Environmental Engineering Reference
In-Depth Information
Given that all tests yield similar values of the void
the shear zone measured at incipient liquefaction in
the test #2 results highly reduced (
e
f
= 0.39). such a
decrease indicates that even though the shear dis-
placement is low, crushing occurs and grains are
strongly rearranged within the shear zone. This
consideration is supported by the low reduction
of void ratio (
e
passed from 0.69 to 0.65) which
was instead experienced by a further test (test #3)
stopped fairly before liquefaction (not described
in the previous sections). liquefaction at higher
displacements (test #5) does not induce a further
reduction of void ratio.
The shift of grain size curve of tests #2
are appreciable. an identical curve was obtained
in the stress-controlled test #3, carried out with
open drainages. The grain size reduction is quite
higher in the specimen of test #5, which attains
liquefaction (limited or local) at larger shear
displacements.
The larger influence that liquefaction conditions
have on the void ratio induces two considerations:
i) at relatively low displacements grain crushing
seems to manifest itself as ruptures at grain sur-
faces, which improve particle packing; ii) void
ratio well before liquefaction experiences moderate
changes due to shearing.
The measurements of void ratio during large-
displacement tests conducted with open drainages
suggest that a critical void ratio (at steady state
conditions) can be individuated and that it depends
on the initial void ratio. This indication could be
useful for establishing, in the case of crushable
soils, the ultimate resistance of the material. in this
respect the increment of total displacement from
20 to 30 m (curves “inner shear zone Test 6” and
grain size distribution within the inner part of the
shear zone.
acknoWleDGeMenTs
authors thank e. Tempesta, P. Millozzi and
l. Passeri of cnR-iGaG and eng. G. caldarini
for sample preparation.
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