Environmental Engineering Reference
In-Depth Information
Figure 6.
Geological profile.
Figure 7. cross section of primary support and execu-
tion phases.
Table 1.
Geotechnical parameters.
γ
(kn/m
3
)
φ′
(°)
c′
(kPa)
e
(GPa) ν
complex
k
0
(15 cm thick) with heB140 steel ribs spaced 1 m.
all the upper zone of the cavern, excavated in recent
deposits, was executed under the protection of a
group of three sets of φ73 mm sch40 forepoles,
spaced 30 cm, each with a total length of 12 m.
The lower part of the station was built in levels,
3 m high, allowing excavation steps of 3 m (12 m
apart between different levels in the longitudinal
direction). The primary support for this part of the
structure consisted of shotcrete with fibres (20 cm
thick) and a rockbolt mesh of 1,5 m × 2,0 m, to
prevent the rock mass from decompressing, caus-
ing, eventually, blocks from falling. For the upper
levels, self-boring, 9 m long Mai R38n rockbolts,
were adopted, while for the lower levels, 6 m long
super swellex bolts were chosen (
Fig. 7
).
For the top wall, it was used shotcrete with
fibres (20 cm thick). also rockbolts were applied
in the same pattern and type as described for the
transverse direction.
considering the hydrogeological characteristics
of the rock mass, a drainage and a waterproofing
system was designed to the external contour of the
upper section of the pumping station, comprising
a PVc geomembrane (e = 2 mm) over a geotex-
tile (500 g/m
2
) with draining functions. The col-
lected water is directed by gravity to geocomposite
drains of stabidrain type (0,30 m × 0,04 m), placed
throughout all the pumping station perimeter,
being finally delivered into the station, in the stor-
age area, by cross drains in PVc pipes with Ø90,
spaced 3 m.
alluvia
21
32
60
1
0,38
0,65
Breccia
22
36
80
1,5
0,38
0,65
2.3
Construction method and support system
Due to the geological and geotechnical characteris-
tics of the hillside where the portal of the pumping
station is located, the construction works started
with its consolidation.
in order to execute this works a provisional
rockfill with 8 m height and 1h/1V slopes, was
constructed over the existing platform, with the
rock material resulting from the excavation of the
auxiliary tunnel.
When this phase ended, the excavation of the
station was started from the top by levels. limits to
the progression of the excavation were prescribed
according to the geotechnical characteristics of the
materials found during the excavation.
Because the roof arch has a small cover and
is totally located in alluvia, the excavation of the
cross section in the upper part of the cavern had
to be done in more than one stage, as seen in
Figure 7. Firstly, a pilot tunnel was built with exca-
vation steps of 1 m, which allowed to verify and
validate the assumed geological and geotechnical
conditions. Then, the complete top heading and
the first bench were excavated, leaving a 12 m dis-
tance between each section.
The primary support used in the top heading
consisted in 20 cm thick of shotcrete with fibre
reinforcement and steel ribs (heB200) spaced 1 m,
supported at the base by 9 m long rockbolts (self-
boring Mai R38n). For the pilot tunnel, it was
used a support consisting of shotcrete with fibres
2.4
Final lining
The choice of the concrete class to use on the
final lining and on the pumping station inter-
nal structures (c30/37) was determined by the
