Geoscience Reference
In-Depth Information
Figure 5.18, which displays many different nature tests, may be complex.
Nevertheless, it is perfectly representative of the investigative methods adopted by
Biarez, who, through an experimental approach, sought to arrive at an
all-encompassing logical system of explaining the behavior of granular materials
(with or without glue).
In this figure, we find a number of standard reference lines, the ISL, the CSL, the
Castro SSL, the two frontier lines UF and UL of Flavigny, and the Ishihara SSL
curve (Figure 5.18).
Four outstanding undrained tests (thick dotted line) permit the CSL for the lump-
less sands to be located: two Lee and Seed tests [LEE 67] with
e
0
= 0.78 and
e
0
= 0.83 (denoted
Seed 0.3
and
Seed 3
), the Flavigny and Bousquet test 10, with
e
0
= 0.93 (denoted
Bous 1
), and a test by Benhamed [BEN 01] with
e
0
= 0.93
(denoted
Nad 0.1
).
We remark that the lump tests reach the SSL (
Nad 0
), but at times they return to
it after going beyond it (
Meg 17, 24, 34
). Certain tests, before or after reaching the
SSL, return to the CSL (
Meg 6, 37, 36
).
Most of the tests, stopped at 20% for axial strain, were not strictly speaking
“liquefied”; so the deviator might have slightly moved upwards to produce what
could be called an attempt to “reach the perfect plasticity stage” (as a return to
CSL
).
Thus, the question of a possible return of the lumpy sands towards CSL seems to be
an open affair. We could attribute the abrupt fall towards zero of certain tests in the
literature to a phenomenon of large strain localization. Nevertheless, to continue
running a test beyond 20% in strain without finding localization would, according to
Biarez, be the equivalent of a technical miracle.
Finally, Biarez asked to draw two other lump type tests in this plane:
- the drained tests of Al Mahmoud [ALM 97], which tend towards the Castro
SSL into the Flavigny gap UF-UL that, with regard to the SSL, have normally
consolidated and overconsolidated behavior;
- the Meghachou tests, with
p'
constant, (
PC1, PC2, PC4
and
PC5
), which tend
towards the SSL.
It was with the utmost care that Biarez verified the current models (lump sands
moving towards the SSL line), even if the tests did not accord with his new
hypothesis (a return to the CSL). His approach was experimental, his observational
method meticulously elaborate and guided by a fundamental intuition of the physics
of granular materials.
Search WWH ::
Custom Search