Environmental Engineering Reference
In-Depth Information
Table 1.
initial (natural) conditions of intact core samples.
Water content
%
Water content at
Rh = 50%
natural density
Mg/m 3
Dry density
Mg/m 3
Degree of
saturation %
sample
Void ratio
nB-4
7.3 to 9.4
11.7
1.31-1.40
1.22-1.28
0.88-0.98
18-26
nB-7
12.3
12.3
1.47
1.31
0.84
35
(around 50%). however, some of the fundamental
tests, specifically the shear strength of the material
“in situ” were determined under saturated or close-
to-saturated conditions. in general the objective of
tests was to evaluate the suitability of the tuff as
a foundation material. Therefore, in addition to
strength, there was an interest in determining the
tuff permeability and its susceptibility to disper-
sion through the pin-hole test.
Table 2.
consistency limits and content of fines (<75 µm).
liquid
limit
Plastic
limit
Plasticity
index
sample
<75 µm
nB-4
56%
45%
11%
53%
nB-7
76%
45%
31%
57%
40
NB-4 (23.6-23.8m)
NB-7 (19.2-19.5m)
2.2 Basic identification
The X-ray diffraction plot was difficult to interpret
because the powdered sample was fundamentally a
mixture of amorphous (i.e. non-crystalline) phases.
The expansive clay mineral montmorillonite was
also identified. in addition, plagioclase (calcium/
sodium feldspar) was distinguished as a minority
phase. The soil investigated displays other crystal-
line phases, which are difficult to identify.
The initial conditions of two intact core sam-
ples tested are summarized in Table 1. The density
of solids was measured on sample nB-4, giving
a value of ρ s = 2.41 Mg/m 3 . The same value was
used on nB-7 to estimate void ratio and degree of
saturation. The relative humidity (Rh) prevailing
at laboratory conditions is around 50%. since core
samples were not properly isolated to prevent water
content changes, the water content was affected by
this condition (especially on sample nB-4).
core samples were crushed for particle size
study and afterwards remoulded for consistency
limit determination. Table 2 summarizes the main
results. Figure 6 shows the consistency limits plot-
ted in the plasticity chart (inorganic silt Mh).
Figure 7 presents the particle size distribution
curves obtained by sieve analysis.
a mercury intrusion porosimetry (MiP) test
provided information on the multiple porosity
network of the intact sample nB-7. This infor-
mation is useful to improve the understanding
of the hydro-mechanical behaviour of the intact
material and to compare the pore network with
that obtained using a compaction procedure. MiP
tests attained maximum intrusion pressures of
220 MPa (entrance pore size of 6 nm according to
Washburn equation). a freeze drying process was
used to dry the samples and to preserve the pore
network before the injection of mercury.
CH
35
30
25
20
CL
15
10
CL
CL - ML
5
ML & OL
MH & OH
ML
0
0 0 0 0 0 0 0 0 0 0 0
Liquid limit, w L (%)
0
Figure 6.
consistency limits plotted in the plasticity
chart.
ASTM:
#4
#
1
#
1
6
#40
#100
#200
100
80
60
40
20
NB-4 (23.6-23.8m)
NB-7 (19.2-19.5m)
0
10
1
0.1
0.01
Particle size (mm)
Figure 7.
Particle size distribution.
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