Page 354 - Masonry and Concrete

Retaining Walls
353
RETAINING WALLS

concrete masonry cantilever walls will depend on the amount of pre-
fabricated joint reinforcement used. Figure 10-8 shows maximum joint
spacing. Joints can also be located so that they form wall panels of
approximate square shape, so for a 4-ft.-high wall, control joints would
be located at 4 ft. on center, and so on. This type of spacing will provide
the greatest protection against random shrinkage cracks forming in the
wall.
The table in Figure 10-9 gives recommended design requirements
for double-wythe, grouted brick retaining walls up to 4 ft. high. The
brick should be Grade SW with a compressive strength of at least 5,000
psi, and the mortar should be Type M. The reinforcing dowels in the
footing must be located along the center line of the wall so that they
will fit properly between the two brick wythes. In addition to the steel
bars required by the tables, prefabricated wire joint reinforcement
should be installed in the mortar bed joints every 16 in. or 6 courses.
This will tie the two wythes of brick together, and it will increase the
strength of the wall. Expansion joints should be located in brick retain-
ing walls every 16–20 ft. on center. The joint should actually be a com-
plete separation between two adjacent wall sections, and the joint
should be caulked with a high-performance exterior sealant. This will
allow the two sections to expand freely with changes in moisture con-
tent.

10.2.3 Drainage and Waterproofing
Drainage and waterproofing for cantilever retaining walls is similar to
that required for basements. In this case, the protection is required for
the wall itself rather than for an occupied space. A buildup of moisture

Recommended Spacing Vertical Spacing of Joint Reinforcing
of Control Joints None 24 inch 16 inch 8 inch
1
Expressed as ratio of 2 2 ⁄2 3 4
panel length to panel
height, L/H

FIGURE 10-8
Recommended control joint spacing for concrete masonry. (adapted from NCMA, TEK 10-
1, National Concrete Masonry Association, Herndon, VA).

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