Environmental Engineering Reference
In-Depth Information
FIGURE 9.104
Cut slopes at the beginning of a 300-m-deep excavation in highly decomposed igneous and metamorphic rocks
for a uranium mine. Bench width is 20 m, height is 16 m, and inclination is 1H:1.5V (57°). Small wedge failure
at right occurred along kaolinite-filled vertical relict joint. Part of similar failure shows in lower left. Slope
monitoring with a convergence meter is shown in
Figure 4.8.
Drains are installed as standard practice along the slopes and the benches to control
runoff as illustrated in
Figure 9.105
to
Figure 9.107.
Failing Slopes
If a slope is failing and undergoing substantial movement, the removal of material from
the head to reduce the driving forces can be the quickest method of arresting movement
of relatively small failures. Placing material at the toe to form a counterberm increases the
resisting forces. Benching may be effective in the early stages, but it did not fully stabilize
the slope illustrated in
Figure 9.29,
even though a large amount of material was removed.
An alternative is to permit movement to occur and remove debris from the toe; eventually
the mass may naturally attain a stable inclination.
Changing slope geometry to achieve stability once failure has begun usually requires
either the removal of very large volumes or the implementation of other methods. Space
is seldom available in critical situations to permit placement of material at the toe, since
very large volumes normally are required.
9.4.3
Surface Water Control
Purpose
Surface water is controlled to eliminate or reduce infiltration and to provide erosion pro-
tection as discussed in detail in
Section 8.2.2.
External measures are generally effective,
however, only if the slope is stable and there is no internal source of water to cause exces-
sive seepage forces.
