Federico Agliardi

Key Issues in Rock Fall Modeling, Hazard and Risk Assessment for Rockfall Protection

Rockfalls pose a significant threat to life and property, thus rockfall protection is a major issue in areas exposed to severe rockfall hazard. Rockfall protection approaches include quantitative rockfall hazard and risk assessment, as well as the design of structural countermeasures. These require a sound and robust quantification of 3D rockfall trajectories, distribution and intensity of impacts, and magnitude and variability of involved dynamic quantities. Providing highly reliable modeling inputs to rockfall protection remains a difficult task, because of the complexity and intrinsic stochastic nature of rockfall physics and the uncertainty of all the relevant parameters. However, significant advances in rockfall analysis have been made in the last decade, and modern 3D rockfall modeling techniques now provide effective tools to support rockfall protection activities, even in difficult design conditions. Nevertheless, their use can still be complex and raises a series of difficult steps both in the modeling and the analysis of the results. In this paper, we provide an overview of rockfall analysis aspects relevant to rockfall protection, as well as examples of applications of modern 3D rockfall runout modeling techniques in rockfall hazard and risk assessment, and countermeasure selection, design and optimization.

Long-term evolution and early warning strategies for complex rockslides by real-time monitoring

The potential of long-term, real-time surface displacement monitoring by ground-based radar interferometry (GB-InSAR) to improve the understanding of mechanisms and set up objective early warning criteria for complex rockslides is explored. Monitoring data for a rockslide in the Central Italian Alps, collected since 1997 by ground-based and remote-sensing techniques, are examined. A unique 9-year continuous GB-InSAR monitoring activity supported an objective subdivision of the rockslide into “early warning domains” with homogeneous involved material, mechanisms and sensitivity to rainfall inputs. Distributed GB-InSAR data allowed setting up a “virtual monitoring network” by a posteriori selection of critical locations representative of early warning domains, for which we analysed relationships among rainfall descriptors and displacement rates. The potential of different early warning criteria, depending on the instability mechanisms dominating different domains, is tested. Results show that (a) rainfall intensity-duration-displacement rate relationships can be useful tools to predict displacements of “rainfall-sensitive” rockslide sectors, where clear trigger-response signals occur, but are unsuitable in rockslide domains affected by the long-term progressive failure of the rock slope and (b) effective early warning strategies for collapse scenarios (entire rockslide, specific domains) can be enforced by modelling real-time, high-frequency GB-InSAR data according to the accelerated creep theory.

The First International Workshop on Warning Criteria for Active Slides: technical issues, problems and solutions for managing early warning systems

Early warning systems (EWSs) rely on the capacity to forecast a dangerous event with a certain amount of advance by defining warning criteria on which the safety of the population will depend. Monitoring of landslides is facilitated by new technologies, decreasing prices and easier data processing. At the same time, predicting the onset of a rapid failure or the sudden transition from slow to rapid failure and subsequent collapse, and its consequences is challenging for scientists that must deal with uncertainties and have limited tools to do so. Furthermore, EWS and warning criteria are becoming more and more a subject of concern between technical experts, researchers, stakeholders and decision makers responsible for the activation, enforcement and approval of civil protection actions. EWSs imply also a sharing of responsibilities which is often averted by technical staff, managers of technical offices and governing institutions. We organized the First International Workshop on Warning Criteria for Active Slides (IWWCAS) to promote sharing and networking among members from specialized institutions and relevant experts of EWS. In this paper, we summarize the event to stimulate discussion and collaboration between organizations dealing with the complex task of managing hazard and risk related to active slides.

Rock Mass Characterization by High-Resolution Sonic and GSI Borehole Logging

We investigate the relationships between the in situ P-wave velocity (Vp) of rock masses, measured by borehole acoustic logging, and their Geological Strength Index (GSI), to support a reliable assessment of equivalent continuum rock mass properties at depth. We quantified both Vp and GSI in three deep boreholes drilled in a crystalline core complex of the central Italian Alps. The boreholes were driven up to 400xa0m in depth and provided high-quality drill cores in gneiss, schist and metasedimentary rocks with variable lithology. Geological and geomechanical logging was carried out for over 800xa0m of cores, and acoustic logging was performed for more than 600xa0m of borehole length. High-resolution core logging in terms of GSI was obtained using an original quantitative approach. Candidate empirical correlation functions linking Vp and GSI were tested by a two-step statistical analysis of the experimental dataset, including outlier removal and nonlinear regression analysis. We propose a sigmoid Vp–GSI equation valid over a depth range between 100 and 400xa0m. This accounts for extremely variable lithological, weathering and rock mass damage conditions, complementing existing shallow-depth approaches and showing potential for practical applications in different engineering settings.

3D numerical analyses for the quantitative risk assessment of subsidence and water flood due to the partial collapse of an abandoned gypsum mine

After the abandonment occurred in the 70s, the mining system (rooms and pillars) located in S. Lazzaro di Savena (BO, Italy), grown on three levels with the method rooms and pillars, has been progressively more and more affected by degradation processes due to water infiltration. The mine is located underneath a residential area causing significant concern to the local municipality. On the basis of in situ surveys, laboratory and in situ geomechanical tests, some critical scenarios were adopted in the analyses to simulate the progressive collapse of pillars and of roofs in the most critical sectors of the mine. A first set of numerical analyses using 3D geotechnical FEM codes were performed to predict the extension of the subsidence area and its interaction with buildings. Secondly 3D CFD analyses were used to evaluated the amount of water that could be eventually ejected outside the mine and eventually flooding the downstream village. The predicted extension of the subsidence area together with the predicted amount of the ejected water have been used to design possible remedial measurements.

Folded fabric tunes rock deformation and failure mode in the upper crust

The micro-mechanisms of brittle failure affect the bulk mechanical behaviour and permeability of crustal rocks. In low-porosity crystalline rocks, these mechanisms are related to mineralogy and fabric anisotropy, while confining pressure, temperature and strain rates regulate the transition from brittle to ductile behaviour. However, the effects of folded anisotropic fabrics, widespread in orogenic settings, on the mechanical behaviour of crustal rocks are largely unknown. Here we explore the deformation and failure behaviour of a representative folded gneiss, by combining the results of triaxial deformation experiments carried out while monitoring microseismicity with microstructural and damage proxies analyses. We show that folded crystalline rocks in upper crustal conditions exhibit dramatic strength heterogeneity and contrasting failure modes at identical confining pressure and room temperature, depending on the geometrical relationships between stress and two different anisotropies associated to the folded rock fabric. These anisotropies modulate the competition among quartz- and mica-dominated microscopic damage processes, resulting in transitional brittle to semi-brittle modes under P and T much lower than expected. This has significant implications on scales relevant to seismicity, energy resources, engineering applications and geohazards.

Inherited and Active Tectonic Controls on the Piz Dora DSGSD (Val Müstair, Switzerland)

We analysed the Piz Dora deep-seated gravitational slope deformation by integrating field surveys, 3D structural analysis and numerical modelling. The DSGSD affects meta-sandstones, meta-conglomerates and phyllites of the Austroalpine S-Charl cover nappe, involved in a slope-scale, WNW trending closed anticline fold. The area is seismically active and experienced extensive glaciation during the LGM. The slope is affected by spectacular gravitational morpho-structures (double-crested ridges, scarps and counterscarps) associated to the deep-seated sliding of 1.85 km3 of rock along a basal shear zone up to 300 m deep. The DSGSD deformed recent periglacial features and partially collapsed. Finite-Element modelling suggests that earthquake shaking and related damage may have enhanced the triggering role of postglacial debuttressing, suggesting the importance of active tectonic conditioning in relevant alpine sectors.

Numerical investigation of the long-term influence of seismicity on the development of the Piz Dora DSGSD (Val Müstair, Switzerland)

The Piz Dora deep-seated gravitational slope deformation (DSGSD), located in Val Mustair (Eastern Switzerland), involves Austroalpine meta-sandstones, meta-conglomerates and phyllites folded into a slope-scale closed anticline. The surrounding area underwent significant deglaciation after the Last Glacial Maximum (LGM) and is subject to active tectonic uplifting and seismicity. While geological structure likely constrained DSGSD kinematics and size, the contribution of seismicity to rock slope instability in a deglaciating valley setting remains unclear.

Analysis of Rockfall Individual Risk at the Feifeng Underground Caves (Zhejiang Province, China) by Using 2D and 3D Runout Models

The Feifeng Mountain tourist resort is famous for the ancient caves and drifting activities along the Yongan River. Because of steep slope, lithology (tuff overlying a thick soft layer), tectonic structure, and the underground excavation in ancient times, the area is seriously affected by rockfalls. A quantitative rockfall individual risk assessment has been performed, by using either a 2D and a 3D modelling approach. The 2D approach results in an overestimation of risk along the a priori defined paths, due to the impossibility to consider lateral spread of rockfall trajectories. The 3D approach allows for simulating the lateral dispersion and the trajectories along convergent topography, locally increasing the Individual Risk level.