Environmental Engineering Reference
In-Depth Information
Infiltration Protection
Planting the slope with thick, fast-growing native vegetation not only strengthens the
shallow soils with root systems, but discourages desiccation which causes fissuring. Not
all vegetation works equally well, and selection requires experience. In the Los Angeles
area of California, for example, Algerian ivy has been found to be quite effective in stabi-
lizing steep slopes (Sunset, 1978). Newly cut slopes should be immediately planted and
seeded.
Sealing cracks and fissures with asphalt or soil cement will reduce infiltration but will
not stabilize a moving slope since the cracks will continue to open. Grading a moving area
results in filling cracks with soil, which helps to reduce infiltration.
Surface Drainage Systems
Cut slopes
should be protected with interceptor drains installed along the crest of the cut,
along benches, and along the toe (
Figure 9.105).
On long cuts the interceptors are con-
nected to downslope collectors (
Figure 9.106).
All drains should be lined with nonerodable
materials, free of cracks or other openings, and designed to direct all concentrated runoff
to discharge offslope.
With failing slopes
, installation of an interceptor along the crest beyond the head of the slide
area will reduce runoff into the slide. But the interceptor is a temporary expedient, since in
time it may break up and cease to function as the slide disturbance progresses upslope.
Roadway storm water drains
should be located so as to not discharge on steep slopes
immediate adjacent to the roadway. The failure shown in
Figure 9.6
was caused by storm
water discharge through a drain pipe connecting the catch basin on the upslope side of the
roadway with a pipe beneath the roadway which exited on the slope.
9.4.4
Internal Seepage Control
General
Purpose
Internal drainage systems are installed to lower the piezometric level below the potential
or existing sliding surface.
System Selection
Selection of the drainage method is based on consideration of the geologic materials, struc-
ture, and groundwater conditions (static, perched, or artesian), and the location of the
phreatic surface.
Paved ditch
Plant
vegetation
Colluvium
(clayey
silt)
Original
slope
45
°
2 m
34
°
Highly
decomposed
rhyalite tuff
(slightly clayey
silt, highly
erodible)
45
°
10 m
1 m
60
°
FIGURE 9.105
Benching scheme for cut in highly erodable soils in a
tropical climate. Low benches permit maximum inclination
to reduce the effect of runoff erosion. The natural cut before
benching is shown in
Figure 8.5.
Paved ditch for
longitudinal drain
3 m
45
°
60
°
Paved roadway ditch
