Civil Engineering Reference
In-Depth Information
Movement monitoring
13.1 Introduction
Many rock slopes move to varying degrees during
the course of their operational lives. Such move-
ment indicates that the slope is in a quasi-stable
state, but this condition may continue for many
years, or even centuries, without failure occur-
ring. However, in other cases, initial minor
slope movement may be a precursor for accel-
erating movement followed by collapse of the
slope. Because of the unpredictability of slope
behavior, movement monitoring programs can
be of value in managing slope hazards, and they
provide information that is useful for the design
of remedial work.
Slope movement is most common in open
pit mines, and many mines continue to operate
safely for years with moving slopes that are care-
fully monitored to warn of deteriorating stability
conditions. Other slopes that undergo long-term
movement are landslides that may creep for hun-
dreds of years resulting in accumulative move-
ment of tens of meters. Such movement may
comprise an approximately uniform creep rate,
on which may be superimposed short periods of
more rapid movement resulting from such events
as earthquakes, unusually high precipitation peri-
ods and human activities. Human activities that
can be detrimental to slope stability include
excavations of the base, and changing the ground
water conditions by dam filling or irrigation.
This chapter describes common methods of
monitoring movement of rock slopes, and inter-
pretation of the results.
monitoring programs are most appropriate for
actively mined slopes such as open pit mines
and quarries which have a limited operational
life and where a carefully managed, on-going
survey operation can be set up. The survey will
be able to identify accelerating movement of the
slope and take measures to minimize the risk by
moving operations away from the active slide.
Figure 13.1 shows an example of an open pit slope
where careful monitoring identified the increas-
ing rate of movement, which allowed the actual
collapse to be photographed. There are several
well-documented cases of slope monitoring at
open pits where mining continued for several
months below the moving slope. Eventually the
rate of movement increased rapidly indicating
that stability conditions were deteriorating and
operations were halted shortly before the slope
failed (Kennedy and Neimeyer, 1970; Brawner
et al
., 1975; Wyllie and Munn, 1979; Broadbent
and Zavodni, 1982).
Monitoring may also be suitable for large land-
slides that threaten facilities such as reservoirs,
transportation systems and residential areas. The
weaknesses of such programs are that they may
have to be maintained for long periods and may
involve sophisticated monitoring and telemetry,
which will be costly. Also, it may be difficult to
identify deteriorating stability conditions that will
clearly show there is a need to evacuate the site. It
is considered that where there is a significant risk
to lives and property, remediation is preferred to
long-term monitoring.
It is considered that
