Civil Engineering Reference
In-Depth Information
empirical approaches to be applied in design.
However, limitations may exist in being able to
predict, adequately, initial slope performance.
Consequently, early mining phases may require
conservative slope angles to provide experience
from which future slope performance can be
assessed. Once experience is gained, determ-
inistic, probabilistic, empirical and numerical
modeling assessments can be calibrated against
slope performance, allowing ultimate pit slope
designs to be optimized.
Deep-seated deformation can result in slope
movements of tens of meters per year. There-
fore, a comprehensive slope movement monit-
oring system is required to provide advanced
warning of increased slope movement rates. This
typically includes a network of reflective survey
prisms, wire extensometers and borehole inclino-
meters in critical areas. Contingency planning is
also required to build flexibility into the mine
designs, such that mitigation measures can be
implemented to remediate areas of instability, if
necessary.
Depending
infrastructure and the flexibility of the mine plan
(i.e. single versus dual, or multiple, ramp access),
deformation analysis using a discontinuum mod-
eling approach such as UDEC (see Chapter 10)
may be carried out. Deformation analysis requires
a high level of understanding of the slope deform-
ation controls, as well as detailed slope mon-
itoring and ground water information. With
adequate calibration, these models can provide
predictions of possible slope behavior, allow-
ing movement threshold criteria and contingency
plans to be developed.
15.4.2 Engineering geology
The engineering geology of the slope is shown
on the cross-section in Figure 15.10. The geo-
logy was based on detailed pit mapping and
core logging, and the structural geology inter-
pretation was based on oriented core drilling
and projections of structural mapping from the
existing pit.
A 50 m wide regional fault zone dipped at
approximately 80
â—¦
into the lower pit slope, with
a strike approximately parallel to the slope face.
on
the
critical
nature
of
the
pit
slopes,
the
location
of
important
mine
Hanging
Wall
Shear
Zone
Footwall
Interim pit
Ultimate pit
Piezometer
Interim pit
water table
Structural
fabric
Pumping
well
Ultimate pit
water table
Sub-horizontal
drain hole
Major
fault
Major fault
zone
Figure 15.10
Example 4—engineering geology cross-section of open pit slope prone to deep-seated
deformation.
