PSI - Issue 84

Nicola Perilli et al. / Procedia Structural Integrity 84 (2026) 805–812

809

• SI Class replacing Susceptibility Class (i.e., Suscettibilita in Fig. 1), is derived from the SI Degree further adjusted according to the following two secondary parameters (Tab. 5, Fig. 1 ). • Reliability of Primary Parameter Estimation -replaces the ambiguous term Model Uncertainty or Assessment Reliability . The two proposed options - limited and good ( limitata and buona in Fig. 1) - explicitly reflect the degree of uncertainty in the estimation of P A , P V , and P M . This provides a clear and standardized practical procedure to adjust SI Degree for assessing the SI Class accordingly ( Tabs. 5, 6 Figs. 1, 2 ). • Status of Mitigation works replaces Mitigation Works (Tabs. 5,6, Fig. 3). The here proposed two options - not involved and involved - indicate whether mitigation works are or are not affected by landslide. The SI Degree should be consistently updated for assess the SI Class accordingly ( Tabs. 5, 6; Figs. 1, 2 ). • Potential Landslide is removed (Tabs. 2, 5). Consequently, the associated parameter P C - Criticality Level – i.e., grado di criticita , (Tab. 2) is also removed, and the SI Degree is no longer evaluated for it. The qualifier potential is retained only for potentially unstable slope corresponding to areas classified as highly susceptible. Table 5. Comparison of LLG 2020 terminology with the proposed refined framework. LLG 2020 Term This Work Operational / Methodological Consequences ( this work )

Quantitative measure of actual slope conditions; directly calculated from P A + PV + PM; the use of degree reduces ambiguity with Class. Derived from SI Degree; modulate by secondary parameters - Reliability of primary parameter estimation and Status of Mitigation works; the use of class is coherent with Class of Factor of Susceptibility . Reflects inspector confidence in P A , P V , P M ; reduces arbitrariness; provides standardized operational guidance; enhances reproducibility. Explicitly considers whether mitigation works are involved or not in the landslide phenomenon; increases transparency in updating the SI Grade; and reduces interpretative inconsistencies. Eliminates ambiguous key term improves conceptual clarity; improves methodological robustness, namely the Potential Landslides-based Slope Instability is no longer evaluated. Removing Criticality Level (PC); prevents inconsistent application; supports clear operational rules; reduces arbitrariness in slope classification.

Slope Instability (SI)

SI Degree

SI Class

Susceptibility Class

Model Uncertainty / Assessment Reliability

Reliability of primary parameter estimation

Status of Mitigation works

Mitigation Measures

Removed

Potential Landslides

Removed

Criticality Level

Table 6 Decision Rules for secondary parameter used to evaluate Slope Instability Class

Reliability of primary parameters estimation

When the inspector is uncertain in estimating 2 or 3 primary parameters

the SI Degree is elevated to the next class

When the inspector is confident with the primary parameters evalution or is uncertain in estimating P A o di P V Status of Mitigation Work When the inspector identifies partial or full involvement of mitigation works by the landslide phenomenon, When the inspector does not detect any involvement of mitigation works within the landslide body, the degree of instability remains unchanged.

the SI Degree of remains unchanged

the SI Degree is elevated to the next class.

the SI Degree remains unchanged.

These refinements aim to improve landslide characterization, reduce operational ambiguities, and enhance methodological consistency in the assessment of the Susceptibility Factor, in line with LLG 2020 and the international literature.