Environmental Engineering Reference
In-Depth Information
in this case, the aim was to assure that the final
slope was located behind the unstable surface. That
was accomplished by a continuous topographical
survey during the excavation.
During the excavation, a strip about 2 m wide
and 1 to 2 m high was maintained at the outside
edge of the cliff, as a safety measure to prevent
workers and equipments to fall to the bottom of
the cliff during stabilization works at that level,
being only removed in a secondary phase, when
the works were completed.
5.2
Cliff above the ER222 at Sítio da Vargem
on June 18th 2008 an estimated volume of 350 to
400 m
3
of basaltic blocks fell off the cliff at sítio
da Vargem, onto a section of the eR222 road. This
rockfall completely blocked the road and the access
to an adjacent house.
The unstable mass, about 40 m in length and
40 m in height, was bounded at the top by a set of
terraces used for agricultural purposes, supported
by drystone packed walls.
The cliff was formed, at its base, by a layer of
relatively compact and resistant tuffs, on top of
which occurred disaggregated breccias. Basaltic
flows overlayed these two layers, where several
columns and very large blocks were identified as
unstable. Disaggregated breccias also occurred on
the inside of the cliff, behind the basalts. on top
of this flow, there was yet another level of fairly
compact breccias (cenorgeo, 2008a).
The adopted solution was to progressively exca-
vate the basalts, along a 3V/1h slope, with berms
with a minimum width of 1.5 m and vertically
spaced by 12 m.
The excavation solution appeared to be the most
appropriate solution, based on the survey conducted
on the top of the cliff (shortly after the rockfall)
that allowed the identification of several important
cracks, bounding a possibly failure surface.
a shotcrete lining associated to 6 to 12 m length
bolts was used on the disaggregated breccias and
on the fractured basalts.
The stabilization of the compact basalt blocks and
it is noteworthy that immediately after the rock-
fall an access road to the top of the cliff was created,
to allow the beginning of the stabilization works.
attending to the urgency on resolving this situ-
ation, namely due to inconvenience of the road
interdiction, the works began to be conducted with
a daily monitoring by the design team, which was
permanently adapting the design to the geological
and topographical conditions encountered as the
works were being executed.
it should also be noted that due to the lack of
space, it was not possible to maintain the road
a. General view of the slope after the stabilization
works.
b. cross-section
Figure 3.
cliff above the eR222 at sítio da Vargem.
access along the successive excavation levels, inhib-
iting the circulation of transport vehicles of the
excavated materials for dumping.
Therefore, it was necessary to create a reception
basin on the eR222, through the construction of a
delimiting barrier in its exterior alignment (to pre-
vent the material to overlap the basin), being the
excavated material then carried for dumping using
this road.
For the same reason the equipment that per-
formed all the excavation, could only be removed
after the completion of the stabilization works.
5.3
Upper section of cliff above Lugar de Baixo
Seaport
The lugar de Baixo seaport was constructed at
elevation 4.00 m, at the base of a cliff with about
200 m height. a parking building, a swimming
