Geosynthetics October/November 2022 - 27

Drainage geocomposites
and PVC geomembranes
for highway tunnel lining
By Daniele Cazzuffi, Massimo Cunegatti and Piergiorgio Recalcati
T
he original design for the primary lining system for the Driskos Twin
Tunnel along the Egnatia motorway in Greece, consisting of a PVC plasticized
(PVC-P) geomembrane, called for a nonwoven geotextile, 500 g/m²,
as a puncture protection and drainage layer.
The nature of the rock with high pressures expected on the concrete
vault, as well as the huge amount of water that was encountered during
excavation, was making it necessary to substitute the geotextile with a highperformance
drainage geocomposite. It needed to be capable of guaranteeing
an effective drainage under high pressure for the whole design life and
to drain the water at 360° within the plane to allow efficient drainage even
during concentrated water flows. This article describes the evaluation of the
design state of stress on the geocomposite, the required drainage capacity,
and the waterproofing performances chosen as the best technical solution.
After more than 15 years, the drainage lining system is still working perfectly
and no problems have been encountered.
It is well known that excavation of tunnels crossing a phreatic surface
without a lining system reduces the water pressure to zero along its edge.
This causes a water flow from the aquifer to the tunnel. The effect of this lack
of waterproofing can be a subsidence in the area surrounding the tunnel, the
drying of wells and springs (Figure 2 on page 28).
Apart from the damages that can result in the surrounding area, the presence
of water in the tunnel can create a risk situation in the tunnel itself. This
is mainly due to the possibility of water (or ice in the winter ) on the road, ice
stalactites on the roof (obviously only in very cold regions and close to the
tunnel entrance), and corrosion of the steel of the concrete vault. These risks
can be avoided by using a properly selected geomembrane that guarantees the
waterproofing of the vault.
For this application, geomembranes made with flexible PVC (PVC-P)
are widely used, thanks to their flexibility, high mechanical resistance and
easiness of application. These types of geomembranes must be specially
PROJECT HIGHLIGHTS
EGNATIA MOTORWAY-
RISKO TUNNEL DOUBLE
TUNNEL 6KM
CONTRACTOR
Hellenic Ministry-EU
(Egnatia ODOS S.A)
CONSTRUCTION COMPANY
Aktor S.A
WATERPROOFING AND
DRAINAGE SUBCONTRACTOR
Domissima S.A
GEOMEMBRANE
Flagon BSL 2,0 MM (Flag
SPA-nowadays Soprema SRL)
GEOCOMPOSITE FOR DRAINAGE
Tenax TDP 700 and 1000-
Domodrain 1200 and 1500
(Tenax SPA)
Daniele Cazzuffi is geotechnical
engineer at CESI SpA, Milano, Italy and
past president of the International
Geosynthetics Society (IGS).
Massimo Cunegatti is technical director at
Soprema s.r.l., Chignolo d'Isola (BG), Italy.
Piergiorgio Recalcati is technical director
at Tenax SpA, Viganò (LC), Italy.
All figures courtesy of the authors.
GeosyntheticsMagazine.com
27
http://www.GeosyntheticsMagazine.com
Geosynthetics October/November 2022

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