Environmental Engineering Reference
In-Depth Information
shear behaviour of stromboli volcaniclastic saturated materials
and its influence on submarine landslides
P. Tommasi
Institute for Geo-Engineering and Environmental Geology, National Research Council, Rome, Italy
F. Wang
Research Centre on Landslides, Disaster Prevention Research Institute, Kyoto University, Kyoto, Japan
D. Boldini
Department of Civil, Environmental and Material Engineering, University of Bologna, Bologna, Italy
T. Rotonda & a. amati
Department of Structural and Geotechnical Engineering, Sapienza University, Rome, Italy
aBsTRacT: on 30 December 2002 a submarine landslide generated high tsunami waves and
destabilized the subaerial slope of the nW flank of the stromboli volcanic island. The volcano flank
is a large subaerial and subaqueous scar filled by loose volcaniclastic materials. Their susceptibility to
undrained shear failure is investigated through stress- and displacement-controlled large-scale ring shear
tests (lRsT), conducted at DPRi-kyoto University at different hydraulic boundary conditions. Results
are presented in the form of stress paths and time-histories of shear resistance and pore pressures and are
discussed with reference to the different teting conditions. Finally shear band formed in lRsT are ana-
lyzed in terms of changes in porosity and grain size distribution in order to investigate the development
of grain crushing at failure and at large displacement.
1
inTRoDUcTion
accelerated a couple of hours before the submarine
failure.
The nW flank of the stromboli island is a large
sector collapse scar (more than 200 m deep), filled
by the products of the continuous explosive activity
of the volcano, which are incessantly re-mobilized
by slides over the whole subaerial and submarine
slope. This process forms a sequence of volcani-
clastic layers with interspersed blocks and thin
lava flows. Volcaniclastic layers are predominant
and have large continuity over the submerged and
subaerial slope thus controlling the mechanical
behaviour of the whole deposit.
in order to individuate mechanisms governing
a sudden submarine failure, investigations were
focused on the behaviour of the volcaniclastic satu-
rated material. The large initial dimensions of grains
and the strong dependence of grain size distribu-
tion and void ratio from strain magnitude due to
grain crushing, have addressed experimental activ-
ity towards tests that involve large specimens and
encompass a wide range of strains/displacements.
in this respect a first series of large scale ring
shear tests were performed with the scope of assess-
ing the susceptibility of volcaniclastic material to
in subaerial volcanic edifices, large flank instabilities
occur essentially in the form of sector collapses
(McGuire 1996), which in many cases are directly
driven by volcanic activity through stress changes
induced by magma intrusions or/and fluid pressuri-
zation (Voight & elsworth 1997).
More subtle instability phenomena may occur
on the submerged part of volcano flanks formed by
loose volcaniclastic deposits. in fact the resistance
of the saturated deposit can drops if it is subjected
to loading or deformations as fast as to establish
undrained conditions. This circumstance can occur
if porosity and grain size changes accompany the
shear process as a consequence of grain crushing.
high deformation/loading rates are believed to
have been experienced by the submerged part of
the nW flank of the stromboli Volcano (sicily,
italy) during the 2002-2003 eruption, when a rapid
submarine failure, 6 × 10
6
m
3
in volume, produced
tsunami waves that run up the inhabited coasts of
the stromboli island (chiocci
et al
. 2008). Failure
was preceded by deformations of the subaerial and
of the nearshore submerged slope, which sharply
