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| Titel |
Subaqueous landslides in earthquake-prone South-Central Chile: The role of ash and quick clay on slope failure |
| VerfasserIn |
Gauvain Wiemer, Jasper Meornaut, Nina Stark, Phillipe Kempf, Marc De Batist, Mario Pino, Roberto Urrutia, Michi Strasser, Achim Kopf |
| Konferenz |
EGU General Assembly 2013
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 15 (2013) |
| Datensatznummer |
250078538
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| Zusammenfassung |
| Submarine slope failures represent one of the most frequent, dynamic and devastating
geohazards along active margins concerning onshore and offshore infrastructure as well as
coastal communities. ’In situ’ geotechnical characterization of submarine slopes located in
active geological settings is therefore compulsory for the understanding of submarine
landslide initiation. Lakes have been shown to represent “small-scale model oceans”
with a regionally constrained area where most of the governing factors are known.
Other than in the marine realm, sliding surfaces, i.e. ’weak layers’ are easily and
cost effectively accessible with conventional coring rigs and ’in situ’ geotechnical
devices. Lake Villarrica is such a natural laboratory for landslide initiation studies
in a seismically and volcanically active area. It is a large glacigenic lake (ca. 20
x 10 km) located at the foot of Villarrica Volcano in the Andes, in south-central
Chile. High magnitude earthquakes occur regularly due to the subduction of the
Nazca plate under the South American continent. Seismic reflection and side scan
sonar data of this lake reveal numerous slope failures characterized by two main
sliding surfaces at two distinct levels in the stratigraphy. The MARUM free fall
shallow-water CPT has been deployed in order to investigate the geotechnical properties of
these lithological units. Cone resistance, sleeve friction and pore pressure have
been measured on a plateau of unfailed slope material down to a depth of ~ 8.1 m,
reaching both stratigraphic units that act as sliding surface on the slope. Cores of ~
8 m length have been taken for further geotechnical laboratory experiments and
sediment characterization. The upper ~7 m of unfailed sediment mainly consist of
biogenic opal alternating with tephra layers. The lower part of the core contains
quick clay with a sensitivity > 500. At ~ 3 m depth a drastic decrease in cone
resistance gradient has been noted. One of the sliding surfaces is located right above a
sandy-silt tephra layer that is susceptible to liquefy as confirmed by cyclic triaxial tests.
The second sliding surface is located within the unit of quick clay. None of the
sliding surfaces has been identified as being particularly weak in terms of static
drained shear strength. However, the undrained shear strength deduced from cone
resistances data indicate an overall overconsolidation of the sediment except the quick
clay.
We present a broad set of ’in situ’ and laboratory geotechnical data (CPT, MSCL, SEM,
XRD grain-size distribution, moisture and density, vane shear, direct shear, cyclic triaxial
shear) that characterize the sliding surfaces of a subaqueous slide in much detail. This data
set, combined with seismic and side scan data of sediment involved in large lake-bottom
sliding processes, allows for detailed location and analysis of a ’weak layer’ and contributes
to a better understanding of slope failure initiation applicable to the marine realm. |
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