Valerio De Biagi

Accurately predicting the consequences of geohazards remains a major challenge in quantitative risk assessment. Public and private stakeholders often face difficulties in defining risk management strategies, prioritising interventions, and allocating resources for mitigation, particularly in the case of rockfall hazards, where ensuring resilient infrastructure and safe communities is increasingly urgent. Building on a quantitative risk assessment framework previously developed by the authors, this study presents an enhanced methodology that integrates a new fragmentation model for propagation analysis. Understanding the size and energy of blocks potentially impacting elements at risk is crucial for the accurate design of protective systems and the estimation of their probability of failure, enabling a more realistic assessment of residual risk. Consequences are analysed across both social and economic dimensions. By capturing the interplay between hazard dynamics, infrastructure vulnerability, and the effectiveness of protective measures, the proposed framework supports the development of safer and more resilient transport networks in rockfall-prone areas, and it serves as a robust decision-support tool for policymakers and public authorities. The method is applied to viable infrastructure exposed to rockfall, such as high-traffic or mountainous roads that often serve as the sole access routes to remote areas.

Flexible rockfall barriers are widely adopted passive protection systems in mountainous regions, yet their design still relies on deterministic criteria based on Maximum Energy Level (MEL) and Service Energy Level (SEL) tests. These standardized procedures provide a single nominal energy value, which does not reflect the variability of real impact scenarios nor the stochastic nature of barrier performance. This limitation hinders the integration of reliability-based principles into design, a cornerstone of modern structural engineering. This work merges a probabilistic framework to estimate the mechanical performance of flexible rockfall barriers under a wide range of impact scenarios into the RockStop software, integrating the resulting capacity curve within the software and enabling its practical use in design workflows. The framework derives capacity curves for flexible rockfall barriers and is built upon a generalized multi-component analytical model, developed by the authors, that simulates barrier response under arbitrary impact conditions by assembling analytical representations of each component (net, wire ropes, posts, energy dissipators). A Monte Carlo simulation scheme propagates uncertainties in geometry, mechanical properties, impact position, and component variability, generating a probabilistic description of the barrier’s energy absorption capacity. Results show that highly eccentric impacts can significantly alter the nominal capacity. The integration of trajectory outputs, combined with the barrier capacity curve, in RockStop enables site-specific assessment of all possible actions and their frequency, allowing the calculation of failure probability for both newly installed and existing barriers. This framework marks a major advancement toward risk-informed design by enabling the integration of reliability-based safety formats for rockfall barriers, supporting comprehensive lifecycle performance assessment, and providing a robust basis for quantifying residual risk after mitigation.

Reinforced earth embankments represent a robust solution for rockfall mitigation, yet their dynamic response under high-energy impacts remains poorly documented. This study presents a unique full-scale impact test performed on a 6.75 m-high reinforced earth embankment composed of nine layers of granular material reinforced with double-twisted hexagonal mesh (DT mesh). The test involved a standardized block (EAD 340059-00-0106:2018) impacting below the first reinforcement layer with an energy of approximately 10 MJ, simulating an extreme rockfall event. The novelty of this work lies in the advanced multi-sensor monitoring system integrated into the embankment and the block. The embankment was instrumented with tri-axial and mono-axial accelerometers positioned across different layers and laterally to the impact zone to capture the propagation of dynamic loads and the volume of disturbed material. A custom-designed network of strain gauges was embedded within the reinforcement layers to monitor tensile forces, while load cells at the foundation recorded stress transmission during the impact. Additionally, the impacting block was equipped with a gyroscope and accelerometer to track its kinematics. High-speed cameras captured the impact sequence, enabling correlation between visual observations and sensor data. Preliminary results reveal the distribution of acceleration peaks within the embankment, the volume disturbed by the impact, and the foundation load response under dynamic conditions. The combined dataset provides unprecedented insight into energy dissipation mechanisms and deformation patterns in reinforced earth structures under extreme impacts. This experiment establishes a benchmark for validating numerical models and improving design guidelines for embankments used in rockfall protection. The integrated monitoring approach offers a powerful tool for understanding structural resilience and optimizing reinforcement strategies under high-energy impact scenarios.

Recent research on the progressive collapse of buildings has mainly focused on load redistribution following member failure, commonly referred to as “re-distributional progressive collapse”. However, “impact-type progressive collapse” remains less explored. This mechanism, often triggered by dynamic events such as falling debris or fire scenarios, introduces complex interactions that are difficult to capture using traditional quasi-static models, leaving a significant gap in our understanding of how impact-type progressive collapses occur. This study aims to bridge that gap by investigating the impact forces generated between concrete bodies of various geometries through an experimental campaign. Spherical, semi-spherical, and cubic concrete samples were dropped onto a fiber-reinforced concrete plate from controlled heights. A high-speed camera captured the impact for detailed analysis, while parameters such as impactor mass and velocity, contact radius, and concrete compressive strength were systematically varied. Using advanced data processing techniques, namely Variational Mode Decomposition (VMD), results showed that a 73% increase in impact velocity led to a 75% rise in maximum contact force. Geometry had a significant influence, with spherical and semi-spherical specimens generating up to 64% higher forces than cubes of equal mass. In contrast, compressive strength had a minor effect, raising contact force by only 9% despite a 50% strength increase. High-speed camera footage confirmed more concentrated impacts for spherical shapes, while no notable differences were found between spherical and semi-spherical specimens of equal weight but different contact radii.

This research addresses key challenges in progressive collapse prevention by introducing an advanced method to enhance the complex structural systems monitoring. The study focuses on variation of deformation work patterns with the aim to identify the most critical load paths while a random element within the structure undergoes damage. A comprehensive mathematical model has been developed to analyze changes in load paths due to damage in structural elements. The method utilizes an energy-based metric introduced by De Biagi and Chiaia, allowing for a detailed assessment of damage progression. The damage is simulated through the alteration of the stiffness of structural elements by applying progressive cross section reduction. The predictions of the model were validated through its application to simple systems composed of rods, where changes in load paths were observed as damage advanced in random elements. For more complex structural systems, the method was applied using numerical simulations, providing a detailed evaluation of its performance in more load cases scenarios. The proposed metric effectively captures the effects of localized damage and its propagation through the system, offering valuable insights for the monitoring and prevention of progressive collapse. The method yields two significant outcomes: first, mapping the variation of deformation work with respect to the damage allows for the visualization of the variation in the load path during the damage of a random element within the structure, thus, identifying which elements are loaded and which are unloaded; second, the study of evolution of the variation of deformation work with respect to the damage for different stiffnesses allows identifying the value of critical stiffnesses that determine whether the element remains part of the main load-bearing path. In this work, the method is applied to 2D and 3D truss systems, which are representative of critical infrastructure like bridges and towers, as well as to ad hoc designed structural schemes created to highlight specific aspects and demonstrate the effectiveness of the method. The aim of the method is not only to ensure the safety of vital infrastructure by improving resilience against catastrophic events, but also to offer practical insights by identifying the most critical areas for sensor placement, enabling optimal monitoring and early detection of failure points.

Anti-submarine (ASM) ring nets are fundamental components for various passive solutions to mitigate rockfall hazard. While numerical models could accurately assess their performance for all the applications, the modelling of a whole system comprising the net is time-consuming. An analytical model of wire ring nets currently on the market, applicable to the different configurations, can thus represent a profitable tool to investigate the performance of nets used in retaining systems. Currently, for flexible rockfall barriers the whole system structural behaviour is evaluated with real tests impact tests performed in the centre of the system, only, possibly overestimating the system capacity and consequently underestimating the residual risk at installation sites. An analytical model is proposed in this paper with the aim to evaluate the mechanical behaviour of wire ring nets for eccentric impacts too. The model validation is performed using quasi-static experimental punching tests results related to both rigid and flexible boundaries conditions for the centred impact case, while numerical models, realized applying well-established approaches, strengthen the model validation for eccentric impacts. Analyses performed during the barrier design phase and its service life enable to assess the real efficiency of retaining systems.