Volume 7, no. 13 - Colbond Geosynthetics

Waterproofing system
The waterproofing system, consisting
of the drainage and protection layer
and the waterproof liner, plays an
important role in the NATM tunnel
design.
The drainage and protection layer
functions as:
• drainage on the outside of the
tunnel
• cushioning layer between rock face
and concrete structure
• protection of the waterproof liner
The waterproof liner offers protection
against leakage.
The waterproofing system must be
continuous and easy to handle and
install.
As during installation and use, the
waterproofing system is exposed to
extreme mechanical, physical,
chemical, and - incidentally -
biological loads, the materials must
be resistant to these loads. They
must also be able to adapt to
irregularities of surfaces on which
they are installed and may not cause
any harm to the environment.
Challenging aspects
The prestigious NEAT project
includes a variety of striking and
challenging aspects.
The long base tunnels will provide a
modern flat-trajectory line, allowing
for substantially longer and heavier
good and passenger trains that travel
twice as fast. The latter trains can
even reach a speed of some 200
km/h.
Such trains cannot be used on the
existing Alpine lines, due to the steep
grades and small radii of curvature.
The flat-trajectory involves unusually
deep construction - maximum
overburden is 2,300 m - and high
temperatures, which can reach 45ºC.
The water pressure from strata
overlying the Gotthard base tunnel
has been estimated at as high as 100
bar.
High demands
In view of the exceptional conditions,
the materials to be used for the
construction of the two base tunnels
must meet the most stringent
requirements for a designed service
life of 100 years.
Waterproofing systems, however, are
relatively “young” and have only
available for 30 years. This means
that no long-term experience has
been gained with these systems.
Consequently, for this part of the
tunnel construction the requirements
Colbond Geosynthetics News 13 - 2002
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