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2012 Karlsruhe - Basel, Katzenbergtunnel

In the Katzenbergtunnel a high quality product of Calenberg Ingenieure was installed as a mass spring system

The Katzenberg Tunnel is the largest single component of the project to upgrade the existing and construct new sections of the Karlsruhe – Basel railway line. In order to protect the residents of Bad Bellingen from noise and vibration, a mass-spring system (MSS) was installed in the slab track in the area under the village. In a situation like this, the system must be capable of performing to the highest level.

Calenberg Ingenieure designs, manufactures and markets elastomeric sliding bearings, and statically or dynamically loaded structural bearings (elastomeric bearings) for buildings and structures, sub-ballast mats and trackbed mats for track construction as well as other elastomer-based products for noise insulation and environmental protection.

According to projections in the German Federal Transport Network Plan, the tunnel will be carrying 60 long-distance, more than 100 regional and 300 freight trains per day by 2025. This is the equivalent of a train every three minutes. In excess of 70 million tonnes of freight per year will be transported along this section, causing structure-borne sound and vibrations in the houses above the tunnel.

The main, middle section of MSS consists of the slab track, in this case the Bögl system, laid on top of a concrete slab roadbed some 34 cm thick. The concrete slab rests on USM 1000 W strip bearings The gaps between the backs of the elastic elements are covered with fibre-cement boards. This produces an MSS with a resonance frequency of 12.50 Hz, which achieves the high protective effect required of the system.

The problems in this difficult zone of conflicting demands, which otherwise would be only inadequately considered, have been neatly resolved by the expert choice of materials to provide vibration protection and drainage. Water penetrating the MSS is conducted away via the side mats on to the base slab. Longitudinal and transverse falls guide the water between the truncated cone-shaped studs into a central channel.

Calenberg Ingenieure designs, manufactures and markets elastomeric sliding bearings, and statically or dynamically loaded structural bearings (elastomeric bearings) for buildings and structures, sub-ballast mats and trackbed mats for track construction as well as other elastomer-based products for noise insulation and environmental protection.

The channel is drained by regularly spaced chambers into a main drainage pipe laid on the tunnel bottom. Access chambers are provided for inspection and maintenance of the drainage system. The USM 1000 W was specifically selected for this project. This compound product is made up of several components and was purpose-designed by our development engineers.

The truncated cone-shaped studs are made from natural rubber (NR), which has an optimum ratio of static and dynamic stiffnesses. The cones deform under increasing load into the shape of hemispheres, which results in a non-linear relationship between load and stiffness. The advantage of this is clear: the USM exhibits an almost constant natural frequency over the range of compressive stresses commonly encountered in track engineering.

Only in this way can the system provide constant protection against structure-borne sound and vibrations across a range of different loads. The back consists of two layers, each of which has a different function. The rubber mixture of the middle layer functions as a damper that attenuates any increase in the natural frequency and makes the amplitude of the vibrations decay more quickly.

Chloroprene rubber (CR) is used in the covering and wear layer, making the system extremely robust against the effects of mechanical loads. Two vulcanised fabric layers give the back of the USM stability and prevent undesirable transverse strains.

Our USM strip bearings can be laid longitudinally. The manufactured width of the material is approximately 1.54 m, which is cut into 64 cm wide strips. To make handling the material in the tunnel easier, it was agreed with the contractor to supply the product in 50-metre rolls. USM 2020 and USM 3000 were used over the whole surface in the transition zones.

After the USM 1000 W was put in place, it was covered with fibre-cement boards and the longitudinal and transverse joints sealed. This provides the certainty that no fresh concrete can enter the area below the elastic elements.

The concrete slab reinforcement is placed on the robust backs of the sub-ballast mats. An additional protective layer is not required for the elastic elements. After the concrete has hardened, the slab is ready to accept the Bögl slab track components. These were unloaded from lorries and placed using a crane before being grouted in position to connect them monolithically with the slab.

As the slab track is traffickable by road vehicles, the tunnel tubes also serve as access for the rescue services. Correct bearing support of the chamber covers was particularly important to transfer the wheel loads. This was achieved with a total of more than 2.5 km bi-Trapez bearings.

Extensive tests were carried out for this project to determine the static and dynamic stiffnesses and long-term behaviour. These tests were carried out in accordance with the new standard DIN 45673 – Part 7.

In the design phase, approval tests were specified to demonstrate the suitability of the material and provide the principles for the design calculations. Special requirements for in-house supervision during production ensured that the values quoted in the approval documentation were also reproduced in the manufactured material sent to site for use in the works.

Random samples were taken during installation. The attainment of the required values was checked by independent third-party inspection. In our case, the inspection was carried out by the German Federal Institute for Materials Research and Testing (BAM), Berlin.

All this effort is necessary to ensure the long-term proper functioning of the elastic elements in an MSS. Together with the information about the other components of the MSS, the documents were submitted for BD Netz AG approval. After examination, an in-house approval was granted for the MSS.

After completion of these technologically advanced works, the railway agency departments involved and the contractor were so impressed that a full-scale model of the MSS was set up in the DB visitor centre and in the grounds of contractor's main offices. Visitors to both these premises can easily see the advantages of this form of construction.

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