Installation in an underground tunnel

ECOPAL 2.0 ND/ID 500 flanged corrugated pipes

The purpose of the work was to proceed with the reconstruction of a section of the sewer located inside an underground tunnel under Piazza Emanuele Filiberto in Pavia’s historic centre. About 200 meters of an old fiberglass pipeline collapsed inside an iron pipe bear by iron braces. The collapse was caused by black water from the houses in the square and rain waters from the grids placed in the streets: the excessive weight of the double pipeline (steel + fiberglass) in addition to the weight connected to the conveyed flows and the age of the system led to leakage of sewage into the ground.

There were different conditions to comply during reconstruction:

• the planned pipeline had to have a low weight since the channel had to be positioned above braces and handled and installed manually or with small footprint machinery due to the narrow spaces inside the tunnel. The particular location of the tunnel (within a green area away from public roads) also required the possibility that the pipeline sections could be moved by hand for transport from the yard depot to the installation point;
• the pipeline had to have a wide range of special pieces and the possibility of creating custom fittings such as specific angle bends due to the particular conformation of the host tunnel (not straight and with significant angular deviations);
• the pipeline had to allow the realization of watertight connections in variable and undefined positions;
• the channel had to include different pipe-to-pipe connection systems: the particular shape and type of installation did not allow the use of the standard jointing systems of gravity sewer pipes with male/female or coupling.

Among all the available solutions, the choice fell on the second generation ECOPAL 2.0 corrugated polyethylene pipe in class SN8. We supplied 49 bars ND/ID 500 (OD 580 mm) of 3 m with flanges at the ends. In our Special Pieces Workshop, we welded 20 mm thick polyethylene flanges to the ends of the bars. Each bar has an indicative weight of 50 kg (flanges included) and a weight that allows the handling and installing of the entire system in such a narrow place. We also made the elbows with particular angles to follow precisely the tunnel path and special pieces for connection to the sewer network downstream and upstream of the stretch under intervention.

Compared to the demolition times of the pre-existing works and the installation of the supports, the laying times of the ECOPAL 2.0 corrugated pipes were relatively quick also thanks to the connection method using EPDM flanges, bolts and gaskets.

In a second moment, it has been done the connection between the square and the above tunnel.  The main pipe was drilled with a simple cutter, and ND/OD 160 PVC pipes were inserted through a seal and a special piece.