Monitoring of Stray Current Interference in the Reinforced Concrete Structures of the Turin Underground Railway Loop

Briglia, Maria Cristina (Cescor srl) | Bazzoni, Bruno (Cescor srl) | Cavallero, Giovanni (Italferr SpA) | Melodia, Domenico (Italferr SpA) | Panaro, Francesco (Recchi SpA)

OnePetro 

ABSTRACT The town of Turin represents an important railway junction in North Italy. Starting from beginning of nineties, the main railway lines which originally ran on surface through the town, have been deeply revamped and transferred underground, returning a huge green area to the town and reducing the traffic on surface. Significant civil works have been needed, performed in a very crowded urban area, to create a railway underground loop several kilometers long, consisting of up to three parallel tunnels located on two levels underground and with railway stations distributed along the route. All the concrete structures are exposed to DC stray currents coming from the new underground railway lines and from pre-existing lines on surface. Together with some interventions performed to minimize stray currents and their effects, a monitoring system has been designed and installed, with permanent reference electrodes embedded in the concrete structures at critical location. The paper illustrates the design of the monitoring system, the methods and criteria adopted. Results obtained in the commissioning phase are reported. INTRODUCTION The Turin Railway Loop (TRL) is a series of railway lines crossing the town of Turin, which is an important railway junction in North Italy, and running almost completely underground. The work started in June 1992 and included several phases and different activities: -revamping of existing facilities; -transfer underground of most of the existing lines and cover of cuttings; -construction of new lines underground; -construction of new underground stations along the loop. An important benefit of the project, apart from the fictional improvement for the railway system, was to return a huge green area to the town and to reduce the traffic on surface. The civil works of the TRL, completed in 1997, had a total length of 4,580 km, all located in a very crowded urban area (see Figure 1). They included: construction of vertical reinforced concrete walls; soil strengthening with micro piles; covering of cuts with reinforced concrete beams, most of which prestressed. Because of the complexity of the project, with the adaptation of the new structures to the old ones, several types of cross sections are met (see Figure 2), consisting of up to three parallel tunnels located on two levels underground and with railway stations distributed along the route. All the concrete structures of the TRL are exposed to DC stray currents: in Italy, the railway system is fed by DC current (3000 V).

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