Page 360 - Masonry and Concrete

Retaining Walls
359
RETAINING WALLS

be either single or multiple unit depths. Soil-
reinforced SRWs are composite systems con-
sisting of SRW units in combination with a
mass of retained soil stabilized by horizontal
layers of geosynthetic reinforcement materi-
als (Figure 10-15). Some systems can be laid
in either straight or curved lines, but others GRAVEL
are limited to straight walls and 90-degree SINGLE DEPTH BACKFILL
FOR
corners. No mortar is required for SRW sys- DRAINAGE
tems, but the units must be restrained
against sliding by either a physical inter-
locking shape or a shear connector such as
rods, pins or clips (Figure 10-16).
Because they are dry-stacked, segmen-
tal retaining walls are flexible and can
tolerate minor movement and settlement
without distress. The units are not
mortared together, so they expand and
contract freely and do not require expan-
sion or control joints. SRWs also permit MULTIPLE DEPTH
water to drain directly through the face of FIGURE 10-14
the wall so hydrostatic pressure is elimi- Single- and multiple-depth segmental retaining
nated and weep holes are not necessary. walls. (from National Concrete Masonry Association,
Water drainage through the face of the Design Manual for Segmental Retaining Walls, NCMA,
Herndon, VA).
wall, however, would result in staining,
efflorescence, and possible freeze-thaw damage if the units remained
saturated from wet soil. Primary drainage is provided by gravel back-
fill, and in very wet areas includes drain lines at the base of the wall.
This moves moisture quickly to the bottom of the wall and limits to
the base course any staining which might occur. SRWs are typically
supported on gravel bed foundations instead of concrete footings.
The maximum height that can be constructed using a single-unit-
depth conventional SRW is directly proportional to its weight,
depth, and vertical batter for any given soil type and slope condi-
tions (Figure 10-17).
The allowable height of a wall can be increased by using multiple
unit depths or soil-reinforced systems. Soil-reinforced SRWs use
geosynthetic reinforcement to enlarge the effective width and weight

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