Geosynthetics October/November 2022 - 28

Drainage geocomposites and PVC geomembranes for highway tunnel lining
protected from puncture, as the gunite is a
rough surface (Figure 1 on page 26).
The waterproofing layer prevents
contact between the water and the concrete
vault. The water coming from the
gunite should be drained away, not to
cause a concentrated excessive water
pressure on the structure that could cause
an excavation in the gunite layer. For this
reason, it is recommended to install a
protection-draining layer between the
gunite and the geomembrane.
The main requirements for this prodFIGURE
2 Effects of water infiltrations into a tunnel
FIGURE 3 Cupsated geonet
formulated, designed, certified and CE
marked according to the main European
standards for specification. During the
design phase, it is important to consider
mechanical, physical and chemical factors
that can affect the life of the geomembrane
in relation to the life required
for the project in question. The European
harmonized standard for geomembranes
used for applications in tunnels is the
EN 13491 " Geosynthetic barriers -
Characteristics required for use as fluid
barrier in the construction of tunnels and
underground structures. "
In general, PVC-P geomembranes
used in civil engineering application
have a thickness of 2.0 mm or higher,
depending on the specific conditions of
the project.
Design and selection
of geosynthetics
The typical excavation sequence in rock
calls for use of a gunite layer over the rock
itself to reduce the roughness of the profile
and smooth its surface. Considering the
very high loads that could be applied to the
concrete vault, the geomembrane must be
28
Geosynthetics | October November 2022
uct can be summarized as follows:
* High compressive strength (> 500 kPa)
* High discharge capacity
* Resistance to puncture
* Flexibility and easiness of installation
The market of geosynthetics can propose
a wide range of product; not all of
them fully cover all the requirements
listed above.
The original proposal consisted of a
nonwoven geotextile (500 g/m²), which
is very flexible and effective against
puncture but inadequate for drainage of
high flows and unable to resist against
compressive stresses. Furthermore, this
kind of product may experience severe
clogging, as the solid part is contained
in the water.
A good alternative is to use drainage
geocomposites with a cuspated geonet
(Figure 3) as a core. These products meet
all the requirements previously listed, are
flexible, and are able to guarantee a very
high draining capacity even under very
important compressive stresses because
of their very high compressive resistance
and excellent puncture resistance.
Cupsated geonet has a flat edge and
a cuspated edge. The cuspated edge is in
contact with the gunite layer. A nonwoven
geotextile, 500 g/m², was bonded to the
flat edge to be in direct contact with the
PVC-P geomembrane to help the geonet
in its puncture-protection function. One
Geosynthetics October/November 2022

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