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| Titel |
Weathering effects on the mechanical behavior of calcarenites: experimental evidences and impact on the stability of costal cliffs and cavities |
| VerfasserIn |
Riccardo Castellanza, Matteo Ciantia, Claudio di Prisco, Federico Agliardi, Giovanni Crosta |
| Konferenz |
EGU General Assembly 2011
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 13 (2011) |
| Datensatznummer |
250057543
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| Zusammenfassung |
| Long sectors of the Apulian coast (SE Italy) are formed by steep rocky cliffs in fractured and
weathered carbonate soft rocks (e.g. calcarenite and Bari Limestone). These weak/soft rocks,
especially the calcarenite, are strongly affected by weathering processes that markedly reduce
the mechanical properties with time. As a consequence, cliffs and underground cavities are
affected by intense erosion and instability.
In the present work we present the results of an experimental campaign aimed to define
the main weathering processes that affect the soft and porous Plio-Pleistocenic calcarenites
formed by the weak cementation of calcareous grains originally unbounded. The grains of
heterogeneous origin are microscopic fragments of calcareous shells. Diagenetic processes
transform this material in a rock similar to a coarse cemented sand where both grains and
bonds are calcitic (98% of CaCO3) with an average porosity of about 0.52 and an average
pore size dimension of about 0.10 mm.
We carried out a series of laboratory tests including: uniaxial compressive tests, indirect
tensile tests, soft oedometer tests and triaxial tests. Creep tests under controlled “weathering”
conditions were appositely designed by applying a constant load and a controlled water flux
on the sample.
The field and experimental results show three main weathering controlled behaviors:
a) a marked and instantaneous strength reduction, up to 50% of the dry initial value (UCS
1.5 MPa), when increasing the degree of saturation to 1;
b) a slow strength reduction induced by the progressive chemical de-bonding as a
consequence of dissolution reactions; this process has been studied by exposing the
calcarenite to different environmental conditions simulated by a flux of distilled water, acid
solution or saline water;
c) a physical-mechanical erosion by marine wave actions.
The main geomechanical aspects of these processes have been studied and are
presented, and discussed in detail at a micro-structure and micro-fabric scale (bonds and
grains). Observations by SEM, thin sections and X ray CT analyses substantiate the
interpretation of the controlling physical chemical processes. As a consequence, in
order to assess and eventually predict the stability of costal sites and underground
cavities, all the involved weathering processes and their degree of coupling should be
recognized and considered in the modeling phase. A coupled chemo-mechanical
approach is proposed for the geomechanical modeling starting from the experimental
evidences. Preliminary results of small scale boundary value problems suggest
that this approach allow a more reliable risk analysis for large scale instabilities. |
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