Andrea Segalini

Terrestrial Photogrammetry and Numerical Modelling for the Stability Analysis of Rock Slopes in High Mountain Areas: Aiguilles Marbrées case

Several high-altitude slope instability phenomena, involving rock blocks of different volumes, have been observed in recent years. The increase in these phenomena could be correlated to climatic variations and to a general increase in temperature that has induced both ice melting with consequent water seepage and glacial lowering, with a consequent loss of support of the rock face. The degradation of the high-altitude thermal layer, which is known as “permafrost”, can determine the formation of highly fractured rock slopes where instabilities can concentrate. The present research has developed a methodology to improve the understanding and assessment of rock slope stability conditions in high mountain environments where access is difficult. The observed instabilities are controlled by the presence of discontinuities that can determine block detachments. Consequently, a detailed survey of the rock faces is necessary, both in terms of topography and geological structure, and in order to locate the discontinuities on the slope to obtain a better geometric reconstruction and subsequent stability analysis of the blocky rock mass. Photogrammetric surveys performed at different times allow the geostructure of the rock mass to be determined and the rock block volumes and detachment mechanisms to be estimated, in order to assess the stability conditions and potential triggering mechanisms. Photogrammetric surveys facilitate both the characterisation of the rock mass and the monitoring of slope instabilities over time. The methodology has been applied in a case study pertaining to the North Face of Aiguilles Marbrées in the Mont Blanc massif, which suffers from frequent instability phenomena. A slope failure that occurred in 2007 has been back-analysed using both the limit equilibrium method (LEM) and 3D distinct element modelling (DEM). The method has been supported and validated with traditional in situ surveys and measurements of the discontinuity orientation and other rock mass features.

Automated Inclinometer Monitoring Based on Micro Electro-Mechanical System Technology: Applications and Verification

The paper illustrates the efficiency of a novel inclinometer device by comparing results obtained from some prototypes installed in three landslides and those derived from classic inclinometers. The new device, called Modular Underground Monitoring System (MUMS) is intended to be applied for natural and artificial slope deformation monitoring and landslides dynamics control, assessment and forecasting. The MUMS instrumentation was developed from the idea of replacing the standard measurement procedure by locating nodes at known distances along a connecting cable placed within a vertical borehole. Each node measures its local orientation (related to the National Elevation Dataset (NED)) by means of a micro electro-mechanical system (MEMS) formed by a 3D digital linear acceleration sensor and a 3D magnetic sensor. This allows us to determine the direction cosines of the borehole axis in each node and calculate its 3D shape and deformation along the whole borehole. This paper compares the classic instruments and the new MUMS device, with evidence of the advantages of measurement automation and economy in the use of the proposed device, which could also be equipped with other electronic instruments that would allow the measurement of other interesting physical quantities (i.e. pore pressure, temperature, stresses etc.) together with displacement components. The comparison is carried out through the examination of few installation in various types of landslides, with particular attention to the accuracy and repeatability of the measurements that are automatically made.

Underground Landslide Displacement Monitoring: A New MMES Based Device

This paper describes the analysis of the effectiveness and reliability of a new type of inclinometric chain, which is still under development by the authors, and is intended to be applied in the underground slope monitoring field. In the first part, the paper describes the new instrumentation which should allow for a deeper and detailed understanding of the type, location and origin of slope movements that should, in turn, help in understanding the triggering causes and the evolution mechanisms of landslides, and provide an innovative and substantial contribution to their stability analysis and control. The second portion of the paper is dedicated to a comparison between the classic instruments and the new MUMS device, demonstrating the advantages of measurement automation and economy in the use of the proposed device, which could also be equipped with other electronic instruments that would allow the measurement of other interesting physical quantities (such as pore pressure, temperature, stresses, etc.) together with displacement components.

Geotechnical and Geophysical Characterization of Frozen Granular Material

Degrading or thawing permafrost has been identified as being an issue of national importance with respect to its potential for causing severe damages or even loss of lives in densely populated Alpine regions due to climate change (Gruber et al. 2004; Gruber and Haeberli 2007). On this basis, a joint study was initiated by the Safe Mountain Foundation (Fondazione Montagna Sicura, Cormayeur, Italy) and some universities to investigate variations in geotechnical behaviour of the Alpine permafrost caused by changes in temperature. Permafrost is found in the Alpine regions at elevations higher than 2,500 m above sea level, depending on the location and exposure of the slope. Its mechanical features are determined by the combined effect of ice and soil particles. The water content can have an important influence on the shear resistance of the frozen soil: if the water content is low, the ice will not be able to include the soil particles. However, if it is very high, the resistance will be determined above all by the ice itself (Andresland 1987). Temperature is another driving factor that can influence the mechanical behaviour of ice (Fish and Zaretsky 1997). On this basis, this work concentrates on analysing the geotechnical and geophysical behaviour of the dispersed moraine deposits found in Alpine areas, which have been subjected to different climatic conditions due to the effect of high temperatures. The work concentrates on the geotechnical and geophysical characterization of two different glacial deposits present in the Aosta Valley region; the first one generated by the Tsanteleina glacier (Rhemes Valley, 2,690 m a.s.l.), and the second one surrounding the Blu lake (Ayas Valley, 2,214 m a.s.l.). The characterization was carried out at different scales: laboratory-scale analysis using representative granular materials and field in situ investigations, geotechnical and geophysical testing. The geotechnical measurements were performed using photographic dimension analysis of the deposit, coupled with seismic and electrical surveys. Specimens were collected, remolded, saturated, and kept in a cooler in the laboratory. The specimens were later subjected to laboratory tests to evaluate the geomechanical strength properties of the materials using (mono-axial compressive strength and Young modulus) and geophysical (P and S wave velocities) behaviour of this kind of soils are affected by temperature variations under 0 °C (−35/−5 °C).

Assessment of stability conditions of ancient underground quarries using on-site monitoring and numerical modeling

This work, carried out by members of the University of Parma’s Department of Civil and Environmental Engineering and Architecture, analyzes the stability of the ancient underground quarries at Viggiu (Varese,Italy). The objective of the study was to verify the actual structural predisposition to instability phenomena in the ancient ornamental stone quarries for a historical and cultural valorization as well as the recovery of the Danzi and Beltrami quarries. Although completely abandoned, these sites could be used as a tourist attraction and/or as a teaching environment. They are a wonderful example of industrial architecture, presenting audacious compositions of filled-in trenches and room and pillar techniques (Hedley and Grant, 1972). With such objectives in mind, a monitoring system that aims to control the most significant joints and discontinuities of the site has been realized. A numerical model of the entire rock mass has been developed in order to analyze the stability of the underground openings. A route for visitors has also been identified.

A Factor Strength Approach for the Design of Rock Fall and Debris Flow Barriers

This paper discusses the applicability and the limitations of an approach to the limit states design of flexible barrier in which the soil/rock strength are factored as required in the European construction code. It shows as this approach has different implications if it is applied to the same kind of structure when loaded by different phenomena (rockfall and debris flow in particular). Flexible barriers are common countermeasures to protect from rockfall hazard and to restrain debris flow events. Even if an intense scientific production has demonstrated the difference between the two phenomena, the protection systems are still often designed in the same way. Additionally, the Eurocode 7 (EC7), which is the European Standard concerning geotechnical design, has not been conformed to these kinds of structures and consequently a relationship between the reliability of the system and the partial factors does not exist. Since most of the parameters that rule these systems are not even considered in the code, the Authors propose the study of two cases, in which rockfall and debris flow occur, respectively, to analyse the applicability and the limitations of EC7 principles to design the suitable kind of structure.

Study of an Active Landslide on A16 Highway (Italy): Modeling, Monitoring and Triggering Alarm

This paper presents the preliminary results of a study carried out on an active landslide, which insists on the A16 (E842) Highway, between Campania and Puglia region (South of Italy). The area lies at the foot of a large gravitational mass, classified as “ancient landslide deposit” where a system of landslides, with different types and activity states, are present. It is characterized by the widespread presence of clayey sequences that affect the stability of the slopes looming over the highway. The site has been instrumented with a series of automated sensors, both innovative and traditional, which monitor different physical entities. Furthermore, a photogrammetry survey was carried out with a drone in order to know precisely the geometry of the slope. Once the geotechnical and hydraulic parameters were collected, a 2D finite difference numerical model (FLAC® software) of the slope was set up and a series of back analysis were carried out comparing the model results with those obtained from the monitoring database. Through these back analyses, the choice of the geotechnical parameter was refined and validated. Different physical variables and results are shown into a unique representation, in comparison with the developed model and the geological and geotechnical information. Following the trends of data, the weekly/monthly average displacements and the possible causes (heavy rainfall, raising of the water table), it is possible to study the mechanical behavior of the landslide and establish preliminary warning thresholds, which have to be verified in future. The large number of acquisitions, provided by the automated monitoring system, permits to use a statistical approach in order to identify a good reliability and increase the confidence on the results. The obtained knowledge allows for the automation of the data processing procedure and for the control of the highway stability in near real time.

Joint Modelling and Monitoring on Case Pennetta and Case Costa Active Landslides System Using Electrical Resistivity Tomography and Geotechnical Data

The aim of this paper is to study the Case Costa and Case Pennetta active landslides complex in the Northern Apennines (Parma, Italy). A ground model of an active and complex landslide system in instability prone rocks, made mainly by sandstones and claystones (Scabiazza Sandstones, Ligurian Unit), is developed through an integrated approach, utilizing different monitoring tools. Some of the tools are traditional (i.e. piezometers and inclinometers) and others are innovative, such as the acquisition of electrical tomographic data in time-lapse mode (TL-ERT). The latter has many practical applications to the study of subsurface properties and processes. This approach will allow to create a model of the physical state of the complex landslides, to observe the groundwater circulation and its variation with time, by relating it to the kinematics of the landslide bodies. Results of the landslide investigation revealed that an integrated approach, centred on volumetric geophysical imaging, successfully achieves a detailed understanding of structure and lithology of a complex landslide system, which cannot be attained through the use of remotely sensed data or discrete intrusive sampling alone. This paper describes this multi-technique approach for landslide hazard assessment reporting the preliminary monitoring results; such approach seems to be applicable to other hazardous earthworks and natural slopes.

Study on the Mechanical Behaviour of Flexible Barriers by in situ Testing and Modelling

This study presents the results of a real scale in situ experimental test conducted in order to analyse the dynamics of the impact of a debris flow on flexible barriers. The analyses of the tests, together with the calculation of the thrust caused by the flow have been conducted with both numerical 3D analysis performed with a FEM model and with the application of a simplified analytical model developed by the authors. A Finite Element Method (FEM) model was set up in order to analyze the stress strain behaviour of the netting. The comparison between experimental and numerical results have made it possible to analyse the dynamics of the impact and to better understand the complex resisting mechanism of flexible barriers.

The Boschetto landslide: monitoring, numerical analysisand interpretation

This short paper illustrates the studies carried out on a landslide phenomenon occurred during the Spring of 2013 in the Parma Appenines. The activation/reactivation of the landslide caused the interruption of a provincial road and the disruption of few houses. No fatalities occurred. The work presented is aimed to reconstruct the process that caused the landslide activation, describes the monitoring facilities that were set up after the landslide activation and how their data can be used to develop an appropriate numerical model.