Page 356 - Masonry and Concrete

Retaining Walls
355
RETAINING WALLS

behind retaining walls causes hydrostatic pressure which can signifi-
cantly increase the loads on the wall. Concrete retaining walls can be
drained to avoid hydrostatic pressure buildup using a length of PVC
pipe placed in the bottom of the forms at a point just above finish grade.
This will form an open drain tube through the concrete. To hold the
tube in place during the concrete pour, drive a screw through the form-
work at each side (Figure 10-10). Space the weep tubes 3 to 4 ft. on cen-
ter. For well-drained soils, a 1-in. pipe diameter should be adequate.
For wetter soils, a little larger-size PVC may be necessary. Use a piece
of screen wire to keep the gravel backfill out of the weep tube. Weeps
in brick and concrete masonry building walls are formed by omitting
the mortar from head joints at the base of the wall. In a grouted retain-
ing wall, however, a PVC tube works better. Lay the pipe across the
masonry, setting the front end flush with the face of the wall, cut the
brick or block to fit around it, and mortar the space in between (Figure

GRAVEL DRAINAGE LAYER

ROOFING FELT OR
LANDSCAPE FABRIC
TO PREVENT
CLOGGING
GRAVEL
WEEP TUBE

SCREEN WIRE
TO PREVENT
CLOGGING
DRAIN TUBE

FIGURE 10-10
Weep hole in concrete retaining wall.

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