PSI - Issue 84

Gerardo Sorrentino et al. / Procedia Structural Integrity 84 (2026) 1071–1078

1076

(a) (b) Figure 3 (a) STW method equivalent loading body and soil failure mechanism (b) STW method lining external loads scheme

3. Case study The two methods have been applied to the Giovi tunnel, a masonry structure built in the 1930s within a major infrastructure program launched under the Fascist regime. The tunnel is now part of the A7 Genoa–Milan motorway, a key highway for heavy traffic directed to the Port of Genoa. The tunnel is 907 m long, with a carriageway about 10 m wide and a height of roughly 9 m. Field inspections revealed that the masonry lining consists of stone blocks or brickwork, selected to suit local geological conditions and the expected loads. The tunnel construction followed the Belgian method, with excavation starting from the top of the tunnel's cross-section. The vault was constructed first, followed by the sidewalls (one at a time) and, lastly, the invert. Some sections showed asymmetric shapes, with one sidewall thicker than the other, probably due to the slopes above the tunnel. The tunnel was deeply investigated by in-situ measurements (as described in Alessio et al., 2024a, 2024b). Geotechnical investigations showed that the area is mainly composed by clayey soils, satisfying the criteria set out by the formulations of Kommerell and Desimon. Due to the lack of the original archival material on design and construction methods regarding the case study, the evaluation of the soil design loads had to rely on some assumptions. Within this framework, considering the approaches of Kommerell (1912) and Desimon (1939), a soil overburden of 24 m was assumed. This value was used for both approaches to allow better comparisons. According to the classification of Desimon (1939), the coefficient for the horizontal forces f for scaly clays was taken as 0.8. To validate the historical design models, the stresses measured by means of flat-jacks were employed. This semi destructive technique is widely recognized in heritage masonry assessment for its ability to provide a direct measurement of the current compressive stress state (in-situ stresses). It is important to highlight that the flat-jacks provide a measurement of the average stresses for the limited depth of the instrument (around 30 cm), and do not provide a stress measurement for the whole section of the masonry lining (which varies from 1.20 m at the keystone, and 1.35 at the base). One reference section of the tunnel, surveyed by means of laser scanner, was selected for the design methods comparison.