Gessica Umili

A new method for automatic discontinuity traces sampling on rock mass 3D model

A new automatic method for discontinuity traces mapping and sampling on a rock mass digital model is described in this work. The implemented procedure allows one to automatically identify discontinuity traces on a Digital Surface Model: traces are detected directly as surface breaklines, by means of maximum and minimum principal curvature values of the vertices that constitute the model surface. Color influence and user errors, that usually characterize the trace mapping on images, are eliminated. Also trace sampling procedures based on circular windows and circular scanlines have been implemented: they are used to infer trace data and to calculate values of mean trace length, expected discontinuity diameter and intensity of rock discontinuities. The method is tested on a case study: results obtained applying the automatic procedure on the DSM of a rock face are compared to those obtained performing a manual sampling on the orthophotograph of the same rock face.

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.

A tool for semi-automatic linear feature detection based on DTM

Abstract The tectonic movement along faults is often reflected by geomorphological features such as linear valleys, ridgelines and slope-breaks, steep slopes of uniform aspect, regional anisotropy and tilt of terrain. In the last years, remote sensing data have been used as a source of information for the detection of tectonic structures. In this paper, a new fully 3D approach for semi-automatic extraction and characterization of geological lineaments is presented: linear features are detected on a DTM by means of algorithms based on principal curvature values, and then they are grouped according to data collected from literature review regarding expected orientation of lineaments in the studied area. The overall positive aspects of this semi-automatic process were found to be the informativeness on geological structure for preliminary geological assessment and set identification, the possibility to identify the most interesting portions to be investigated and to analyze zones that are not directly accessible. This method has been applied to a geologically well-known area (the Monferrato geological domain) in order to validate the results of the software processing with remotely sensed data collected from literature review. As regard to orientation, spatial distribution and length of the lineaments, the study demonstrates a correspondence of the obtained results with both remote sensed linear features and field geostructural data.

Some Open Issues on Rockfall Hazard Analysis in Fractured Rock Mass: Problems and Prospects

Risk is part of every sector of engineering design. It is a consequence of the uncertainties connected with the cognitive boundaries and with the natural variability of the relevant variables. In soil and rock engineering, in particular, uncertainties are linked to geometrical and mechanical aspects and the model used for the problem schematization. While the uncertainties due to the cognitive gaps could be filled by improving the quality of numerical codes and measuring instruments, nothing can be done to remove the randomness of natural variables, except defining their variability with stochastic approaches. Probabilistic analyses represent a useful tool to run parametric analyses and to identify the more significant aspects of a given phenomenon: They can be used for a rational quantification and mitigation of risk. The connection between the cognitive level and the probability of failure is at the base of the determination of hazard, which is often quantified through the assignment of safety factors. But these factors suffer from conceptual limits, which can be only overcome by adopting mathematical techniques with sound bases, not so used up to now (Einstein et al. in rock mechanics in civil and environmental engineering, CRC Press, London, 3–13, 2010; Brown in J Rock Mech Geotech Eng 4(3):193–204, 2012). The present paper describes the problems and the more reliable techniques used to quantify the uncertainties that characterize the large number of parameters that are involved in rock slope hazard assessment through a real case specifically related to rockfall. Limits of the existing approaches and future developments of the research are also provided.

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.

A Tool for Semi-automatic Geostructural Survey Based on DTM

Tectonic movement along faults is often reflected by characteristic geomorphological features such as linear valleys, ridgelines and slope-breaks, steep slopes of uniform aspect, regional anisotropy and tilt of terrain. In the last years, the remote sensing data has been used as a source of information for the detection of tectonic structures. In this paper, we present a new approach for semi-automatic extraction and characterization of geological lineaments. The overall positive aspects of this semi-automatic process were found to be the rapidity of preliminary assessment, the possibility to identify the most interesting portions to be investigated and to analyze zones that are not directly accessible. This method has been applied to a geologically well-known area (the Monferrato geological domain) in order to validate the results of the software processing with literature data. Results obtained are discussed and preliminary remarks are put forward.

An Integrated Approach for Monitoring Slow Deformations Preceding Dynamic Failure in Rock Slopes: A Preliminary Study

Rock slope monitoring is a major aim in territorial risk assessment and mitigation. The high velocity that usually characterizes the failure phase of rock instabilities makes the traditional instruments based on slope deformation measurements not applicable for early warning systems. On the other hand the use of acoustic emission records has been often a good tool in underground mining for slope monitoring. In this paper the design and installation of a monitoring system based on acoustic emission aimed at interpret and forecast a large rock instability phenomenon is reported together with some preliminary geophysical and geomechanical studies performed.

A Simplified Analytical Model for the Design of Flexible Barriers Against Debris Flows

A debris flow is usually represented by a mixture of solid particles of various sizes and water, flowing along a laterally confined inclined channel-shaped region; debris flow protection barriers are the focus of this research. In particular the paper presents a simplified structural model of cable-like retention barriers based upon the equation of equilibrium of wires under large displacements condition. Inputting the debris flow features, the model returns restraining forces and cable stresses that can then be used for an appropriate barrier design. Some parametrical tests were performed to analyze how the impact velocity and the mass density of the debris influence the maximum tensile force and the acting load in the cables: also the energy associated with debris flow is assessed. Results are here presented and discussed.