Volume 7, no. 13 - Colbond Geosynthetics

Enkamat ® & Enkadrain ® :
High-performance flexibility
18 Colbond Geosynthetics News 13 - 2002
In tunnel-building, Enkamat and Enkadrain serve a
number of specific functions. In addition to
protecting the waterproof liner and allowing an outlet
for runoff and seepage, as seen at the Giswil tunnel
and others using the NATM technique, these
products are also used in open-cut tunnels to
provide drainage on the outside. In special cases,
they can even serve as a grip-layer for the shotcrete
lining.
The insensitivity to clogging of these geosynthetics, their
easy installation, proven high performance and low
inflammability make Enkamat and Enkadrain the drainage
materials of choice for mined and bored tunnels, open-cut
techniques, tunnel repair and special projects (such as the
use of injection and expansion layers and the fabrication of
micro-tunnels for power stations).
In tunnels that are blasted or bored using a Tunnel Boring
Machine (TBM), the installation of geosynthetic drainage
mats and waterproof lining commonly begins after a period
(6 months to a year) of monitoring rock settlement.
The shotcrete sprayed first is very rough material indeed,
with surface irregularities of up to 10 mm. After the
shotcrete has dried, seepage and leaks may become
visible. These spots require drainage, but can in the course
of time wander and reappear at other places in the tunnel
wall. Local drainage is therefore not enough: lining the
entire tunnel wall with drainage material is the choice of
most specifiers.
Enkamat is attached to the shotcrete wall with shoot nails,
fitted with PVC disks. And because of its flexibility and
structure, Enkamat adheres well to even the most irregular
shotcrete wall.
The waterproof liner is attached starting at the roof of the
tunnel, and working down. For this purpose, a special
hydraulic rolling scaffolding is used. Once the sheets of liner
are in place, they can be double-welded along the seams,
and to the drainage system at the bottom of the tunnel wall,
and tested for impermeability by means of compressed air.