Prague: Integrity Testing After Vltava River Crossing

Connection of a Wastewater Treatment Plant

The connection of the Podbabsk wastewater treatment plant in Prague to the central treatment plant on the Vltava River island Císařský presented major challenges for the general contractor ZEPRIS. To increase transport capacity, a double pipeline with dimensions of 400 x 23.7 mm was installed, along with five manhole structures on the island. The total length of the pipe string is approximately 1,050 m. The trenchless sections crossed beneath the Vltava as well as old tree growth along the river bank.

The trenchless installation using the HDD method beneath the Vltava riverbed was carried out by TALPA-RPF. The start and end points of the river crossing were already predetermined by the connection points of the original pipeline. Due to these fixed points, a relatively short distance, and the resulting tight bending radius, the drilling was demanding. The pilot drilling was also a major challenge, particularly on the bank side. Due to the shale rock in the area of the drill channel, the geological conditions were unstable and could have caused difficulties in the area of the borehole during pipe pulling. Due to the longitudinal profile of the siphon and the very demanding geology of the subsurface, the SLM® DCT pipe was therefore selected, which enables an integrity test directly following installation.

After 18 days, the reaming of the two 160 m long pipe strings beneath the Vltava was completed. During technical monitoring of the construction, the operator was able to verify the quality of the installation and the integrity of the installed pipelines multiple times. The design office was able to successfully prepare the project documentation.

“We used the system that enables inspection of PE pipes after installation for the first time. However, the positive experience will certainly lead to further use in our trenchless construction projects,” explains Ivan Demjan, Managing Director of TALPA-RPF s.r.o.