Environmental Engineering Reference
In-Depth Information
Unstable cut slopes in the process of failure need treatment, but stabilization may not be
economically practical.
New slopes formed by cutting or filling may require treatment by some form of stabi-
lization.
Initial Assessment
An initial assessment is made of the slope conditions, the degree of the hazard, and the
risk. There are then three possible options to consider for slope treatment:
avoid the high-risk hazard, or
accept the failure hazard, or
stabilize the slope to eliminate or reduce the hazard.
Treatment Options
Avoid the High-Risk Hazard
Conditions: Where failure is essentially not predictable or preventable by reasonable means
and the consequences are potentially disastrous, as in mountainous terrain subject to mas-
sive planar slides or avalanches, or slopes in tropical climates subject to debris avalanches,
or slopes subject to liquefaction and flows, the hazard should be avoided.
Solutions : Avoid development along the slope or near its base and relocate roadways or
railroads to areas of lower hazard where stabilization is feasible, or avoid the hazard by
tunneling.
Accept the Failure Hazard
Conditions: Low to moderate hazards, such as partial temporary closure of a roadway, or a
failure in an open-pit mine where failure is predictable but prevention is considered
uneconomical, may be accepted.
Open-pit mines: Economics dictates excavating the steepest slope possible to minimize
quantities to be removed, and most forms of treatment are not feasible; therefore, the haz-
ard is accepted. Slope movements are monitored to provide for early warning and evacu-
ation of personnel and equipment. In some instances, measures may be used to reduce the
hazard where large masses are involved, but normally failures are simply removed with
the equipment available.
Roadways: Three options exist besides avoiding the hazard, i.e., accept the hazard,
reduce the hazard, or eliminate it. Acceptance is based on an evaluation of the degree of
hazard and the economics of prevention. In many cases involving relatively small volumes
failure is self-correcting and most, if not all, of the unstable material is removed from the
slope by the failure; it only remains to clean up the roadway. These nuisance failures com-
monly occur during or shortly after construction when the first adverse weather arrives.
The true economics of this approach, however, depends on a knowledgeable assessment
of the form and magnitude of the potential failure, and assurance that the risk is low to
moderate. Conditions may be such that small failures will evolve into very large ones, or
that a continuous and costly maintenance program may be required. Public opinion
regarding small but frequent failures of the nuisance type also must be considered.
Eliminate or Reduce the Hazard
Where failure is essentially predictable and preventable, or is occurring or has occurred
and is suitable for treatment, slope stabilization methods are applied. For low- to moder-
ate-risk conditions, the approach can be either to eliminate or to reduce the hazard,
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