Civil Engineering Reference
In-Depth Information
(a)
(b)
Figure 1.1
Examples of rock slopes: (a) rock slope in Hong Kong supported with tensioned rock anchors and
reinforced concrete reaction blocks, and shotcrete (photograph by Gary Fu); and (b) 830 m deep Palabora
open pit copper mine, South Africa. (Photograph courtesy: Rio Tinto Ltd.)
in the range of 1.2-1.4, and it is accepted that
movement of the slope and possibly some partial
slope failures will occur during the life of the
mine. In fact, an optimum slope design is one that
fails soon after the end of operations.
In the design of cut slopes, there is usually little
flexibility to adjust the orientation of the slope
to suit the geological conditions encountered in
the excavation. For example, in the design of
a highway, the alignment is primarily governed
by such factors as available right-of-way, grades
and vertical and horizontal curvature. Therefore,
the slope design must accommodate the partic-
ular geological conditions that are encountered
along the highway. Circumstances where geo-
logical conditions may dictate modifications to
the slope design include the need for relocation
where the alignment intersects a major landslide
that could be activated by construction. With
respect to open pit slope design, the pit must
obviously be located on the ore body, and the
design must accommodate the geological con-
ditions that exist within the area of the pit.
This may require different slope designs around
the pit.
The common design requirement for rock cuts
is to determine the maximum safe cut face angle
compatible with the planned maximum height.
The design process is a trade-off between stabil-
ity and economics. That is, steep cuts are usually
less expensive to construct than flat cuts because
there is less volume of excavated rock, less acquis-
ition of right-of-way and smaller cut face areas.
However, with steep slopes it may be necessary
to install extensive stabilization measures such as
rock bolts and shotcrete in order to minimize both
the risk of overall slope instability and rock falls
during the operational life of the project.
1.1.1 Scope of topic
The design of rock cuts involves the collection of
geotechnical data, the use of appropriate design
methods, and the implementation of excavation
methods and stabilization/protection measures
suitable for the particular site conditions. In order
to address all these issues, the topic is divided
into three distinct sections that cover respect-
ively design data, design methods and excav-
ation/support procedures. Details of the main
topics covered in each section are as follows:
(a)
Design data
•
Geological data
of which structural geo-
logy is usually the most important. This
information includes the orientation of
