Environmental Engineering Reference
In-Depth Information
NB-4 (23.6-23.8m) (natural state)
peak stress
just after peak
ultimate conditions
1.40
NB-4 (23.6-23.8m)
Standard Proctor
400
1.30
350
300
S
r
=1
250
1.20
200
S
r
=0.8
150
1.10
100
8 2 6 0 4 8 2 6 04
Water content,
w
(%)
4
50
Figure 12.
standard effort compaction curve (nB-4).
0
network formed by large inter-aggregate pores
between aggregations or grains of approximately
3-8 µm, and smaller intra-aggregate pores inside
aggregates or grains between 20-50 nm. although
the compaction at standard effort allowed easily
reaching dry densities similar to the natural con-
dition, it is important to remark that this density
was achieved with dominant macro-pore sizes and
macro-porosity larger than those found for the
fact, a slightly larger water permeability and com-
pressibility on loading and soaking (collapsibility)
of the compacted material compared to the intact
one is expected.
0
50
100
150
200
250
Vertical effective stress,
σ
'
v
(kPa)
Figure 11. shear strength envelopes for different con-
ditions (peak, just after peak and ultimate conditions).
intact core sample nB-4. shear strength parameters.
oedometer cell under loaded conditions (50 mm
diameter and 20 mm high specimen). The vertical
total stress applied was 75 kPa. a water pressure
of 30 kPa was applied at the bottom of the sample
by a GDs instruments advanced pressure/volume
controller with a pressure resolution of 1 kPa and
a volume resolution of 0.5 mm
3
/step. Pressure at
the top of the sample is maintained under atmos-
pheric conditions. The saturated water permeabil-
ity is determined under steady-state conditions.
saturated permeability is low (3.5 × 10
-10
m/s)
(in just one determination). This is a value repre-
sentative of “matrix” conditions. in the absence of
fractures/joints tuff permeability is low. This low
value is significantly lower than some field deter-
minations in boreholes.
The pin-hole test performed identified a non-
dispersive material (nD-1).
2.6
Wetting under load behaviour
and strength tests
These tests were carried out in a direct shear cell.
The same steps were applied as for the intact speci-
mens: a) loading at constant (initial) water content;
b) soaking at approximately 1 min (this saturation
stage was maintained for 24 hours); and c) shearing
during 1 day at constant horizontal displacement
rate of approximately 5 µm/min up to a maximum
of 8 to 9 mm. The vertical stresses applied were 52,
104, 208 and 364 kPa. During soaking at constant
vertical stress, the compacted sample underwent
some compression (collapse), which increased with
vertical stress, as shown in Figure 13. The larger
compressibility on loading and soaking (collapse)
is consistent with the larger macro-pore sizes
and macro-porosity found by mercury intrusion
porosimetry on the compacted material.
The evolution of shear stresses and vertical dis-
placements at different vertical effective stresses
during direct shear tests is presented in Figure 14.
The specimen is now essentially ductile. Dilatancy
is recorded for the low stress range (<100 kPa of
2.5
Compaction
core samples were crushed and dynamically com-
pacted in one lift using standard effort: 600 kJ/m
3
.
Maximum dry density is 1.26 Mg/m
3
(void ratio of
0.920) at water content between 32 and 37% and
degree of saturation between 84 and 97% (refer to
The pore-size distribution curve of the com-
pacted material nB-4 obtained by mercury intru-
sion porosimetry is also presented in Figure 8
together with the intact material for comparison.
The compaction process led also to a double-porosity
