4
or shortly after active mining. Although there had been on-
going material degradation inherent to exposure, it had not
induced significant, observable slope movement.
Another local observation was that there were no
“large” rocks that have accumulated on these benches. This
does not mean that there is never a risk for rockfall in the
future. It simply indicated that the rock mass tends to break
into smaller rocks/fragments. Overall, when this assessment
was completed, the pit slope within which the proposed
portal would be located, had performed very well, with no
obvious signs of instability.
ROCKFALL ANALYSIS
A rockfall study was conducted using Trajec3D. The high-
wall geometry was developed from recent laser scan survey
data to build a detailed surface on 1-ft contour inter-
vals. The survey data was smoothed to filter collinear and
duplicate points, to reduce the number of triangulations
to a quantity that could be imported into Trajec3D. The
remaining properties are summarized in the Table 1.
The rockfall initiation points were manually selected.
In the case of this analysis, 500 initiation points were
selected across the open pit slope in the proposed portal
area. Since the material that composes the highwall tends
deteriorate into small fragments, or small rocks, the mini-
mum allowable rock size permitted in the software at the
time, 220-lbs, was determined to be representative of typi-
cal rockfall events.
Figure 5. A closer view of the highwall above the proposed
portal location
Figure 6. A view looking parallel to the highwall and catch
benches above the proposed portal location
Figure 7. A July 2010, photograph that shows the upper
benches of the highwall above the proposed portal location
Figure 8. This January 2011 photograph shows the highwall
above the proposed portal location. Development of the
existing portals has commenced in the northern end of the pit.
Table 1. Slope material properties
or shortly after active mining. Although there had been on-
going material degradation inherent to exposure, it had not
induced significant, observable slope movement.
Another local observation was that there were no
“large” rocks that have accumulated on these benches. This
does not mean that there is never a risk for rockfall in the
future. It simply indicated that the rock mass tends to break
into smaller rocks/fragments. Overall, when this assessment
was completed, the pit slope within which the proposed
portal would be located, had performed very well, with no
obvious signs of instability.
ROCKFALL ANALYSIS
A rockfall study was conducted using Trajec3D. The high-
wall geometry was developed from recent laser scan survey
data to build a detailed surface on 1-ft contour inter-
vals. The survey data was smoothed to filter collinear and
duplicate points, to reduce the number of triangulations
to a quantity that could be imported into Trajec3D. The
remaining properties are summarized in the Table 1.
The rockfall initiation points were manually selected.
In the case of this analysis, 500 initiation points were
selected across the open pit slope in the proposed portal
area. Since the material that composes the highwall tends
deteriorate into small fragments, or small rocks, the mini-
mum allowable rock size permitted in the software at the
time, 220-lbs, was determined to be representative of typi-
cal rockfall events.
Figure 5. A closer view of the highwall above the proposed
portal location
Figure 6. A view looking parallel to the highwall and catch
benches above the proposed portal location
Figure 7. A July 2010, photograph that shows the upper
benches of the highwall above the proposed portal location
Figure 8. This January 2011 photograph shows the highwall
above the proposed portal location. Development of the
existing portals has commenced in the northern end of the pit.
Table 1. Slope material properties