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without there really being optimum co-ordination between design and imple-
mentation. As in the traditional situation, designing and building are separate
worlds, this separation in actual practice at the WesterscheldeTunnel was not
eliminated in many cases, in spite of the design and build contract.
General contractual clause about unforeseen risks causes interference
The boring, building and design risks were defined within the contract in
addition to a standard (umbrella) article concerning unforeseen risks, intended
for other matters. This nevertheless caused unnecessary interference. It
would perhaps have been more advisable if a number of large risks had been
elaborated in the contract based on research, and to reach agreement about
penalty arrangements (spread of risks concerning costs) and not to have
included an article about unforeseen risks.
Environment sets new safety requirements
A project can - also after a contract has been signed - be confronted with
new requirements which are set by the environment. The safety of under-
ground structures was right at the centre of interest in the Netherlands in
the mid 1990s. Next to the statistical estimate of safety risks carried out, a
scenario analysis was also required and from this the requirements were
strengthened.This specifically translated into doubling the number of cross
connections between the tunnel tubes from 13 to 26. Bearing in mind a
possible disaster, an escape route had to be created every 250 metres
instead of every 500 metres. Furthermore, the heat-resistant cladding of the
lining also had to be considerably thicker.
Fig. 17.3a
Extending the scope;
cross connection
under construction
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