Cable Protection Pipes as ready-made empty Duct Pack
Together with the Heibel GmbH trade agency the JV Katzenbergtunnel developed a novel system for laying cable protection pipes as ready-made parts in “pack form”. This saves time and space, the quality is enhanced.
At peak period almost 450 persons are involved in building the Katzenberg Tunnel – on a roughly 100,000 m² large construction site. For projects of this size the planning has to be meticulous calling for individualised solutions. The JV Katzen-bergtunnel devoted special attention to laying cable protection pipes for example. These protect power and telecommunications cables laid at the verges during the scheduled 70-year service life of the tunnel. Some 360,000 m of cable protection pipes wind their way through the 2 tunnel bores. Consequent-ly the cable protection pipes and their installation represent a considerable cost factor.
Thus the JV Katzenbergtunnel in conjunction with Heibel, who supplies the cable protection and extinguishing water pipes for building the Katzenberg Tunnel, came up with a novel system for laying the pipes: ready-made “empty duct packs” – thus applying a new method in tunnelling. In the case of the Katzenberg Tunnel the planning team broke new ground by laying the cable protection pipes in “empty duct packs”. Cable blocks with 16 cable protection pipes were concreted in advance in the JV Katzenberg-tunnel’s production plant. Pre-fabrication possesses the advantage that the ready-made parts only need to be set together in the tunnel bores – by means of fixed pipe connections.
Space-saving Installation of the Pipes
As the Katzenberg Tunnel consists of 2 parallel running bores and the individual tunnels are considerably smaller than in the case of a single-bore tunnel, the project team was first and foremost faced with a space problem. Dipl.-Ing. Josef Sautter, the JV Katzenbergtun-nel coordinator explained the difficulty: “Owing to the use of single-bore tunnels there was very little room to build the verges for installing the cable protection pipes. Only by dint of consistent prefabrication of individual structural parts was it possible to construct 2 x 60 m reinforced verges in each bore per day”.
Furthermore it was feared that if the 16 cable protection pipes were to be installed separately in the tunnel this could lead to difficulties on account of the lack of space between the individual pipes. The reason: the risk that empty spaces are created when concreting the cavities between the cable protection pipes is prevalent during the “conventional” construction method. Such “air holes” would exert a negative effect on the quality of the structure. The selected solution on the other hand ensures that the gaps between the individual empty ducts for the cable can be filled with concrete without cavities being created.
When the prefabricated parts are manufactured it is guaranteed that the cable protection pipes attain the necessary stability thanks to steel pipes set in their interior thus ensuring that they are not damaged by concrete and retain their original form. As a result the pipes are not deformed in spite of uplift when the empty duct packs are concreted. The steel pipes can also be removed without any problem when stripping the concrete. Through various test runs with the help of which the stability of the novel laying process for the corrugated cable protection pipe S 110/94 PE.HD was confirmed, the DB AG as client was also convinced about deployment of the corrugated pipes. They possess a lower material weight per metre and lead to not inconsiderable savings in terms of material costs compared to complete pipes for cable protection.
The lower material costs amounting to some 50 % as opposed to conventional complete pipes for cable protection thus offset the more expensive prefabrication of the empty duct packs. Furthermore the laying method leads to improvements in meeting deadlines and quality of performance given constricted space conditions. Thus it is suited e.g. for building verges in the single-bore mainline tunnels planned in future by the DB for safety reasons.
Through prefabrication at the contractor’s own concrete precast plant the 16 roughly 6 m long individual pipes can be precisely laid parallel to one another practically to the millimetre. Thanks to the exact positioning of the pipes with one another individual cable pipe blocks can then be joined together in the tunnel unproblematically. At the same time working space and construction time can be saved during the subsequent building of the verges in the tunnel thanks to outside prefabrication. In this way the installation rate for producing reinforced verges in the tunnel is enhanced and in turn completion of the internal furnishing of the tunnel pipes speeded up.