PSI - Issue 84

Nicola Perilli et al. / Procedia Structural Integrity 84 (2026) 813–820

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slopes and incipient landslides . The solutions include: (i) adoption of four nested spatial units and (ii) adoption of a structured workflow (Tab. 3, Fig. 1). The workflow integrates data collection across the four nested spatial units, which guide the collection of both essential and supplementary data (Perilli et al., 2025b). As summarized in Table 3 these units are: Landslide Reference Inventory Area (LIRA), Diagnostic Area (DA), Geomorphologically Significant Area (SGA), that also include the Close Zone of SGA, and the Relevant Area (RA), including Approach Zone (AZ). As depicted in Figure1, essential data are collected through ground-based surveys in the AZ, RA and the Close Zone of SGA. Supplementary data, derived from back-office analysis and remote sensing of DA and SGA. These refinements and solutions ensure that thematic layers, susceptibility models, and field data collection are guided by an updated and operationalized procedures and tools for CdA assessment. They also promote integration of multidisciplinary datasets and support prioritization of inspections based on field evidence. Table 2 – Operational definitions of landslide-related terms according to Perilli et al. (this volume), showing differences from LLG 2020 and implications for slope-specific assessments and susceptibility classification. Key terms of LLG 2020 Key terms according to Perilli et al. ( this volume)

Represents the probability—based on geomorphological, geological, environmental, and anthropogenic context—of slopes generating landslides; focuses on areal predisposition, not slope-specific; excludes temporal probability or exact location. Therefore, represent an areal predisposition, not a slope-specific condition, and the Susceptibility Class (area) cannot be based on Slope Instability (volume). Potentially unstable slopes - Areas with high susceptibility correspond to potentially unstable slopes, where no active movement is observed but predisposing factors indicate a high likelihood of instability. This category supports preliminary identification of areas that need further investigation. Slope instability without mass movement, recognizable by precursors of slope deformation or cracks. It represents a slope-specific condition, not an areal predisposition. Ongoing gravitational movements, i.e., landslide, the degree of slope instability is evaluated using three primary parameters - P A , P V , P M - of mobilized volume. It is a slope-specific condition, showin active or past displaced materials. Defines the specific class of slope instability based on SID modulated by secondary parameters: Reliability of primary parameter estimation and Status of mitigation works. SIC class define the class of Factor of Susceptibility Class.

Susceptibility

Susceptibility

-

Potential instable slope

-

Incipient Landslides

Slope Instability Degree (SID)

Slope Instability

Slope Instability Class (SIC)

Susceptibility Class

Potential Landslides Removed This solution eliminates sources of operational inconsistency, ensuring P A , P V , P M are applied only to actively moving slopes. The use of the incipient landslide category provides an intermediate classification for early detection, while highly susceptible areas can still be identified through remote or field analyses Table 3. Conceptual and operational roles of nested spatial units, with their respective spatial extents, for identifying landslide–bridge interactions and assessing primary and secondary parameters (modified from (Perilli et al. 2024a, 2025b) Area Conceptual Role and Operational Practical Role LIRA Inventory area of previously mapped landslides; supports characterization of geomorpho-lithological context and estimation of primary parameters. DA Broader morpho-tectonic setting where potentially unstable slopes and incipient or active landslides affecting the enclosed SGA are surveyed; includes physiographic, lithological, and land-use context. Potential instabilities must be systematically identified via remote sensing. Maximum extent : 3 × 3 to 4 x 4 Km.; SGA Area where topographic, litho-tectonic, hydrographic, and anthropogenic factors, as well as incipient or active processes affecting or threatening the RA, are characterized and surveyed. Focuses on upslope and downslope bridge sectors; remote sensing analysis followed by field verification to map precursors or active landslides. Maximum extent : 1,2 × 1,2 to 2,2 x 2,2 Km. RA Area where topographic, litho-tectonic, hydrographic, and anthropogenic factors, as well as incipient or active processes affecting or threatening the RA, are characterized and surveyed. Focuses on upslope and downslope bridge sectors; remote sensing analysis followed by field verification to map precursors or active landslides. Maximum extent: 500-600 to 700-800 m.