PSI - Issue 84

Marialorenza Vescovi et al. / Procedia Structural Integrity 84 (2026) 1063–1070

1064

Keywords: Masonry tunnel linings; Structural assessment; Finite element modeling; Nonlinear analysis; Arch thrust line; Tunnel Refurbishment.

1. Introduction The structural assessment of historical masonry tunnels presents unique challenges, primarily driven by significant uncertainties. The guidelines for the 'Existing Tunnels Risk and Safety Evaluation and Monitoring System Installation' in MIMS (2022) establish a standardized approach for assessing tunnel safety, planning subsequent rehabilitation Italian works based on a preventive, risk-oriented maintenance strategy. The assessment process is subdivided into four levels: basic data collection (Level 0), defect evaluation (Level 1), risk scoring and inspection planning (Level 2), and finally, preliminary (level 3) and detailed (level 4) safety assessment and mitigation design for higher-risk sections. However, performing a detailed quantitative safety assessment on historical masonry tunnels presents unique challenges, primarily driven by significant uncertainties. For infrastructure built in the early 20th century, original design documentation is often scarce or entirely lost. Furthermore, construction practices of the period frequently relied on an adaptive approach: lining thickness and masonry type were often modified during construction to suit varying geotechnical conditions, rather than strictly following a standardized blueprint. Consequently, these structures are characterized by a high degree of heterogeneity, where brick and stone masonry may alternate, and sidewall geometries vary to counteract local asymmetrical loads. Given this inherent variability, theoretical assessments based on standard cross-sections often prove unreliable. Methods for accurately evaluating the safety of masonry tunnels under these conditions remain a relatively unexplored field. To address this gap, this paper proposes a specific evaluation procedure for the safety assessment of masonry structures, relying on a simplified analytical approach rooted in historical design practices but updated through in-situ calibration. 2. Case study The Giovi Tunnel (along the A7 Genoa-Milan motorway) was selected as a case study for the application of the proposed method. Built in the 1930s as part of the Italian infrastructure plan, the tunnel is 907 m long, as shown in Pini, G.1936. To address the lack of design data, a widespread testing campaign was conducted. On-site inspections confirmed the heterogeneous nature of the structure, reflecting the construction practices of the time. Solid clay brick masonry was used for areas where medium-stress was expected, while stone masonry was chosen for higher loads. Furthermore, sidewall thickness was increased in specific sections to withstand asymmetric pressures from the slopes above. The analysed cross-section, approximately 9 m high and 10m wide, was chosen because it has undergone no rehabilitation works, allowing the lining to be studied in its original, undisturbed condition. Exploiting the symmetry of the problem, only a half-section of the tunnel was modelled. 4 The intrados of the tunnel were mapped using laser scanning, while endoscopic surveys determined the lining thickness and material stratigraphy. Mechanical characterization included uniaxial compression tests on extracted brick cores and micro-drilling resistance tests for mortar. Moreover, the in-situ state of stress was measured using flat jack tests, while double flat-jack tests provided the elastic modulus and compressive strength. Geotechnical properties were derived from core samples extracted from the adjacent tunnel. All the properties of the materials were previously collected and discussed in Alessio, C. et al. (2024a) and Alessio, C. et al. (2024b). The properties of masonry and soil are summarized in Table 1.