THE MAGAZINE FOR THE DRAINAGE, WATER & WASTEWATER INDUSTRIES
CASE STUDIES
ultimately the orography of the Temo river valley, through which the rehabilitation section runs. The area between the start and the end point is protected by numerous environmental regulations and has no public access roads.
Under these conditions, an open rehabilitation of the pipeline was impossible and ruled out from the start. But planning an intervention with trenchless technologies was also extremely difficult and quite daring.
The implementation
The trenchless technology selected by the network operator is the Primus Line® system. Its basis is a flexible, multi-layer aramid- reinforced high-pressure liner and specially developed connectors.
Access to the pipeline was provided via several shafts with valves and fittings along the route, so that even selective excavations for foundation pits could be completely avoided. The intrusion and impact on the pipeline and the surrounding area could thus be reduced to a minimum.
The precise organisation of the intervention phases ensured optimum execution of the work and minimised pipeline downtime. The project was divided into only three construction phases, mainly enabled by the special and efficient bypass
FOLLOW US
solution, also realised with Primus Line® technology.
After the separation of the old pipe in the shafts and the video inspection the liner was pulled into the pipe by means of a winch. In some cases, installation lengths of up to 1,000 metres were realised in one piece. For this purpose, the technicians from Benassi and the material manufacturer Primus Line carried out a feasibility test in advance for each pull-in section, taking into account the frictional forces that would arise. In doing so, an attempt was made to precisely determine the optimum ratio between the greatest possible care for the material and optimum utilisation of its performance capability and high tensile strength.
In view of the asbestos cement of which the old pipe is made, the underground work was carefully planned. Compared to the classic open construction method, the risk of spreading asbestos fibres is lower with trenchless rehabilitation technologies anyway. Nevertheless, appropriately trained personnel are needed to carry it out.
After the liner is pulled in, the specially designed connectors are used to reconnect the pipeline. For this project, Primus Line provided a custom solution for anchoring to the pit wall so that each connector could be inserted into the existing structures to save space. This allowed maintenance of the existing shafts and avoided additional excavation for the new construction.
After the successful pressure test with 20 bar
at the lowest point of the pipeline and the disinfection of the pipeline with chlorine solution every two kilometres, the reconnection to the rest of the pipeline followed. Afterwards, the bypasses could be emptied, removed and used again.
Tailored project workflow
Decisive for the success of the project was not only the specialisation of all those involved, but also the close interaction between those responsible for the product and those responsible for its implementation throughout the course of the project. Last but not least, this guaranteed an economical implementation of the measure.
An initial variant study considering different trenchless solutions such as sliplining with HDPE, CIPP and Primus Line® showed significant technical and economic advantages. while at the same time reducing the installation risks. In addition, the challenging site conditions due to the difficult-to-access terrain made open trench construction much more expensive and time- consuming, which made the renovation with Primus Line® the preferred solution.
"Only the extraordinary application possibilities of the Primus Line® technology made it economically possible to carry out this otherwise extremely costly and impractical maintenance work," concludes Project Manager Matteo Lusuardi from Benassi.
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