Page 357 - Masonry and Concrete

Retaining Walls
356 CHAPTER TEN

10-11). Space the weeps 32 in. to 48 in. on center. In areas where pre-
cipitation is heavy or where poor drainage conditions exist, prolonged
seepage through weep holes can cause the soil in front of a retaining
wall and under the toe of the footing to become saturated and lose some
of its bearing capacity. In these instances, a continuous drain of perfo-
rated pipe should be placed behind the wall near the base but above the
bottom of the footing, with discharge areas located beyond the ends of
the wall (Figure 10-12).
Coarse gravel backfill behind concrete or masonry retaining walls
should extend from the top of the footing to within 12 in. of finished
grade, be 2 ft. wide, and run the entire length of the wall. To prevent the
infiltration of fine soil, a layer of roofing felt or landscape fabric should
cover the gravel. Waterproofing requirements for the back face of a
retaining wall will depend on the climate, soil conditions, and type of
masonry units used. Seepage through a masonry wall can cause efflo-
rescence or calcium carbonate stains, but a waterproof membrane will
keep the wall from being saturated. Walls of porous concrete block
should always be waterproofed because of the excessive expansion and

1" PVC PIPE

FIGURE 10-11
Weep hole in masonry retaining wall.

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