Primus Line completes seismic relining
Primus Line has provided the liners for the timely rehabilitation of two sections of an Italian water main delivering 22 million m3 of drinking water each year. The sections used Primus Liner® DN 250 PN 30 and Primus Liner DN 300 PN 25, selected based on bar pressures they needed to be able to withstand.
The Nuovo Scillato water main is one of the main drinking water conduits of the Sicilian Province of Palermo and the coastal municipalities east of the city. Built in the 1980s to supplement and reinforce the old Vecchio Canale Scillato system, it transports water from four springs from Mount Fanusi near Madonie, at a variable flow rate of 500-1,000 L/s, delivering an average annual volume of approximately 22 million m³ of water.
The main’s conduit is made of DN 900 steel pipes with a total length of 62 km and was designed to convey up to 1,000 L/s. As a result of seismic activity in 2003, the localities of Burgitabus, Cerda, and Scacciapidocchi, Termini Imerese, along the valley of the Imera Settentrionale River have experienced slow landslide movements, primarily affecting areas with outcrops of Argille Varicolori clay.
Over the years, this has led to repeated and increasingly frequent episodes of pipe damage that have resulted in service interruptions. The drought of the past two years and problems with the Rosamarina Dam, which supplies over 30 million m3 of water annually to Palermo, has considerably reduced available water reserves.
In January 2017, pending completion of the layout variant to avoid the landslide areas, which is estimated to take at least two years, operator of the integrated water service of Palermo AMAP SpA acted to head off a serious water crisis and asked Danphix Srl to devise a quick provisional solution to help restore the Nuovo Scillato aqueduct back to full operation.
The sections requiring repair were pinpointed using previous knowledge of the condition of the pipeline and the ruptures in the two localities. A GPS survey of the pipeline was conducted, with its underground positioning being located by GeoRadar detection.
The data obtained showed the almost regular course of the DN 900 pipeline. The limited displacements involved meant that a hose lining installation was possible; in particular, rehabilitation of a 1,030 m section in the Burgitabus area and a 640 m section in the Scacciapidocchi area was envisaged. An aerial survey was also carried out using a drone, which made it possible to obtain orthophoto maps of the two areas involved. The design solution had to account for the flow rate to be handled, the operating pressures and the implementation time frame of the repair work.
Being a provisional repair project, the immediate goal was to convey at least 400-500 L/s from the Scillato springs, thus allowing the recovery of an annual volume of about 15 million m3, which is approximately 15-20 per cent of the volume used by the City of Palermo’s system as a whole.
The choice of the hose lining technique in both sections of the pipe arose from the need to achieve an integral conduit flexible enough to absorb landslides; steel tube replacement was excluded due to past experience and the timeframe of the work. Regarding the pipe material to be used, given pressures of 25-30 bar and diameter requirements, a careful market study narrowed the choice down to the Primus Line, a flexible pipe produced by German company Rädlinger Primus Line GmbH.
The Primus Line combines the flexibility and extreme lightness of the textile sheath with the strength of steel tubing. These properties are obtained by using seamless-woven Kevlar® fabric and a dual-component plastic coating applied to the sheath, which is proofed against fluid egress on the inside and abrasion on the outside.
The diameters of the Primus Line system were chosen to suit the two repair sections. In the Burgitabus stretch, three Primus Liner DN 250 PN 30 liners were used. In the Scacciapidocchi section, the diameter of the three liners was increased to Primus Liner DN 300 PN 25 to account for the lower pressures.
To ensure the proper operation of the repair sections and their connection to the existing pipeline, five vent devices and four coupling caps were manufactured from specially shaped steel.
As a preliminary step, some civil works were necessary in order to prepare the work areas and to facilitate the construction of a stretch of 120 m of high density polyethylene DN 1,000 pipe casing in Scacciapidocchi, where the old steel pipe had been replaced with a DN 400 pipe.
From an operational standpoint, the works were divided into three sections: two of approximately 500 m in Burgitabus and one 640 m length in Scacciapidocchi. Access and control windows were created at the start and end points of the single sections on the existing pipe and at the positions of the five existing vents to be repaired.
After a video inspection and initial cleaning with tubular brushes, it was necessary in all three sections to work internally to remove the rough edges and burrs of the socket welded joints of the pipes. In addition, video inspections revealed some critical areas of landslide damage in the DN 900, which necessitated the baring and realignment of the pipe with the insertion of short butt-welded steel sleeves.
For each individual section, the three liners were inserted in a single operation and the three transport reels with the coiled liner were positioned one after the other. The liners were securely fastened to each other with tape prior to insertion into the existing pipe, with care taken to keep them in a uniform position along the whole stretch.
At the same time, the special steel parts for coupling and venting were manufactured; targeted quality control procedures were performed both during production and installation of the couplings. PN 40 flanged manifolds were used for the joints between the Primus Line and the steel vents and coupling pieces.
At the position of the vents, solid joints were installed between the new pieces and the DN 900 pipe by creating supportive steel structures, which were welded to the existing pipe so that in the case of a landslide the tube would not come into direct contact with the steel parts.
The outcome of the preliminary air leakage test confirmed the correct position of the tubes inside the existing pipe, subject to some adjustments. Pressurised water was then pumped into the repaired parts; the conduits were subsequently cleaned and disinfected.
The Nuovo Scillato water main is now back in operation. The preliminary civil works for the relining began on 24 February 2017, while the supply and installation of the Primus Line began on 15 March 2017. Works were completed on 12 April 2017.
Primus Line says in terms of hydraulic engineering, this is one of the most important rehabilitation projects ever performed with Trenchless Technology in Italy.
This article was featured in the Fall edition of Trenchless International. To view the magazine on your PC, Mac, tablet, or mobile device, click here.
For more information visit the Primus Line website.
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