PSI - Issue 84

I. Vangelisti et al. / Procedia Structural Integrity 84 (2026) 1247–1254

1251

Table 3 – Definition of the coefficients for the evaluation of levels of knowledge. ID Parameter Weight LC1

LC2

LC3

1 2 3 4 5 6 7 8 9

As-built documentation

1.5 1.5

1 1 1 1 1 1 1 1 1 1

2 2 2 2 2 2 2 2 2 2

3 3 3 3 3 3 3 3 3 3

Tunnel excavation methods

Geometrical survey

1 2

Defects survey

Compression concrete strength

3.5

Flat jack tests

2 2 2

Georadar

Video endoscopic inspections

Previously rehabilitation interventions

1.5

10 11

Exceptional events

1

SHM data (if available)

1.5

1

2

3

Table 4 – Threshold values for the evaluation of the level of knowledge of a lining inspection segment. LC1 18 ≤ LC < 30 LC2 30 ≤ LC < 42 LC3 LC ≥ 42

3.3. Structural verification: definition and outcomes

Structural verification are developed in the critical sections . Two types of critical sections are defined: • the most stressed section of the lining inspection segment (generally one for each design section), identified on the basis of FEM modelling or methods from the literature; • sections affected by significant defects, namely those defects assessed as particularly critical by the VAL4 designer (for example, G3 and G4 defects, or defects compromising global or local structural stability). For each lining inspection segment, more than one section of this type may be identified. In addition to the verifications mentioned above, depending on specific defects scenarios, further local verifications may be carried out, with reference to scientifically validated and well-established methods. When structural verifications for either maximum stress or significant deterioration are not fullfilled, corrective actions shall be undertaken based on the obtained outcomes. In particular: • unfulfilled maximum-stress verification: a monitoring system may be adopted, as provided for by the Tunnels Guidelines, to assess the evolution of the structural behaviour of the lining. The characteristics of the monitoring system shall be described in the supplementary documentation attached to the VAL4. Depending on the Capacity-to-Demand ratio obtained in the VAL4 and/or on the monitoring results, the need for designing an appropriate intervention shall be evaluated. During the time interval between the design and execution of the intervention, the monitoring system results shall provide indications on whether additional compensatory measures are required or not; • unfulfilled significant defects verification: a detailed investigation of the defect is recommended, leading to the development of a final intervention design to be included in the supplementary documentation attached to the VAL4. Before the implementation of the final intervention, the need to adopt temporary protective measures and/or interventions in the affected area shall be assessed. 4. VAL4 procedure for lining inspection segments with interventions The objective of VAL4 for ispection lining segments with interventions is to verify the structural capacity, durability, and robustness, and consequently to assess whether an extension of their nominal service life is possible or, alternatively, whether compensatory measures are required. Before assessing the possible extension of the nominal