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Discussion
The geological model representative of the study area
is mainly characterized by the presence of the rigid
body of calcarenite above the plastic clays. The clay
deformations, also related with the sea waves action,
induce stress condition in the overlying limestones
and development of fracturing processes. The pre-
existing neo-tectonic shear zones are a controlling
factor for the development of the failure surfaces
and of the gravitational processes. These processes
develop as lateral spreading along the contact
surface between the two formations and fall s.l. in the
detensioned front portion of the cliffs. The position of
the contact surface between the two formations above
or below sea level and the consequent exposition or
protection of the clays to/from the sea waves action is
presumably a further controlling factor for fracturing
and landslide processes.
The lack of significant movement registered by
the integrated monitoring system in the periodic
acquisition during the 24 months study can be easily
explained with the discontinuous and impulsive
behaviour of the rock collapsing processes, and does
not exclude the possibility of future single or massive
movements. The deepening of the deformation
dynamic inevitably requires the upgrading of the
current monitoring network with the installation of
more sophisticated joint meters in the most critical
sites, with in continuum acquisition, data logging and
remote communication.
The rock mass rating of the cliffs attributed to the different Cala Rossa, a partial prohibition of access is strongly
measuring stations (Figure 9) shows good agreement
between the SMR and SR classifications, even if the
latter appears to be more conservative. It is notable that
attributing the SMR and SR classes demands to take into
account the geometrical relationship between the most
significant joint planes and the slope orientation. Even
though the analysed cliffs of three bays have strongly
indented forms, due to natural and human causes, in
this study only an average value of the slope orientation
has been used. Consequently, the SMR and SR classes
assigned to a station are affected by a certain level of
approximation.
The working group plans to make few more additional
field observations and deepen the elaboration of
the data already acquired. An improvement of the Research & development
landslide hazard assessment will be implemented
on the basis of the predisposing parameters, such
as the stability condition of the slopes [20, 21]. The
characterization of the joint discontinuities will
strengthen by the execution of the automatic and semi-
automatic elaborations of the Laser Scanner images
and of an innovative geophysical survey (nanoseismic
monitoring) [22].
Conclusions
The geomechanical survey and analysis confirm
the presence of potential instability conditions in
the three bays of the study area. Consequently, a
significant hazard level has been recognised in
several measurement stations, mainly in Cala Rossa
and Cala del Bue Marino. The monitoring systems
have registered no significant displacements in the
observed areas. Nevertheless, several cliff areas
show evidence of impulsive dynamics. On this basis,
identifying appropriate actions is absolutely crucial
to prevent accidents to the users of these beautiful
natural places and to avoid that the most significant
quarries are further abandoned to an inexorable
degradation process.
Removal of the most unstable blocks, local rock nailing
and protection boulder walls at the foot of the cliffs are
all interventions that can reduce the general unstable
conditions in the higher hazard level sectors of the
cliffs. In the most critical areas, as the west side of
recommended. Furthermore, improving the current
monitoring system is a necessary prerequisite for
future adoption of an early warning system.
By providing information about the hazard level and
the displacements along the cliffs of the three bays,
the present study results are an effective contribution
to the local authorities in charge of implementing
mitigation measures. The enhancement of the safety
level of these areas is an essential step for a sustainable
and safety tourism exploitation in the island. This is the
way to ensure that what was left of the quarries can
become an economic resource again, while respecting
the historical and the environmental context.
67EAI Energia, Ambiente e Innovazione 4/2015