Civil Engineering Reference
In-Depth Information
Fig. 9.6
The application of the
temporary bolt
connections
The pre-tensioning of the lining in the longitudinal direction is not guar-
anteed in the starting and receiving shafts. That is why a permanent bolt
connection was chosen over a length of 30 metres (15 rings). It was calcu-
lated that after this distance the friction of the soil around the tunnel would
be high enough to keep the lining pre-tensioned and thus to compress the
rubber seals sufficiently. Due to the fact that the tunnel is required to have a
100 year life span, the permanent bolts were made of stainless steel.
Concrete and reinforcement
The forces acting on the lining, which were governed by the forces in the
construction stage, made it necessary to use reinforcement. In order to
determine the bending reinforcement in the tangential direction, the bend-
ing force and normal force were evaluated. The favourable effect of the
normal force could be taken into account. For all combinations of (possibly
occurring) loads, it appeared that the chosen minimum reinforcement
(
10-100 inside and outside) was applicable throughout.
A high normal compressive force is present on all joint surfaces (ring and
longitudinal joints).This made it necessary to apply splitting reinforcement.
This reinforcement should be applied at the longitudinal joints to withstand
the high normal compressive force of the ring and at the ring joints to with-
stand the enormous thrust force of the TBM.
Concrete covering and life span
The design of the segments assumed a concrete grade of B55. The mesh
reinforcement consists of ribbed concrete reinforcing steel. In view of the
life span requirement, on the basis of a probabilistic point of view, a 50 mm
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