New development of a crack-limited invert slab / Neuentwicklung einer rissebeschränkten Sohlplatte

In the course of the design work of an Austrian railway tunnel, an extensive efficiency raising campaign was carried out by ÖBBInfrastruktur AG, the construction arm of Austrian Railways, which resulted in innovations to the conventional system of constructing the invert slab of waterproof concrete to seal against service water. According to the requirements for rail tunnels, a waterproof invert slab has to be constructed to prevent water from getting into the drainage pipe and thus prevent contact with formation water. In the conventional construction, this necessitates an umbrella waterproofing in the vault and a reinforced invert slab according to the ÖVBB guidelines.
The slab is subject to constraints arising from the discharge of the heat of hydration, from temperature differences and from shrinkage processes. Therefore, a high ratio of reinforcement is normally required. This led to the consideration whether for economic reasons and under the special conditions of this project it would be possible to reduce or even leave out the high percentage of reinforcement steel completely. For this reason, a comprehensive testing program with laboratory tests, a full-scale test as well as analytical and numerical investigations carried out to verify the practical applicability of this innovative system.