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Chapter 4
Miscellaneous Structural Support Products
CHAPTER 4
MISCELLANEOUS STRUCTURAL SUPPORT PRODUCTS
4.2.3 Why It Works
With all these caveats in the analysis it might
appear that providing a plausible explanation
for why these systems are so effective would be
impossible. Actually, it’s quite the opposite. Without
the discussion above, one may find it difficult to
understand why these systems work so well. After
all, the wall often straightens over time when the
anchors are tightened to the recommended torque
and at the recommended schedule. This is a
measurable effect. The wall is contacting a great
deal more soil than the earth anchors, so how is it
possible to straighten the wall without pulling the
earth anchors through the soil?
The answer is actually quite simple. Structures
with below ground basements are typically
constructed in areas where clay soils are present
near the surface. Clay soils have cohesive
properties as well as the potential for volume
changes with variations in moisture levels. This
means that during dry periods, the soils can shrink
away from the foundation wall. The cohesive
properties in the soil allow it to stand on its own
and create thin spaces between the soil and the
foundation wall. The tension on installed anchor
rods then decreases. This creates an opportunity
to tighten the anchors and take advantage of the
gaps that have formed between the foundation
wall and soil. This moves the wall slightly closer
to a straight position. This cycle can be repeated
until the desired result is achieved. This also
explains why some walls will see better results
than others. If the soil is particularly sandy, it will
not generally be as cohesive meaning that even
during dry periods, the soil will not relieve the
pressure on the anchors. Although wall anchor
systems are still effective in arresting further
appreciable movement in these types of soils,
the likelihood that the position of the wall will
improve is reduced.
The most important functional consideration
for an “active” resistance system such as earth
anchors is to provide steady, constant pressure
to the wall during the wall straightening process.
4.2.4 Installation Guidelines
Although many of the forces involved are difficult
to quantify, the successful performance of the
product is undeniable. This therefore leaves us
with experience. In the following subsections, we
offer general installation guidelines for spacing,
tightening, and depth and location of the earth
anchor. Deviations to these guidelines may be
considered by a qualified design professional
based on project-specific variables.
Literally thousands of basement walls have been
stabilized with these guidelines and with great
results. Non-typical applications, walls that
are significantly compromised, walls that have
evidence of shear displacement at the bottom,
or walls that are more than 2 to 3 inches out of
plumb should be given special consideration.
4.2.4.1 Spacing
The designer will consider several factors when
providing recommendations for anchor spacing.
These factors include thewall height and thickness,
the retained height of the backfill, and the general
condition and position of the wall. One of the most
common situations is for an 8-inch-thick concrete
block residential basement wall that is 9 feet tall
with 8 feet of unbalanced fill. This scenario most
commonly results in a spacing recommendation of
5 feet between anchors and 3 feet from corners.
Another common situation would be for an 8-inch-
thick poured concrete residential basement wall
that is also 9 feet tall with 8 feet of unbalanced fill.
This scenario most commonly results in a spacing
recommendation of 6 feet between anchors and
3.5 feet from corners.
4.2.4.2 Torque Recommendations
Torque applied to the nuts during the tightening
process of the wall anchor system correlates
directly to tension in the rod and force applied to
the wall. FSI recommends that applied torque not
exceed 80 foot-pounds (ft-lb) for block walls and
90 ft-lb for poured concrete walls. These torque
values assume that FSI Anchor Wax is applied