Cliff stabilization solutions at the south coast of Madeira Island - Volcanic Rock Mechanics - page 180

pool complex and several service buildings were
constructed at the base of the cliff ( Fig. 4 ). The
distance between these infrastructures and the cliff
was between 3 and 10 m.
When the seaport was constructed, stabilization
works consisting on bolted metallic wire meshes
were executed from the base up to elevations 85.00
to 90.00 m, where it essentially presented verti-
cal inclination and was constituted by basalt lava
flows interbeded with breccious levels.
a flexible barrier was placed at a platform
located at these elevations, with the purpose of
retaining any material that might fall from the
upper section of the cliff, which had a less aggra-
vated inclination and consisted of thick layers of
compact tuffs and of basaltic flows. layers of
intercalated volcanic breccias were also identified
within the basaltic flows.

over time it became clear that this barrier did
not provide sufficient protection against rockfall
from the upper section, which led to the interdic-
tion of the parking building, the swimming pool
complex and the service buildings (cenorgeo,
2006b).
hence, a stabilization solution was developed
consisting on the excavation of the upper section,
from the top of the cliff, at elevations 90.00 m to
150.00 m, to the platform located at elevations
85.00 to 90.00 m.
This work was carried out along a length of
about 200 m, along slopes 5V/1h at the base to
10V/1h at the top.
Given the nature of the rock mass, consisting
essentially of tuffs, a shotcrete lining was applied
on the excavated slope along with the execution of
8 to 12 m long bolts.
it is noteworthy that the resulting slope was
designed to guarantee a minimum working plat-
form width of 6 m, to assure a safe circulation of
the equipments.

5.4 Cliff above the ER222 at Sítio do Calvário
This cliff has a length of about 50 m and an
approximate maximum height of 50 m.
it is limited, at the top, by a sub-horizontal
platform at elevation 175.00 m, where a house was
built, and, at the base, by the eR222 road, at eleva-
tion 130.00 m.
it is constituted, at the base, by a first slope
about 15 m height, excavated with a sub-vertical
inclination and it is formed essentially by relatively
compact and resistant breccias that are, neverthe-
less, disaggregatable.
There is a narrow platform on the top of this
slope, about 1 m width, which widens until reach-
ing about 5 m.
overlaying this platform there's another slope,
about 20 m height, also sub-vertical, consisting of
a thick and compact, but fractured, basaltic flow,
where it is possible to observe several polygonal
columns and large rock blocks that could fall in the
short term and affect the road (cenorgeo, 2008b).
The solutions adopted for the stabilization of
this cliff consisted on the removal of all the unsta-
ble rock blocks, open joints sealing and the bolt-
ing of the unstable blocks that were not possible
to remove.
The disaggregated breccias found in the lower
slope, underlying the basaltic bedrock, were pro-
tected with a shotcrete lining ( Fig. 5 ) .
To carry out these works it was necessary to
temporarily close the road, introducing a signifi-
cant impact on the local population.
in order to cut the time of execution of the stabi-
lization works to a minimum and to ensure that the

a. General view of the cliff after the stabilization works

b. cross-section of the upper section of the cliff

Figure 4. cliff above the lugar de Baixo seaport.