance (strength)
to the nominal or service load used in the design of any helical soil nail component or
interface (Allowable Stress Design).
3.1.8 Factored Load: The product of a nominal load and an applicable load factor (Load and
Resistance Factor Design).
3.1.9 Factored Resistance: The product of a nominal resistance and an applicable resistance
factor (Load and Resistance and Factor Design).
3.1.10 Geotechnical Capacity: The maximum load or the load at a specified limit state, that can
be resisted through the soil nails interaction with the bearing soils (see also Ultimate Soil
Nail Capacity).
3.1.11 Helical Soil Nail: Consists of a central steel shaft with multiple helix-shaped bearing
plates and a load transfer device that allows attachment to wall or slope facing
components. Helical soil nails are installed into the ground by application of torque and
axial compressive force (“crowd”).
