Dewatering, waterproofing and drainage - Tunnel Engineering: Basics and Additional Services for Design and Construction - page 233

5.3.4 Testing of seams in waterproofing membranes
Continuous testing during installation is important since later patching and repair is practi-
cally impossible. The following testing methods are used in practice or are regulated in
Germany by DIN standards and further guidelines:
1. Testing by visual inspection; additional determination of the seam geometry accor-
ding to [DVS guideline 2225-5] for waterproofing membranes.
2. Tapping to sound multi-layer waterproofing for voids. This demands particular expe-
rience.
3. Testing the behaviour of a welded membrane seam in a shear test according to DIN
EN 12317-2.
4. Scratching the seam with a nail or scoring tool.
5. Testing the behaviour of a seam in a peeling test according to DIN EN 12316-2.
6. Blowing the seam from the side with compressed air.
7. Spot checks at some points.
8. Electrical testing with high-voltage. The testing area is probed with an electrode and a
spark occurs at defective locations. The precondition is that the support is conductive
and the waterproofing layer to be tested has a lower electrical conductivity than the
support.
9. Compressed air or compressed water testing of joints: the joint is made as a hose and
filled with compressed air or water. Loss of pressure indicates a leak. References like
[EAG-EDT] state the necessary testing pressures, durations and permissible pressure
loss.
10. Electrical testing of joints: a metal strip is laid in the joint and tested with a high-
voltage device.
11. Vacuum testing of joints: similar to pressure testing, but the air is sucked from the
outside.

5.4 Tunnel drainage

The use of drainage to reduce groundwater pressure in road and rail tunnels is a function-
ally reliable and in many cases also economic construction principle in order to be able
to construct tunnels under high water pressures. Drainage measures have to be provided
for the temporary construction state and the completed state. Drainage measures in the
temporary construction state have already been dealt with under 5.2.2.1.

The disadvantages of tunnel drainage that have become increasingly apparent in tunnel-
ling work in recent years are the permanent intrusion into the natural groundwater system,
which has already been discussed in the introduction, and the sometimes very expensive
maintenance of drainage systems due to sintering (Fig. 5-31 and Fig. 5-32).
Depending on the design, construction and geological conditions, the cost of maintenance due
to sintering for cleaning tunnel drainage can be considerable, and can in some circumstances
exceed the extra cost of the alternative of a completely waterproofed tunnel. Investigations at
the Institute for Tunnelling and Construction Management at the Ruhr University, Bochum
have however shown that the basic principle of a drained tunnel still remains an optimal con-
cept even considering the high maintenance cost in many areas due to sintering [209].