Civil Engineering Reference
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lining being 0.45 metres. An important difference to the reference design
was the road surface which was not based on a supportive concrete sheet,
but on a backfill of sand-cement stabilisation. Besides, the length of the tun-
nel was shortened to 6,315 metres. This was possible by reducing the soil
covering to 12 metres and by stabilising the bedding of the Westerschelde
by means of placing a stable 'threshold' up to 32.50 metres -NAP on the
bedding of the Westerschelde at the position of the Pas van Terneuzen. The
design also provided for the fixation of the bedding on the northern side of
Everingen.
Fig. 2.8
Original design
by KMW
(distances/dimensions
in millimetres)
12,300
11,400
∼
13,000
12,300
450
450
450
11,400
450
Cable gallery
150
100
150
3,500
3,500
Escape
corridor
Cross connection -
500 m
Design is too expensive; alternatives are necessary
Although the offer by KMW was realistic and substantially lower than the
offer by KWOV, the price had to be reduced by at least 70 million euro
in order to make the project financially feasible as a toll charging tunnel.
Since the optimization of the design (on costs) only led to marginal cost
effects, the parties involved decided to develop an alternative and cost-
reducing design. Of the developed alternatives, the following were con-
sidered feasible: a larger tunnel with a single tube and an alternative
which involved two smaller tubes.
Tunnel with 1 tube
The outer diameter of the tunnel with 1 tube measured 13.50 metres,
whereas the lining was about 0.50 metres thick. The design provided for a
road on two levels, one for each driving direction. In order not to have to
bore too great a diameter, the structure gauge was reduced from 4.50 metres
to 4.20 metres.The width of the left-hand driving lane in the design was also
narrowed from 3.50 to 2.75 metres. Only passenger vehicles would be per-
mitted to make use of this narrower driving lane.
Twin-tubed tunnel with a smaller diameter
The second alternative consisted of a tunnel with two tubes with an outer
diameter of 11 metres and a lining with a thickness of 0.45 metres. The
choice for the smaller diameter, as a result of the expungency of the
separate longitudinal escape corridor with cable gallery, made it possible to
disregard the construction of a stable 'threshold' on the bedding of the
Westerschelde at the position of the Pas van Terneuzen. This design also
provided for the construction of cross connections every 500 metres. This
distance remained 500 metres based on the probabilistic calculations.
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