Civil Engineering Reference
In-Depth Information
W
E
1H
H-III
F-I
3F
Pit
H-II
H-I
F-II
2F
F-III
F-IV
2F
F-II
Symbols
3F
Slope design concept
H-III
Legend
Design sector boundary
Jurassic shale/mudstone (Domain 1)
Undifferentiated
sediments
Cretaceous
(Domain 2)
Sandstone
Coal measures, Cretaceous (Domain 3)
Figure 15.9
Example 2—slope design concepts applied to typical geologic cross-section (modified after Hawley
and Stewart (1986)).
with a near-vertical regional fault or shear zone,
exposed in the lower portion of one of the pit
walls, that defines a boundary to the ore body.
Overall, these rock masses are variably
altered, structurally complex and exhibit high
ground water pressures. Slope depressurization is
difficult due to structural compartmentalization
of ground water and low rock mass conductivity.
15.4 Example 3—deep-seated deformation
in a weak rock mass
Weak rock mass conditions can occur in many
types of ore deposits, especially where ore depos-
ition is associated with alteration or complex
structural zones. The lithologies associated with
these conditions can be considered to represent a
wide range of geological environments including:
(i) highly fractured plutonic rocks (e.g. copper
porphyry deposits); (ii) metasedimentary or meta-
volcanic rocks (e.g. shear hosted gold deposits);
or (iii) mafic volcanic rocks (e.g. asbestos depo-
sits). This example is a generalized case history
of combined experience at four operating mines
with open pit slopes ranging from 300 to 500 m
high. The main similarity between these projects
is the presence of a weak rock mass associated
15.4.1 Design and operational issues
Large-scale pit slopes may be prone to deep-
seated deformation due to stress concentrations
in the highly deformable weak rock mass in the
toe of the slope, or complex modes of failure
such as squeezing or toppling extending to a
considerable depth behind the face. These con-
ditions often require a number of analytical and
