Environmental Engineering Reference
In-Depth Information
Table 2. Pressuremeter tests carried out in the boreholes
at the upper reservoir.
with geophysical techniques (electrical tomography
and seismic refraction) the position of the bedrock
has been estimated at a depth varying between 25
and 40 m, with the deepest areas being in south-
ern part of “la caldera” at around 35-40 m. This
substratum is made up of alternate lava flow layers
and pyroclastic levels, predominantly scoria.
The process of obtaining undisturbed samples
from these materials was complicated, as drilling
caused their crumbling; these materials therefore
had to be studied with in-situ tests: pressurem-
with the conclusion that the foundation of the
basin had low load bearing capacity and high
deformability.
on the basis of the investigation, the following
stratigraphy was adopted in order to estimate the
settlements:
- From 0 to 5-6 m deep: colluvial deposits made
up of material that had fallen from the slopes
(sand and gravel size, with pebbles and even met-
ric blocks of basalt), and altered in situ (Qc).
- From 5-6 to 15 m deep: material making up the
fill of the bottom of “la caldera”, with grading
and geotechnical properties closer to the group
of lapilli (Mhs).
- From 15 to 25 m in depth: ill material with gran-
ulometry and geotechnical properties closer to
the scoria group (Mhi).
- at a depth varying between 25 and 40 m contin-
uous competent levels were detected, which have
been interpreted as basaltic flow layers. These
are considered to be non-deformable (B+e).
The deformation moduli were obtained from
the in situ tests.
Borehole
Pressuremeter tests
Depth
(m)
Depth
(m)
ep**
(MPa)
ep*
(3)
(MPa)
name
lithology*
sc-1
20.6
-
-
-
-
sc-2
36.2
4.20
Qc
4.9
-
28.70
B
679.8
-
35.90
e
29.3
-
sc-3
32.6
2.00
Qc
2.1
-
5.70
Mh
4.2
-
10.20
Mh
15.6
-
sc-5
20.6
-
-
-
-
sc-6
25.6
3.20
Qc
2.8
-
7.90
Mh
8.3
-
14.70
Mh
11
-
19.70
Mh
8.1
-
sc-7
50.0
-
-
-
-
sc-8
25.5
26.20
e
64.9
-
sc-9
45.0
9.70
ec
122.6
-
21.20
a
23.1
-
29.70
B
25
-
39.20
B
744.4
-
sc-10
32.0
-
-
-
-
sc-12
20.6
-
-
-
-
sc-13
25.0
-
-
-
-
s-1
30.0
10.55
Mh
15.7
31.1
15.00
Mh
14.4
14.4
22.00
Mh
2.3
2.9
30.00
Mh
27.2
34.4
s-2
30.0
9.50
Qc
10.5
10.5
s-3
30.0
10.50
Mh
14.7
31.5
15.00
Mh
3.6
6.1
22.50
Mh
14.7
17.0
30.00
Mh
36.7
70.7
s-4
30.0
11.00
Mh
15.3
16.7
16.50
Mh
19.0
28.5
22.50
Mh
16.7
17.4
30.00
Mh
72.9
92.6
s-5
30.0
8.50
Qc
5.9
33.3
4.1
Estimation of settlement caused
by the filling of the basin
The settlement due to the filling of the basin was
calculated using the elastic method, taking into
account the sole treatment of the removal of the
loosest colluvial material, which would be sub-
sequently re-placed and compacted, which was
assigned a resulting modulus of 20 MPa.
The settlement associated with the filling in
of the reservoir, using elastic moduli deduced
from the compacity of the material and derived
from the pressuremeter tests was 35 and 25 cm,
respectively.
although this settlement could possibly take
place without causing the failure of the basin
impermeable membrane, it is worth limiting the
differential settlement. in order to do this it was
considered necessary to treat the ground to limit
the total settlement to 10-12 cm.
15.50
Mh
15.3
15.3
20.50
Mh
3.9
18.6
30.00
Mh
35.8
42.7
* Qc, colluvial deposit; Mh, bottom fill material at “la
caldera”; B, basaltic lava layers; e, scoria; ec, consoli-
dated scoria; a, almagra.
** ep, pressuremeter modulus obtained from first load.
*
(3)
ep, pressuremeter modulus obtained from reload.
4
GeneRal DescRiPTion oF The
PRoBleM anD solUTion aDoPTeD
The location of the upper reservoir is in a spot
known as “la caldera”. The materials supporting
the basin are made up of fill material and colluvials.
on the basis of the models that have been obtained
