Geoscience Reference
In-Depth Information
electron microscope (SEM) are shown in Figure 6.10. The grains seem to be made
of several assembled layers that are several micrometers thick. This fabric, which is
the characteristic of a residual soil and similar enough to that of a clay, gives a liquid
limit of nearly 33% and a few original properties, especially with respect to
saturation.
Drying-wetting tests were carried out on specimens compacted to the modified
Proctor optimum water content and close to maximum density with tensiometric
plates and osmotic devices. Details of the experimental techniques are given, for
instance, in [BIA 88] or [VER 02]. The drying and wetting paths starting from the
compaction point are shown in Figure 6.11, in the void ratio and water content
versus capillary pressure planes, respectively. When the soil is normally
consolidated or slightly overconsolidated, these paths exhibit hysteresis [FLE 93];
whereas for a soil compacted under these conditions, the paths are generally
reversible [FLE 02b]. The points corresponding to the specimens prepared for the
large strain triaxial tests, i.e. compacted to different water contents and densities,
were also plotted on the graph. These points are not located near the drying-wetting
paths and cannot, therefore, be used to estimate the capillary pressure of compacted
specimens.
6.3.2. Experimental devices and test procedures
The modules were measured by means of two different triaxial cells with local
strain measurements, one (called LPTT, large cell for precision Triaxial tests) at the
Instituto Superior Técnico (IST) in Lisbon for the tests on large specimens and the
other one (SPTT, small cell for precision Triaxial tests) at the Ecole Centrale de
Paris (ECP) for the tests on smaller specimens. Capillary pressure measurements
were carried out at ECP in a conventional triaxial cell (TTu, Triaxial tests with
control of suction) equipped with a semi-permeable porous stone and an absolute
pressure transducer.
w L
%
w P
%
I P
%
< 2µm
%
< 80µm
%
w opt
%
γ dmax
kN/m 3
G s
M pp
Standard:
17.6
Modified:
13.2
Standard:
16.8
Modified:
18.6
32.6 25.0
7.6
2.5
20
2.66 1.1
Table 6.2. Geotechnical properties of Perafita silty sand
 
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