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Research & development

From the front slope towards

the interior of the slab, the rock

fracturing condition becomes less

intense, with spacing ranging from

less than 1m up to more than 2m

or more. This may be appreciated

both in the plateaux above the cliffs

and within the several quarries

opened inside it. Nevertheless, in

the inner part of the west side of

Cala Rossa cliff, upon the plateaux

and approximately 25 meters from

FIGURE 5 The local GPS network and one of the measurement points the edge,two major discontinuities

have been recognized, longer than

The GPS network is composed by four stable vertices (A, 100 meters, 50 cm open and with 40 cm of offset. These

B, C and D in Figure 5), while in proximity of the edge of joints seem to reach the contact with the underlying

the cliffs four sites were chosen, considered potentially clays, isolating a huge block of approximatively 30

unstable after a geomorphological survey (E1, E2, O1 thousand m3 (Figure 6).

and O2). The GPS network was linked with the Italian Structural analysis confirms the presence of two main

Geodetic Network (IGM95), by the geodetic point joint families:NNW-SSE and NE-SW (Figure 7 and 8).The

“Punta San Leonardo” located close to the Favignana’s NNW-SSE joint set seems to have a significant relevance

urban area. The uncertainty of these vertices was very in the structural asset of the area and in the development

contained, reaching a maximum of +/- 2 mm in plane of the instability proneness. Especially where this joint

and +/- 3 mm vertically. set is parallel to the slope face,it is possible to recognise

an advanced lateral detensioning deformation process.

Results Less significance seems to have the sub-horizontal

stratification planes. Taking into account the attitude of

the main measured joint, two failure mechanisms have

The biocalcarenitic slab shows a high degree of been assumed for the movements in the front part of the

fracturing especially in the front portion of the cliffs cliffs: rock topples and rock wedge slides.

and the boulder deposits at their foot constitute a The results of the geomechanical analysis of the 25

clear indicator of the current activity. Several blocks stations, implemented in the GIS project, are showed in

of different sizes seems to be in condition of high the rock quality maps (RMR, SMR and SR) that constitute

instability and in proximity of falling. In addition a preliminary assessment of the rock fall susceptibility of

to the geomorphological indicators, at least two

block fall events recorded during the 24 months of

the study testify the high activity of the west cliff of

Cala Rossa. The first is the block of approximately

0.3m3 collapsed on the morning of October 26, 2012

from the west cliff of Cala Rossa and recorded by the

Laser Scanner monitoring. The second is the sudden

collapse of a boulder on which a reference pin for

the removable joint-meter measuring was installed.

Its last data read in June 2013 indicated a movement

of 0,72mm from the installation in October 2012

(1mm/month). FIGURE 6 Giant joint of Cala Rossa

64 EAI Energia, Ambiente e Innovazione 4/2015