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Dispersion of the strength values, both compres-
sive and tensile, is minimal for the case of maxi-
mum alteration grade. This seems reasonable if we
consider that the porosity increases but generally by
minor pore sizes and so excluding large imperfec-
tions and weaknesses that instead are more frequent
at lower alteration grades (see companion paper).
The progressive increase in the P wave velocity
that has been observed for some of the samples could
be associated to the progressive compaction of the
sample with a slight decrease in pore volumes.
Finally, Figure 6 shows the general trend fol-
lowed by the various physical mechanical proper-
ties as a function of the pore size fractal dimension
determined by Micro cT image analyses (see com-
panion paper). in general, an increase in the values
of compressive and tensile strength is observed for
increasing fractal dimensions.
This trend is inverted for high fractal dimen-
sion values that in our case are relative to the more
alterated grade (5). This is probably the result of an
increase in frequency of small pores with respect
to large ones (see increase in total porosity in
fig-
a decrease in strength of the material due to argili-
zation and silicization, and precipitation of amor-
phous minerals within large preexisting pores.
This study confirms the exceptional role played
by alteration in degrading mechanical properties
of volcanic rocks. as a consequence, this suggests
that a correct and complete physical-mechanical
modeling is required when stability problems
involving volcanic and highly altered/weathered
rocks are performed.
Presently, a more complete physical-mechanical
characterization is under way for the described
lithology so to develop a more complete geome-
chanical constitutive model to be introduced in
numerical models. in particular, triaxial tests,
isotropic compression and soft oedometer tests are
currently being performed.
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Figure 6. General trend observed for the change of the
physical mechanical properties with the average fractal
dimension as evaluated by porosity values determined by
Micro cT analyses (see companion paper).