Environmental Engineering Reference
In-Depth Information
Figure 2. location of the cracks in the PVc layer and
the extension of the zones with same settlements (s): in
yellow s < 1 m, in orange 1 < s < 2 m and in pink s > 2 m.
Figure 3.
one of the cracks of PVc impermeable layer.
b. almost 75% of the bottom surface suffered
settlements.
c. The maximum settlement was about 2,35 m,
situated 40 m distant from the bottom drainage
that was the lowest point of the bottom at the
end of the construction.
d. The drainage system suffered 65 cm settlements
and it was broken due to such movements.
e. in the bottom area far away from the drainage
point, settlement gradient is very light as there
is 230 m distance between zero and maximum
settlement points.
During the inspection, it was checked that the
waterproof layer cracks were due to great tilting
movements in a concrete piece of the drainage
system. Those movements were too localized to
be absorbed by the PVc layer without tearing.
Figure 3 shows a PVc layer crack.
To discover the origin of the problems, a geo-
technical investigation campaign was carried out
which consisted in 13 continuous dynamic pene-
tration tests (DPsh) and five boreholes. The bore-
hole length ranged between 40 and 65 m. in one of
the boreholes, five pressuremeter tests were per-
formed. With the samples taken in the boreholes,
a laboratory test campaign was made.
With all the information obtained in the
investigation campaign, some geological-geotechnical
profiles were drawn, as the one shown in Figure 4.
The bottom of the volcanic cone was occupied
by silty and clayey materials with reddish brown
colour which are saturated, very soft and plastic.
They can be described as residual soils produced
by the alteration of piroclastes and basaltic flows;
in some zones, some sand or even gravel size grains
were detected, as traces of original piroclastes y
Figure 4. Geological-geotechnical ground profile along
the longest axis of the bottom (in blue, basaltic materi-
als; in red, pyroclastic zones and in orange, halloysite clay
material).
basalts. Piroclaste zones with different alteration
degrees appeared occasionally, where the original
rock structure could be seen. The total depth of
those clayey materials was unknown, although it is
greater to 65 m, depth got by one of the boreholes
(s-c).
in the borders of the caldera, pyroclastic zones
with little alteration were detected. Those piro-
clastes are resistant materials and they have basalt
blocks inside their structure.
it is important to remark that the material
characteristics deduced with the borehole inspec-
tion were in accordance with the magnitude of the
settlements recorded. For instance, the material
recovered in borehole s-c, situated in the zone
with the greatest settlements, were the softest ones
and the ones with more water content.
