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Culvert Rehabilitation under the Danube

SCHIEDER-SCHWALENBERG/GERMANY, October 24, 2013 - From mid-February to mid-March 2013, Sekisui SPR Europe rehabilitated two parallel-running culverts underneath a branch of the Danube in a water protection zone of Bratislava, Slovakia. The type of water pipe and in particular the special location made it necessary using a trenchless rehabilitation technology.

Several factors posed a challenge, even for trenchless rehabilitation: a fluctuating water table of 0 - 800 cm, the high line pressure of 8 - 10 bar, and the additional challenge of two 30° and 45° bends in the 90-metre-long drinking water pipes, each pipe with a diameter of 800 mm. The Bratislava waterworks chose the r.tec® W4 Cured-In-Place-Pipe (CIPP) liner; a fully structural system. The liner was installed over the existing valve chambers to rehabilitate the corroded steel pipes.

r.tec W4

The r.tec W4 is especially designed for the rehabilitation of drinking water pipes with a diameter of 150 mm to 1200 mm. Standard manholes are often sufficient as access for the installation. | photo: Sekisui SPR

Cost and time are often decisive factors in the selection of a rehabilitation method. In the case of the culvert rehabilitation in Bratislava, Slovakia, the location of the water pipes as well as the four bends in the pipe made trenchless technology the obvious choice. The two parallel culverts to be renewed were spaced 3 meters apart, and pass underneath the branch of the Danube between Sihot, an island on the Danube, and the main street Devinska cesta in the west of Bratislava. This island on the Danube is a source water protection zone for Bratislava. The two 90-metre-long culverts, each with a diameter of 800 mm, feed the water from this source into the distribution network.

The technological solution for the rehabilitation of the corroded steel pipes was provided by the r.tec® W4 Cured-In-Place-Pipe (CIPP) liner from Sekisui SPR Europe. The glass-fibre reinforced liner has not already proven itself as safe and reliable in drinking water networks around the world; due to its material composition, it also features self-supporting characteristics: The liner can withstand high internal pressures and general external loads.

The installation of the r.tec W4

Valve chambers on each of the riverbanks provided access to the two parallel-running culverts. A gate valve on each line cut off the water supply and made it possible to completely drain and clean the steel pipes. Afterwards, the r.tec W4 liner was drawn into each of the 90-metre-long culverts by means of a pressure drum. Thanks to the liner's material properties, it was no problem at all to accommodate the four bends: two 45° bends at the start of the culverts and two 30° bends at the culvert base. The r.tec W4, which has been certified for drinking water by DVGW and KTW, is a glass-fibre reinforced polyester needle felt liner that can withstand the prevailing internal pressures of 8 - 10 bar in the culvert as well as the high external loads that result as the water table fluctuates from 0 - 800 cm. The liner owes its static characteristics to the built-in glass-fibre layer. As a result, the liner is classified as self-supporting according to AWWA Standard IV. The liner is able to support the entire load of the water pressure outside and inside the pipe, independent of the host pipe.

During the installation, the r.tec W4 is impregnated with a special epoxy resin and then cured with steam to form a new, stable pipe within the host pipe. The inner side of the new pipe consists of a watertight, hygienic coating that forms a smooth surface. As a result, water is transported at a higher flow rate, improving the efficiency of the culvert's compensation function. After the installation, which took one month from mid-February to mid-March, the rehabilitation was concluded by connecting both water lines with flange connections. After a pressure test, the gate valves were reopened and the culverts were put into operation for the next decades.