Page 363 - Masonry and Concrete

Retaining Walls
362 CHAPTER TEN

of the gravity mass. The reinforcement (either geogrids or geotextiles)
extends through the bed joint between the SRW units and into the soil
to create a composite gravity mass structure. This composite structure
offers increased resistance for taller walls, surcharged structures, or
more difficult soil conditions. With most systems, you can build a 3-
to 4-ft. high wall in good soil without the need for soil reinforcing or
engineering design. As an alternative to a single-high wall in steeply
sloped areas, consider two shorter walls stepped back against the
slope (Figure 10-18).
In soils that drain well, excavate a trench along the length of the wall
6 in. deep and 18–24 in. wide and place a 2-in. sand bed in the trench for
leveling the units. In dense or clayey soils, or in areas that do not drain
well, excavate 4–6 in. deeper and add a gravel or crushed stone drainage
bed. Level the drainage bed with a rake and tamp the gravel to compact
it. Place a layer of landscape filter fabric over the gravel, then add the 2-
in. sand leveling bed. Getting the base course of units level is very impor-
tant to the strength and stability of the wall. Use wooden stakes, a string,
and a line level to maintain the correct elevation.

FIGURE 10-18
Two-level, terraced retaining wall.

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