GE 34/22 – SS 1 “Aurelia” – Access road network to the Port Hub of La Spezia – Variant to SS 1 “Aurelia” – 3rd lot between Felettino and the motorway link – Functional Section C (3rd functional segment), from the San Venerio interchange to the Melara interchange. Monitoring services during construction and post-construction are included.

Project objective

The project aimed to complete Section C of Lot 3 of the Aurelia Bis, along the stretch between the San Venerio interchange (north abutment of the “San Venerio II” viaduct) and the Melara interchange, connecting to the motorway link.
As part of the Detailed Design for conventional excavation tunnels, the completion of the Fornaci I Tunnel was undertaken. This section presented significant criticalities due to the undercrossing of the “Vorticosa” railway tunnel, located at an extremely reduced distance (approximately 1.5 m) between the road tunnel crown and the railway tunnel invert.
Given the complexity of the geological context and the presence of interfering railway infrastructure under highly critical conditions, the observational method was adopted in accordance with applicable technical standards (NTC 2018, § 6.2.5).
In such conditions, stress-strain monitoring of the affected structure played a key role in ensuring both safety and effectiveness of the construction activities. All automated instruments were integrated into a centralized data acquisition and transmission system, enabling real-time monitoring of measurements.
To control the stress evolution in the railway tunnel during and after the undercrossing operations, a comprehensive monitoring system was designed and installed on both the existing lining and the reinforcement structures, including:

• microprisms for high-precision topographic measurements
• pairs of extensometers (Vibrating Wire Strain Gauges)
• flat jacks for measuring circumferential stress variations in the lining
• embedded strain gauges within the reinforcement structures
• instrumentation installed on steel ribs
• microprisms for railway track monitoring, including post-construction phases

Topographic monitoring was carried out continuously using a robotic total station.
Specific Alert and Alarm thresholds were defined for each monitored parameter, both in terms of stress and deformation, in order to safeguard the integrity of the railway tunnel during construction. These thresholds were established based on expected values derived from numerical analyses and design models.
The system was configured to automatically send notifications (SMS and email) when predefined thresholds were exceeded. In particular:

• exceeding the Alert threshold triggered intensified analysis of monitoring data
• exceeding the Alarm threshold required suspension of construction activities and detailed assessment of the structural stress-strain behavior, with the potential implementation of additional mitigation measures

The project was successfully completed in full compliance with design requirements, followed by the commissioning of the railway line within the scheduled timeframe.