Page 361 - Moving the Earth_ The Workbook of Excavation

ROADWAYS

ROADWAYS 8.23

Long slopes may be benched, as in Fig. 8.15(B), to break the flow of surface water. Each bench
has a reverse slope so that it acts as a diversion ditch, with water flowing along the back. A gentle
grade spills the water toward one or both ends of the cut.
Benches may also serve to catch falling rock. Their effectiveness for this is increased by a berm
of dirt along the outer edge. This construction is particularly useful in banks of cemented gravel,
1 on 1 or steeper, from which surface cobbles are released.
Slopes can be stabilized by growth of vegetation. Most types will provide surface protection,
and types with deep or interlocking roots may hold against some internal pressure as well. To help
the revegetation after fire had destroyed grass cover on a steep slope, straw and coconut-fiber
blankets, as seen in Fig. 8.16, were used.
Artificial protections include supporting walls, drainage systems to intercept or remove ground-
water, and fences to catch rolling pieces.
Walls may be of masonry, interlocked concrete, or metal bins. Strength of the last two construc-
tions depends on their being filled with coarse, pervious fill. Any of these must rest on a solid
footing that can resist both weight and thrust.
Logs can be used for temporary retaining walls and to catch boulders rolling during work.

Drainage. Freshly worked embankments should be protected against surface water flowing
from adjoining ground. In cuts, a diversion ditch may be dug a few feet back from the upper edge.
Unless its gradient is gentle, its bottom may need protection to prevent it from developing into a
gully that would damage land below it and eventually break out through the bank.
Such protection may include establishment of a strong sod, construction of a series of check dams,
paving with resistant materials, diversion of some of the natural drainage at higher points, or use
of discharge flumes down the slope.
If the slope is threatened by softening or washing by groundwater, subdrainage may be
required also. Land tile may be laid under the surface channel if its floor is impervious enough not

FIGURE 8.16 Revegetation on a steep slope. (Courtesy of North American Green.)