CIVIL FITTING OUT AND LOGISTICAL PROCESS - The Westerschelde Tunnel: Approaching Limits - page 222

A job that required special attention was the asphalting of the road surface.
This work, the asphalt was applied in three layers, was carried out as late as
possible to minimize any obstruction to other activities.
The lower layer consisted of crushed rock asphalt concrete with a thickness of
75 mm. Synthetic mesh reinforcement intended to prevent crack formation in
the asphalt was placed on top of this at the location of the cable gallery and
the electrical equipment cellars. The second layer consisted of open asphalt
concrete with a thickness of 55 mm in which detection loops were laid. The
third layer - the top layer of dense asphalt concrete - was 40 mm thick.
Study on the effects of asphalting in the tunnel on working conditions
As it was unknown beforehand what the effects would be on the working
conditions of the asphalting work in a very long tunnel, a very extensive
study was carried out on this. The study particularly focussed on the
increase in temperature in the tunnel and on the release of noxious fumes.
The study, based on a mathematical model, showed that increases in tem-
perature could be controlled well, provided that the work was carried out in
the opposite direction of the ventilation. The air temperature in the tunnel
would be roughly 22 °C at a height of 2 metres above the road surface. In
practice, the situation was even more favourable.
Fig. 14.16
Asphalting activities in
the tunnel
The release of possibly poisonous asphalt fumes, such as PAHs, also stayed
within the permitted limits, especially due to the fact that the temperature of
the asphalt fell very quickly. PAHs are only released at temperatures above
10 0 °C and the emission of these substances goes down by half with each fall
in temperature of 10 °C.The Health and Safety Inspectorate did point out that
due to the lack of experience with asphalting such long tunnels in the
Netherlands, the need to measure PAHs remained valid.
Acceleration measures have an effect
Carrying through the acceleration measures meant that the tunnel could be
opened to traffic on 14th March 2003.The backlog of 8 months had therefore
been caught up entirely.