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p 33
Chapter 2
Helical Foundation Systems
CHAPTER 2
HELICAL FOUNDATION SYSTEMS
2.9 Helical Soil Nails
Soil nailing is a method of earth retention that
relies on a grid of individual reinforcing strands
or members installed within a soil mass to
create an internally stable gravity wall/retaining
system. Soil nail wall technology began in
Europe with use of the New Austrian Tunneling
Method in rock formations in 1961. The
technology then carried over to applications
involving unconsolidated soil retention,
primarily in France and Germany. Soil nail walls
were first used in North America for temporary
excavation support in the late 1960s and
continued to gain recognition and acceptance
during the 1970s and 1980s for higher profile
projects including highway applications. Much
of the soil nail wall research performed in North
America was funded by the Federal Highway
Administration (FHWA) and other state highway
agencies during the 1990s. Although helical
piles have been used as tiebacks since the
early 1950s, helical soil nails are a relatively
new alternative to their grouted counterparts.
Soil nail walls offer the following advantages
over tieback walls as well as other top down
construction techniques:
• Soil nail walls are more economical than
conventional concrete gravity walls and are
often more economical than tieback walls due
to reduced wall facing requirements. There
would likely be more soil nails than tiebacks for
a given project, but this additional cost for the
nails is outweighed by the difference in cost of a
shotcrete facing versus a more substantial soldier
pile, sheet pile, or reinforced concrete wall detail.
• Soil nails are typically shorter than tiebacks for
similar wall heights so there will be reduced
right-of-way (ROW) requirements.
• There is less impact to adjacent structures since
soil nail walls are not installed with vibratory
energy like soldier piles or sheet piles.
• Overhead clearance requirements are less than
driven soldier pile or sheet-pile wall construction.
Soil nail walls can therefore be installed easily
below bridges and even within existing buildings.
Figure 2.9.a2
Figure 2.9.a1
Helical soil nail wall installation
