PSI - Issue 84

Enrico Mittiga et al. / Procedia Structural Integrity 84 (2026) 867–873

872

3.5. Analysis of Transient Phases and Casting Technology

As already mentioned, from a structural point of view the most critical phase is the placement of the filling concrete. Self-compacting concrete, while offering clear advantages in terms of filling capacity and final quality, exerts significant hydrostatic pressure on the precast lining, especially if the pouring is not adequately controlled in terms of speed and filling height. For this reason, a five-stage pouring procedure was defined to limit pressures acting on the elements and modulate them appropriately. The self-compacting concrete is injected through dedicated openings at different heights on the elements, allowing for controlled distribution of the material and reducing the risk of load concentrations. The final stage involves completing the top of the arch, which is constructed using temporary steel formwork that is subsequently removed. Adjustable reaction systems consisting of M30 steel screws have been installed at the injection points, allowing the deformation of the panels to be controlled during casting and prompt intervention in the event of abnormal behaviour. 3.6. Installation and Geometric Control The precast elements are installed using a specially designed mechanical device that can operate in the confined spaces of the tunnel while ensuring precise positioning of the elements. The equipment allows the element to be lifted, rotated and guided into its final position, where it is mechanically connected to the previously installed element. Continuous topographic monitoring is carried out during all stages of assembly, allowing the correct positioning to be verified and any deviations from the specified tolerances to be corrected immediately. 3.7. Full-Scale Testing and Procedure Optimization A fundamental aspect of the work is represented by full-scale tests carried out in a dedicated test field set up at the prefabrication plant (Fig. 5).

Fig. 5. Full-scale testing.

These tests have allowed direct observation of the system's behaviour during the various assembly and casting phases, providing essential information for optimizing construction procedures: • Verify the deformation behaviour of the elements during the various casting phases.