Civil Engineering Reference
In-Depth Information
Stabilization of rock slopes
12.1 Introduction
In mountainous terrain, the operation of
highways and railways, power generation and
transmission facilities, and the safety of residen-
tial and commercial developments often require
stable slopes and control of rock falls. This applies
to both excavated and natural slopes. In con-
trast, open pit mines tolerate a certain degree of
slope instability unless there is a hazard to the
miners or a significant loss of production. For
example, minor failures of benches usually have
little effect on operations unless the fall lands on
a haul road and results in tire or equipment dam-
age. In the event of a large-scale slope failure in
an open pit mine, often the only economic and
feasible stabilization measure is drainage, which
may involve long horizontal drains, pumped
wells or drainage adits (see Section 12.4.6). A
more common means of managing large-scale
slope instability is to monitor the movement
so that mining can continue beneath the mov-
ing slope. Procedures for monitoring movement
and
indirect economic losses. For railroads and toll
highways, closures result in a direct loss of rev-
enue. Figure 12.1 shows a rock slide that occurred
from a height of about 300 m above the road and
closed both the road and an adjacent railway.
While the cost of a slide, such as that shown in
Figure 12.1 is substantial, the cost of even a single
vehicle accident can be significant. For example,
costs may be incurred for hospitalization of the
driver and passengers, for repair to the vehicle,
and in some cases for legal charges and com-
pensation payments. Often there are additional
costs for stabilization of the slope that will involve
both engineering and contracting charges, usu-
ally carried out at premium rates because of the
emergency nature of the work.
Many transportation systems were constructed
over a century ago in the case of railroads, and
decades ago in the case of many highways. At
that time, the blasting techniques that were often
used in construction caused significant damage to
the rock. Furthermore, since the time of construc-
tion deterioration of stability conditions is likely
due to weathering of the rock, and loosening of
the surficial blocks by ice and water, and by the
growth of tree roots. All these effects can result in
on-going instability that may justify remediation
programs.
For urban developments in mountainous ter-
rain, hazards that can threaten or even destroy
structures include rolling boulders and landslides.
The most effective protection against these condi-
tions is initial hazard mapping, and then zoning
interpreting
the
results
are
discussed
in
Chapter 13.
This chapter is concerned mainly with civil
slopes because the high cost of failures means
that stabilization programs are often economic-
ally justified. For example, on highways, even
minor falls can cause damage to vehicles, injury
or death to drivers and passengers, and possibly
discharge of toxic substances where transport
vehicles are damaged. Also, substantial slope
failures on transportation systems can severely
disrupt traffic, usually resulting in both direct and
