Civil Engineering Reference
In-Depth Information
Figure 14.17
Toppling failure in Case
Study V. Sketch showing extent of upper
toppling block removed by blasting, and
location of rock bolts in lower slope.
Figure 9.7. That is, the tall, upper slabs toppled
and caused the lower, shorter slabs to slide. Pos-
sible stabilization options for these conditions
included reducing the height of the toppling slabs
so that the center of gravity lay inside the base,
or installing a support force in the sliding slabs
at the base. These two measures were adopted,
with the combined effect of reducing the tend-
ency for the upper slabs to topple, and preventing
movement of the lower slabs.
included the removal of all trees growing in
open cracks in the rock because these had con-
tributed to the loosening of the blocks of rock
on the face.
•
A row of bolts was installed through one of
the lower slabs. This work was done prior to
excavation at the crest in order to prevent any
further movement due to blasting vibrations.
•
Blasting was used to remove the upper 6 m of
the top slab. The blasting was carried out in
stages in order to limit blast vibrations in the
lower slope and allow additional bolts to be
installed if further movement occurred. The
blasting pattern comprised 6 m long holes on
about 0.6 m centers, with three rows being
detonated on each blast. A light explosive
charge of 0.4 kg/m
3
was used, with spacers
between the sticks of explosive in the blast
holes.
14.6.6 Stabilization method
The following three stabilization measures were
undertaken to reduce the rock fall hazard and to
improve the long-term stability of the slope:
•
Scaling was carried out on the face above
the railway to remove loose rock. This work
