Geosynthetics October/November 2022 - 29

of the main advantages in using this kind
of product is that a cuspated geonet has
comparable characteristic flows in both
machine and transverse direction.
The data available for design included
a detailed structural and hydraulic survey
of the twin tunnel containing information
about the lithology of the rock,
the presence of fractures, diaclases and
faults, with an estimation of the rock
mass rating (R.M.R.) and consequently
a definition of the required support system
(bolts with wire mesh, shotcrete and
steel sets).
Based upon the R.M.R. classification
indicated in the drawings, the geologists
have identified different categories. For
every sector, the length, the Bieniawski
category proposed, and a short description
of the rock type, has been indicated.
This information is used to quantify the
normal thrust on the tunnel vault. The
vaults to be waterproofed are 36 feet
(11 m) wide and 26 feet (8 m) high. An
extensive monitoring program has been
done on both the right and left tunnels.
A precise measurement of the water coming
into the tunnel has been conducted,
indicating for every section whether the
water is coming from the top, the left
part, the right side or from the whole
vault. Different situations have been
found from humidity to drops of water.
In certain areas the water can be measured
as 12 to 15 m³/h. (Figure 4).
It is important to notice how the situation
derived from the survey could
change in the future, after the construction
of the concrete vault, and areas
where only a few drops of water were
found could be affected by higher flows,
due to the change created by the construction
of the concrete vault. The values
obtained by the study are nevertheless
important design input that should be
used for the whole tunnels. Three critical
sections have been found (top, left/right,
all surface).
The measurements obtained are
divided by the section length to have a
required flow per running meter of tunnel
(Table 1).
The draining layer should be able to
guarantee for every section the drainage
of the water that is crossing the section
considered. As shown in Table 1, the
critical sections were the LEFT/RIGHT.
The behavior of a draining geonet
is strongly influenced by the normal
pressure applied over it. The earth pressure
over a tunnel and the load conditions
depend on several different factors
(morphology, lithology, stratigraphy,
mechanical and geotechnical properties
of the soils or rocks involved in the
FIGURE 4 Important leakages from the vault
Tunnel
TOP
ALL
LEFT/RIGHT
Left
Left
Left
TABLE 1 Design conditions
GeosyntheticsMagazine.com
29
Chain
8072-8077
6604-6607
7159-7160
Measured flow Section length
m3/h
m
12
7
15
3
5
1
qmax
m3/h/m
3
1.05
11.25
qmax
m3/sec/m
8.33 E-04
2.92E-04
3.13E-03

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Geosynthetics October/November 2022

Table of Contents for the Digital Edition of Geosynthetics October/November 2022

Geosynthetics October/November 2022 - Cover1
Geosynthetics October/November 2022 - Cover2
Geosynthetics October/November 2022 - 1
Geosynthetics October/November 2022 - 2
Geosynthetics October/November 2022 - 3
Geosynthetics October/November 2022 - 4
Geosynthetics October/November 2022 - 5
Geosynthetics October/November 2022 - 6
Geosynthetics October/November 2022 - 7
Geosynthetics October/November 2022 - 8
Geosynthetics October/November 2022 - 9
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Geosynthetics October/November 2022 - 11
Geosynthetics October/November 2022 - 12
Geosynthetics October/November 2022 - 13
Geosynthetics October/November 2022 - 14
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Geosynthetics October/November 2022 - 18
Geosynthetics October/November 2022 - 19
Geosynthetics October/November 2022 - 20
Geosynthetics October/November 2022 - 21
Geosynthetics October/November 2022 - 22
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Geosynthetics October/November 2022 - 28
Geosynthetics October/November 2022 - 29
Geosynthetics October/November 2022 - 30
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Geosynthetics October/November 2022 - cover3
Geosynthetics October/November 2022 - cover4
Geosynthetics October/November 2022 - GeoConf Brochure 1
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Geosynthetics October/November 2022 - GeoConf Brochure 3
Geosynthetics October/November 2022 - GeoConf Brochure 4
Geosynthetics October/November 2022 - GeoConf Brochure 5
Geosynthetics October/November 2022 - GeoConf Brochure 6
Geosynthetics October/November 2022 - GeoConf Brochure 7
Geosynthetics October/November 2022 - GeoConf Brochure 8
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