Environmental Engineering Reference
In-Depth Information
were affected by a variety of rock falls and slides.
specific fieldwork methods were necessary for an
effective characterization of rocks and to deter-
mine the most convenient stabilization techniques.
2
case sTUDies
2.1 Los Teques apartments and slope, Southern
Gran Canaria Is.
in December 2005 a 11.6 metric ton rock block fell
down on the back corridor of the apartments and
the structure of the building was damaged. For
some days, other smaller rock falls occurred. after-
wards, by means of a detailed geological study of
the whole slope, 105 m long and 30 m high, 9 zones
of medium to high risk were found out. in the study
there were considered the strength and weathering
of the rocks, potential rock fall mechanisms and
trajectories, and the superficial and underground
waters influence.
in addition, many specific solutions were pro-
posed for the slope stabilization. Five building
companies were consulted and some of them pro-
posed more general and expensive stabilization
methods than required. Finally, a variety of tech-
niques were used (rock bolts, cable nets and dowels,
concrete walls, shotcrete, cable belts, cable barriers,
etc.) which were applied on specific areas.
Fieldwork was focused on three main targets:
(1) Geological characterization of rocks and soils;
(2) identification of unstable rock blocks and loose
debris, and (3) definition of the best construction
methods to retain or avoid potential rock falls, tak-
ing also in account the cost and effectiveness of
each method.
The geological materials of the slope are of
three main types: (a) acid volcanic agglomerate
of fragments with ash and pumice which is a soft
rock also affected by a fresh water spring; (b) 2 to
3 lava flow layers, which are ignimbrite of medium
to high strength, and (c) some superficial scree and
debris deposits. all rocks are of trachyte-rhyolite
composition and they correspond to the Miocene
magmatic cycle of Gran canaria is.
The volcanic agglomerate outcrops at the base of
the slope, just behind the apartments, with a thick-
ness of 10-15 m. its high slope angle (70-80ยบ) and
weathering had caused the undermining of the upper
lava flow layers, which are 15-20 m thick. These lay-
ers had a number of unstable rock blocks with var-
ied (wedge-, columnar-, cubic-) forms ( Fig. 3 ) .
When the unstable zones had been identified,
one by one, a rock fall hazard map was done, con-
sidering three categories of risk: low, medium and
high. construction solutions were mainly focused
on the stabilization of medium and high risk zones
( Fig. 4 ).
Figure 2. General view of los Teques apartments and
rocky slope in southern Gran canaria island.
Figure 3. Removal of the 11.6 tons rock block that fell
down at the back of the building. Damages caused by
this rock fall.
Figure 4. Risk map of los Teques slope. stabilization
methods were focus on medium to high risk zones.
To evaluate the cost of construction works
which were needed for the slope stabilization five
building companies were consulted and some of
them proposed more general and expensive stabili-
zation methods than required. Finally, a variety of
techniques were used ( Fig. 5 ) :
 
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