Civil Engineering Reference
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advantage that the connection between the tensile piles and the structural
floor is optimum. However, the disadvantage is that the underwater concrete
obstructs the hydration shrinkage in the structural floor. In order to deter-
mine the effects and the possible measures required, a temperature calcu-
lation was carried out. This showed that the underwater concrete on the
underside of the floor behaves like external reinforcements as it were,
whereby many small cracks come about. Additional measures were therefore
not necessary. At the top of the structural floor in the transverse direction,
the crack-width criterion of
0.15 mm was achieved with the normal rein-
forcement; in the longitudinal direction this criterion was exceeded in some
places whereby additional reinforcement was necessary.
Receiving facilities
The caisson on the northern bank served as a receiving shaft for both tunnel
boring machines. In order to make the receiving possible, a number of facil-
ities had to be applied during and after the completion of the concrete work
1st phase:
- blind ring and casing rings in the northern end wall and an impermeable
block for boring through this wall.The impermeable block, having a length
of 6 metres, was carried out as a monolithic block of low-strength mortar
(B5) within a temporary sheet pile pit which connects onto the caisson.
Firstly a layer of underwater concrete with a thickness of 1.50 metres was
cast as a bottom sealing. After the application of the impermeable block,
the temporary support of the filling of the casing rings (necessary for the
immersion of the caisson) could be removed;
- as a result of experiences with boring projects in Germany, it was decided to
fill the caisson as such, that boring on the inside could occur immediately.
The filling consisted of a shield cradle (a filling of low-strength mortar (B2)
with a thickness of approximately 4 metres), with a stepped filling of the
same low-strength mortar on top, of which the dimensions were as such,
that the tunnel boring machines could bore into this block completely with a
minor supportive pressure. Further, the caisson was filled again with water.
Fig. 8.13
Arrival of TBM in the
receiving shaft
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