316
Proceedings of the 18
th
International Conference on Soil Mechanics and Geotechnical Engineering, Paris 2013
Proceedings of the 18
th
International Conference on Soil Mechanics and Geotechnical Engineering, Paris 2013
ies tested, the shear strength envelopes
ress their gratitude to Anglo
Am
e for the authorization to publish the results of
(S1), ARCADIS Chile for the
anulaires secs et
one”. These présentée pour l’obtention du Titre
ale de Paris.
Cam
Lee,
Ver
and the relative densit
obtained are very similar to each other. For average confining
pressures (p’) above 0.5 MPa, a little reduction in the envelope
strength at high pressures, associated to a very reduced crushing
of particles is observed. For this reason, the shear strength
parameters are not modified significantly even for higher
confining pressures.
In the same manner, the drained as well as the undrained
shear strength envelope is not sensitive to the different fines
contents tested, with no significant differences being detected
for the range of fines tested, which varied between 12% and
30%. Notwithstanding the above, by considering the average
values obtained for the undrained shear strength Su, it is
possible to observe a decreasing tendency of the Su as the fines
content is increased.
With the hyperbolic adjustment of the stress – deformation
curves, the evolution of the initial tangent deformation modules
(E
i
) was determined. In drained tests, even when the range of
fines content tested varied between 12% and 30%, a narrow
band of normalized values of E
i
with the confining pressure was
obtained. On the other hand, for the undrained case, a larger
dispersion of results was observed.
The values of G
max
deduced from the triaxial tests at small
deformations and resonant column tests, normalized with the
confining pressure, show that for
’
3
< 0.10 MPa, the results
follow a similar tendency observed by Hardin & Drnevich
(1972) in sands of natural origin. This tendency is not observed
for
’
3
> 1 MPa, where the values of G
max
are larger than
expected in the range of densities tested (80< DR(%) <90).
For the fines content tested and confining pressures greater
than 0.1 MPa, the cyclic stress ratio (CSR) are practically
insensible to the fines content. This result differs from what was
observed in tests performed on tailings sands at low pressures,
in which this content significantly affects the required CSR
value (Verdugo, 1983). The effect of the high pressures upon
the CSR value was practically null in three of the four cycloned
sands tested (S1, S2 and S4), and a relative common value was
obtained for all the range of confining pressures applied. In the
S3 cycloned sand sample, the CSR value to induce liquefaction
decreases as the confining pressure increases until 1.5 MPa. For
greater confining pressures, the same CSR obtained with the
other three samples is reached. Due to these results, for
cycloned tailings sands, the consideration of typical factors
K
reported in technical literature may lead to an
underestimation of the CSR value.
The difference observed in the behavior of cycloned tailings
sands with respect to natural sands could be explained due to
the following aspects: the fines of tailing sands have a low
plasticity index and correspond mainly to a “rock flour”
composed by angular and hard particles (the mineralogical
analysis indicated that more than 40% of sand tailings tested is
quartz). Also, a very small amount of particle crushing was
detected at the highest pressures tested, with fines increasing
less than 3% in the grain size distributions post tests with
respect to the initial grain size distribution (Campaña, 2007).
According to this detection, it is possible to anticipate that
tailing sands could have shear resistance (drained and cyclic)
and shear moduli values greater than expected (compared with
natural sand behaviour). A lesser detriment of the drained shear
resistance due to the effects of both high confining pressures
and fines content was observed.
10 ACKNOWLEDGEMENTS
The authors would like to exp
erican Chil
the tests of the Las Tórtolas Sand
permission to access their data base, and to the Ing. Luis
Valenzuela (MSc) for the review of this paper.
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