The 8.7-km-long exploratory tunnel of Saint-Martin-de-la-Porte was excavated along the future southern tube of the Lyon-Turin railway line tunnel using a TBM with a cutter head of 11.26 m in diameter through the geological formation known as "Houill & egrave;re Brian & ccedil;onnaise". The temporary precast segmental lining, composed of segments 1.50 m long and 45cm thick, made of C45/55 and C80/95 concrete, will be integrated with a reinforced cast in-situ concrete final lining. The excavation of a geological formation characterized by high convergences and the dual function of the tunnel (short/long term) required a segmental lining design and production adopting a high-quality control procedure, such as the implementation of an adequate system of traceability of the segments. All the tunnel excavation works and the construction of the segment plant, built through the refurbish of an old sawmill, represented a virtuous example of industrial design and production based on high sustainability criteria.
The original design for the primary lining system for Driskos Double Tunnel along the Egnatia Motorway in Greece, consisting in a PVC-P geomembrane, was foreseeing a 500 g/m(2) nonwoven geotextile as a drainage and mechanical protection layer. The nature of the rock with high pressures expected on the concrete vault as well as the huge amount of water that was encountered during excavation was making it necessary to substitute the nonwoven geotextile with a high-performance drainage geocomposite, capable to guarantee an effective drainage for the whole design life and to drain the water at 360 degrees within the plane in order to allow efficient discharge capacity even in case of concentrated water flows. The paper describes the evaluation of the design state of stress on the drainage geocomposite, the required water discharge capacity and the waterproofing performances that were bringing to the choice of the best technical solution. After almost 20 years in service, the lining system is working properly and no major problems have been encountered.
The need for transition towards alternative and sustainable solutions in the tunneling sector is underscored by global data. Italy ranks second worldwide in both the number and length of tunnels, following China, with many surpassing 30 years of operation. Enhancingsustainability and durability requires interventions in both materials, such as concrete and its reinforcement, and the precast concrete segmental lining production process. Partially substituting clinker with sustainable binders like calcium sulfoaluminate (CSA) cement and replacing steel with non-metallic materials such as glass fiber reinforced polymer (GFRP) can mitigate environmental impact. This paper presents a case study investigating the use of GFRP-reinforced CSA-based concrete to enhance sustainability and durability in tunnel linings.
The JV between Impresa Pizzarotti and Saipem awarded the project for the construction of the Florence by-pass tunnels for the high-speed railway Milano-Napoli. With the aim of implementing the guidelines of Environmental Social Governance and to make the production of the segments for the tunnels lining compatible with the mechanized excavation work program, the JV had to choose whether to focus on a new precast plant highly industrialized, or sustainably transform an existing plant. The paper describes the process of sustainable reindustrialization of the existing prefabrication plant, located in the municipality of Lucignano, a geographical position close to the construction site of the Florence project and barycentric for future mechanized tunnel excavation works in Italy, highlighting the advantages of the conversion in terms of sustainability and, in this case, compared to the construction of a new plant. The existing plant, having a railway station less than 5 km away, allows the transport of the produced segments by rail, minimizing road transport. The prefabrication plant will produce about 50,000 segments of universal ring type with a length of 1.5 meters each and a thickness of40 cm and is organized with an automated carousel and a production process that uses computerized monitoring and tracking systems.
Dealing with time-dependent phenomena during tunnel excavation and management is a complex topic that engineers and geologists need to face worldwide. Threats to tunnel stability are posed by the swelling/creep behaviour of geomaterials. These phenomena occur during the construction of the tunnel but can evolve for a long period after tunnel operation and can jeopardize the tunnel integrity with time. Although the topic of time-dependent behaviour has been repeatedly addressed in the literature, less attention has been paid to methodologies to deal with it during the serviceability of tunnels. Therefore, appropriate and reliable methods are needed to analyse and predict tunnel behaviour during their service life and/or refurbishment processes. This paper will focus on existing tunnels subjected to the time-dependent behaviour of the surrounding ground to identify the methodological approach for designing maintenance works and/or managing the associated risks. Examples from the Authors' experience are used to support the discussion.
