Dewatering, waterproofing and drainage - Tunnel Engineering: Basics and Additional Services for Design and Construction - page 219

In order to take into account the different shrinkage behaviour of various construction ele-
ments (transition invert - wall), the nominal reinforcement in the distribution direction of
horizontal working joints is to be doubled up to 1.5 m above the joint.
The construction of a section without working joints requires an expensive formwork unit.
Concrete cover. Corrosion increases the volume of the reinforcement and can cause con-
crete spalling. Since the penetration of water can never be completely prevented, the mini-
mum concrete cover inside the tunnel should be nominally 50 mm and on the outside
60 mm.
Concrete technology
Water-cement ratio. According to DIN 1045, the water-cement ratio of elements 10 to
40 cm thick may not exceed 0.6 or for thicker elements 0.7 (Fig. 5-18) . In order to consider
the variation of site mixing, the W/C ratio should be set about 0.05 less for site batching,
although lower values are desirable. Concrete is tested according to DIN 1048 .
Figure 5-18 Waterproof concrete. Reduction of the maximum water penetration depth
with increasing hardening duration [26].
The aggregates should be as dense as possible and have a compact shape, and the grading
curve should lie within the most favourable zone.
A cement should be selected, which only develops low heat of hydration, in other words a
slow-hardening cement; this requirement is in contradiction to the required short striking
time. The fines content (passing 0.063 mm sieve) should be between 350 and 400 kg/m 3
solid concrete.