Добірка наукової літератури з теми "Metodo rockfall risk assessment"

Abstract. This paper contains a method for the analysis of rockfall risk along roads and motorways. The method is derived from the Rockfall Hazard Rating System (RHRS) developed by Pierson et al. (1990) at the Oregon State Highway Division. The RHRS provides a rational way to make informed decisions on where and how to spend construction funds. Exponential scoring functions are used to represent the increases, respectively, in hazard and in vulnerability that are reflected in the nine categories forming the classification. The resulting total score contains the essential elements regarding the evaluation of the degree of the exposition to the risk along roads. In the modified method, the ratings for the categories "ditch effectiveness", "geologic characteristic", "volume of rockfall/block size", "climate and water circulation" and "rockfall history" have been rendered more easy and objective. The main modifications regard the introduction of Slope Mass Rating by Romana (1985, 1988, 1991) improving the estimate of the geologic characteristics, of the volume of the potentially unstable blocks and the underground water circulation. Other modifications regard the scoring for the categories "decision sight distance" and "road geometry". For these categories, the Italian National Council's standards (Consiglio Nazionale delle Ricerche - CNR) have been used (CNR, 1980). The method must be applied in both the traffic directions because the percentage of reduction in the decision sight distance greatly affects the results. An application of the modified method to a 2km long section of the Sorrentine road (no 145) in Southern Italy was developed. A high traffic intensity affects the entire section of the road and rockfalls periodically cause casualties, as well as a large amount of damage and traffic interruptions. The method was applied to seven cross sections of slopes adjacent to the Sorrentine road. For these slopes, the analysis shows that the risk is unacceptable and it should be reduced using urgent remedial works.

This paper presents and compares the main methods of hazard and risk assessment for road slopes. Hazard assessment is achieved by rating several parameters such as the slope’s geometry, traffic conditions, the geology and the rockmass properties, weather conditions, historical rockfall data etc. A hazard assessment can also be executed using 2D or 3D trajectory models, by combining the frequency of a rockfall and the kinetic energy of a falling rock. Several methodologies have been developed for risk assessment, varying from simplistic approaches to comprehensive probabilistic or quantitative risk assessment methods. Finally, the most suitable methods were used in order to assess the level of hazard and risk as an example (the data from two sections of the national road at Tempi Gorge, Greece) where many rockfall events occurred in the past few years.

Quantitative rockfall hazard and specific risk assessment of the selected municipalities within the České Švýcarsko National Park was performed using two rockfall hazard analysis modelling codes. CONEFALL and RockFall Analyst codes were used to delimit rockfall hazard regions. Specific risk to buildings was consequently assessed using results from the hazard analysis and literature-derived vulnerability values. Results of hazard and risk assessments for two nearby municipalities were compared and evaluated. Both models provide similar rockfall hazard values in areas characterized with relatively steep (36°–50°), convex and short slopes (up to 200 m). Whereas in regions with less steep (20°–35°), concave and longer slopes (about 350 m) the predicted rockfall hazard differs considerably. We argue that the results of the RockFall Analyst are more reliable due to complex input data and modelling approach which closely resembles the natural process of falling rocks on forested slopes. Differences in hazard assessment are further reflected in assigning risk values to exposed buildings, where CONEFALL is more conservative.

Abstract. Rockfall risk analysis for mitigation action design requires evaluating the probability of rockfall events, the spatial probability and intensity of impacts on structures, their vulnerability, and the related expected costs for different scenarios. These tasks were integrated in a quantitative risk assessment procedure supported by 3D rockfall numerical modelling performed by the original code HY-STONE. The case study of Fiumelatte (Varenna, Italy), where a large rockfall in November 2004 resulted in 2 casualties, destruction of several buildings and damage to transportation corridors, is discussed. The numerical model was calibrated by a back analysis of the 2004 event, and then run for the whole area at risk by considering scenarios without protection (S0), with a provisional embankment (S1), and with a series of long-term protection embankments (S2). Computed impact energy and observed damage for each building impacted in 2004 were combined to establish an empirical vulnerability function, according to which the expected degree of loss for each element at risk was computed. Finally, costs and benefits associated to different protection scenarios were estimated, in order to assess both the technical performance and the cost efficiency of different mitigation options.

Rockfall hazard is assessed using Rockfor.net, which is one dimensional tool for assessing the protective function of forests against rockfall. Three sites where chosen to test the tool with different morphological and forest conditions. For each site, it was evaluated how the boulder size and forest composition affects the probability of the rocks to surpass the forested slope. The Rockfor.net was also used for back calculations of past event, which happened during the floods in July 1997 in the village of Bystřička in the Vsetínské vrchy Hills. In this case, also a partial quantitative risk assessment with suggestions for risk management was performed.

Rockfalls represent significant risks to safe and efficient use of transportation corridors. In this paper, we address the management of rockfall risk through baseline remote monitoring of susceptible slopes (every 2–4 months) along a transportation corridor along the Fraser River valley in western Canada using a terrestrial laser scanner and supporting remote sensing technologies. This includes identifying potential rockfall source zones based on incipient signs of failure, tracking kinematics in three dimensions to better understand the mechanism of failure, estimating potential failure volumes based on bounding joint structure, and transmitting this information to the railway operator for an assessment of risk. We demonstrate our approach for one case along the line where we identified several potential failures ranging in volume from 48 to 4200 m3. Our projections of the location of failures were successful, in that volume projections were within 10%–55%, and the anticipated kinematics and failure mechanism were consistent with the assessment of post-failure rockfall scar geometries. Accurate volume and kinematics estimates are important for the assessment of hazard and risk as well as the planning of risk mitigation options. In general, this approach can be used to better manage risk from rockfall hazard in communities, transportation corridors, or other infrastructure.

The Rockfall Management System developed for Tennessee DOT (TennRMS)integrates a customized rockfall risk rating system, web-based GIS application, and rockfall database to provide a robust single interface for interacting with rock slope information. The system should prove to be a valuable tool for the proactive management of rock slopes. The most important use of the system will be to identify and prioritizing rock slopes with the greatest potential for rockfall in order to provide decision makers with all the necessary information they need to plan remediation efforts. Over time, TennRMS can be used to track costs and effectiveness of different remediation methods used on problem rock slopes. Three papers have been developed for publication in peer reviewed journals. The papers describe the work done in support of developing Tennessee's Rockfall Management System (TennRMS) and its components. The system can be described by its conceptual framework and actual implemented components. Asset management incorporating risk & decision analysis and knowledge management makes up the conceptual framework. The system components include a field data collection system using PDA's, a rockfall database and a web-based GIS interface. The papers articulate the development and implementation of the various components and to provide a detailed review of rockfall management systems as implemented over the past 15 years.
Ph. D.

L’aléa chute de blocs est caractérisé par le détachement brutal d’une masse rocheuse, depuis une paroi (sub)verticale, qui se propage rapidement vers l’aval par rebonds successifs. Ces événements, fréquents en zones de montagne, représentent un aléa majeur pour les infrastructures collectives et les habitations, et induisent fréquemment de graves accidents. En France, par exemple, le détachement d’un volume rocheux de 30 m3 en 2014 a provoqué le déraillement du train touristique des Pignes, faisant deux victimes et neuf blessés. En 2015, l’endommagement des voies et la perturbation du trafic ferroviaire suite à un événement rocheux survenu entre Moûtiers et Bourg-Saint-Maurice a induit 1.34M€ de réparations, et 5.4M€ de dommages indirects.Ces différents événements illustrent bien notre vulnérabilité face aux événements rocheux, et soulignent que les collectivités locales et les pouvoirs publics sont encore fréquemment démunis en matière de méthode de diagnostic et d’analyse du risque de chute de blocs. Dans ce contexte, l’évaluation des risques par une approche de type quantitative, appelée QRA (Quantitative Risk Assessment), est devenue incontournable pour l’aménagement des territoires de montagne et le choix des mesures de mitigation. Chaque terme de l’équation du risque, dont les composantes principales sont l’aléa, la vulnérabilité, et l’exposition, sont alors fidèlement quantifiés, offrant des informations sur les dommages potentiels.Malgré le vif intérêt alloué aux approches de type QRA pour la gestion des risques rocheux, de telles applications restent encore inhabituelles. La rareté de ces approches est principalement liée à la difficulté à évaluer précisément chacune des composantes du risque. De plus, les quelques études qui proposent une approche QRA dans le domaine rocheux font généralement l’hypothèse de la stationnarité du processus, alors que l’étalement urbain, ou l’évolution de l’occupation des sols, qui modifient le fonctionnement du processus ne sont pas intégrés. Enfin, le risque rocheux – comme la plupart des autres risques naturels – est exprimé par la moyenne des dommages. Cependant, cette moyenne arithmétique est associée à plusieurs faiblesses, et n’offre qu’une seule valeur du risque, généralement inadaptée aux différentes contraintes auxquelles doivent faire face les gestionnaires. Dans ce contexte, l’objectif de cette thèse est de renforcer les bases formelles du calcul du risque dans le domaine des chutes de blocs, d’évaluer les effets des changements environnementaux sur le risque rocheux, et de proposer une méthode où le risque de chutes de blocs est quantifié à partir de mesures de risque alternatives à la moyenne arithmétique. A cet effet, nous proposons une procédure holistique de QRA où le risque rocheux est quantifié en combinant un modèle de simulation trajectographique avec des courbes de vulnérabilité et un large spectre de volume rocheux et de zones de départ de chutes de blocs. La faisabilité et l’intérêt de cette procédure est illustré sur deux cas d’études réels : la commune de Crolles (Alpes Françaises), et la vallée de l’Uspallata (Cordillère des Andes). Par ailleurs, nous mesurons l’effet des changements environnementaux sur le risque de chutes de blocs en appliquant la QRA dans différents contextes d’utilisation et d’occupation des sols. Enfin, nous proposons une approche innovante où deux mesures de risque, dites "quantile-based measures", sont introduites. Ces dernières permettent une meilleure prise en compte des événements extrêmes et permettent d’envisager la gestion du risque à divers horizons temporels
Rockfalls are a common type of fast moving landslide, corresponding to the detachment of individual rocks and boulders of different sizes from a vertical or sub-vertical cliff, and to their travel down the slope by free falling, bouncing and/or rolling. Every year, in the Alpine environment, rockfalls reach urbanized areas causing damage to structures and injuring people. Precise rockfall risk analysis has therefore become an essential tool for authorities and stakeholders in land-use planning.To this aim, quantitative risk assessment (QRA) procedures originally developed for landslides have been adapted to rockfall processes. In QRAs, rockfall risk for exposed elements is estimated by coupling the hazard, exposure and vulnerability components. However in practice, the estimation of the different components of risk is challenging, and methods for quantifying risk in rockfall-prone regions remain scarce. Similarly, the few studies which so far performed QRAs for rockfall assume stationary, precluding reliable anticipation of the risk in a context where environmental and societal conditions are evolving rapidly and substantially. Moreover, rockfall risk remains - as for most of natural hazards - always defined as the loss expectation. This metric offers a unique risk value, usually inconsistent with short/long term constraints or trade-offs faced by decision-makers.On this basis, this PhD thesis therefore aims at (i) reinforcing the basis of QRA, (ii) assessing the effect of environmental changes on rockfall risk, and (iii) proposing method for quantifying rockfall risk from measures of risk alternative to the standard loss expectation. In that respect, we propose a QRA procedure where the rockfall risk is quantified by combining a rockfall simulation model with the physical vulnerability of potentially affected structures and a wide spectrum of rockfall volumes as well as release areas. The practicability and interest of this procedure is illustrated on two real case studies, i.e. the municipality of Crolles, in the French Alps, and the Uspallata valley, in the central Andes mountains. Similarly, the effect of environmental changes on rockfall risk is considered by comparing rockfall risk values in different land-use and land-cover contexts. Last, we implement in our procedure on an individual basis two quantile-based measures, namely the value-at-risk and the expected-shortfall, so as to assess rockfall risk for different risk-management horizon periods. All in all, this PhD thesis clearly demonstrates the added value of QRA procedure in the field of rockfall, and reinforces its basis by implementing analytical, statistical or numerical models. The resulting panel of risk maps, also proposed under non-stationary contexts, are of major interest for stakeholders in charge of risk management, and constitute appropriate basis for land-use planning and prioritizing of mitigation strategies

Rock slope instabilities represent a major hazard for human activities, often causing economic losses, property damages and maintenance costs, as well as injuries or fatalities. Rock slope stability is so one of the most important issue in mountain areas and mines. Although, in fact, rock falls along highways and railways in mountainous terrains do not pose the same level of economic risk as large-scale failures (which can cause the closure of major transportation routes for several days), the number of people killed by rockfalls tends to be of the same order as people killed by all other instabilities affecting rock slopes. An accurate characterisation of the rock mass discontinuities allows to understand the most probable failure mechanism and individuate the source area, since the local orientation of the mesh of the 3D model of the slope. A proper geostructural survey, together with a high definition 3D model of the slope, allows, in fact, to evaluate the position of source area; the geostructural survey permits also the modelling of the volume distribution of the removable blocks. The position of the source area, the position of the blocks and the high definition 3D model of the slope are fundamental parameters for the modelling of the run out of the blocks, defining so the trajectory of the blocks and the associated kinetic energy for the design of the most appropriate protection works. The estimate of the blocks volume can be conducted by means of codes that use the structural features of the rock surface to identify the boundaries of the polygons that represent the blocks. An accurate geomechanical characterisation is therefore crucial to gather information about the most probable failure mechanism, the position of source area and the volume of removable blocks. Semiautomatic methods in addition to manual methods for discontinuities extraction, have allowed to reduce the user-dependant subjectivity and the consume of time over the last few decades, to obtain details of the rock mass structures. The thesis shows the application of different tools for the structural characterisation and the stability assessment on a number of different walls affected by rockfall in open pit mines in Australia. 3D models of walls have been built since close range photogrammetric surveys using Siro3D code (Datamine SiroVision). SiroJoint (in built in the Siro3D package) has been used to manually detect the discontinuities, while DiAna, Facets plug-in of CloudCompare and I-site Studio (Maptek) codes have been used for the semiautomatic discontinuities extraction. Stereoplots of the discontinuities extracted by manual and semiautomatic methods have been so compared and kinematic indices for plane failure, wedge failure, block toppling, and flexural toppling have been calculated. The structural survey has been then used to perform the distribution of the block volume thanks to a multi-function discrete fracture network (DFN) generator and to describe removability and stability of the blocks using the Block Theory (Goodman & Shi) and the Factor of Safety (Hoek & Bray). This stability analysis has been carried out with SiroModel software (developed by CSIRO within Large Open Pit-LOP project). 3D kinematic analysis has been then performed using DiAna-K code, since the semiautomatic geostructural survey carried out with DiAna and the high definition 3D model of the slope. DiAna and DiAna-K codes has been developed within the Department of earth Sciences of the University of Florence. The integration of the 3D kinematic analysis with the stability analysis of the blocks extracted with a DFN allows to objectively quantify since remote survey data the main geometric input parameters necessary for a complete and reliable rockfall hazard analysis, such as slope high resolution morphology, source areas and volume of unstable blocks, thanks to which is possible to calculate the kinetic energy along the run out. The study is aimed to: i) evaluate how artificial cuts affect the reliability of semiautomatic discontinuities extraction methods in comparison to manual discontinuities extraction methods; ii) compare stereoplots of semiautomatic and manual discontinuities extraction in case of artificial cuts; iii) integrate 3D kinematic analysis with the stability analysis of the blocks extracted with a multi-function discrete fracture network generator. The comparison of the stereoplots of the discontinuity planes produced with SiroJoint and DiAna shows results somehow comparable; moreover, this application revealed a number of interesting advantages and drawbacks of manual and semiautomatic methods, which can be useful to overcome some current limitations and improve the quality of the remote geostructural survey and then of the rockfall simulations. --------------------------------------------------------------------------------------------------------------------------------------------------------------------------- La stabilità di versanti in roccia costituisce un tipo di frana che presenta un rischio elevato. Tale rischio è elevato in considerazione della probabilità che si abbiano vittime o feriti, dei tempi di interruzione dell’infrastruttura danneggiata e dei costi della sua messa in esercizio, oltre che di installazione dei più idonei sistemi di protezione. La caduta massi è infatti uno dei rischi maggiori in aree montane, così come anche in aree minerarie. Malgrado infatti i volumi di versate mobilizzati dai crolli siano in genere minori rispetto ai volumi dei corpi di frana di altri fenomeni di versante, l’elevata velocità del fenomeno fa sì che il numero di vittime avute a causa di caduta massi sia dello stesso ordine di altri fenomeni di versante. Un’attenta caratterizzazione delle discontinuità presenti all’interno dell’ammasso roccioso consente comprendere quali meccanismi cinematici siano più probabili ed individuare le possibili aree fonte dei distacchi. Pertanto, un corretto rilievo geostrutturale, insieme ad un modello 3D ad alta definizione del pendio, costituisce un dato di input essenziale per la corretta modellazione del run out dei massi in termini di percorsi e di energie cinetiche in gioco, permettendo quindi la progettazione delle contromisure di protezione più appropriate. Sono pertanto essenziali alcuni dati per la corretta modellazione 3D della rockfall analysis: un modello del terreno 3D di alta definizione (ricavato con rilievo fotogrammetrico o laser scanning), la posizione delle aree di distacco dei blocchi ed il volume dei blocchi instabili. Un accurato rilievo geostrutturale è alla base dell’individuazione dei meccanismi e quindi delle aree la cui esposizione risulta più favorevole all’innesco di caduta massi: un accurato rilievo geostrutturale è quindi alla base di una corretta valutazione del rischio caduta massi. Negli ultimi decenni ai metodi di rilevamento manuale delle discontinuità si sono aggiunti i metodi semiautomatici di estrazione delle discontinuità, che consentono di individuare le discontinuità a partire da parametri geometrici settati dall’operatore, riducendo molto la soggettività del rilievo ed il tempo necessario. Il rilievo geostrutturale consente quindi di calcolare gli indici di pericolosità cinematica e di avere la distribuzione del volume dei blocchi rimovibili. Gli indici di pericolosità cinematica consentono di attribuire un valore a ciascuno dei cinematismi posibili (scivolamento planare, civolamento di cunei, ribaltamento di blocchi, ribaltamento di flessure) in funzione dell’orientazione del versante; se si dispone di una mesh sarà quindi possibile capire quali porzioni siano più esposte al distacco di blocchi, in ragione della loro esposizione. Il rilievo geostrutturale consente inoltre di ricavare la distribuzione del volume dei blocchi mediante l’utilizzo di codici di calcolo che costruiscono una rete discreta di discontinuità all’interno dell’ammasso roccioso, mediante una modellazione di tipo stocastico. La tesi analizza e confronta l’applicazione di diversi codici per la caratterizzazione geostrutturale e per la successiva valutazione della stabilità di versante, su vari versanti in roccia situati in miniere di tipo open-pit in Australia. I modelli 3D dei versanti in roccia sono stati ricavati tramite fotogrammetria con il software Siro3D (Datamine SiroVision). Il codice SiroJoint (Siro3D package) è stato utilizzato per il rilievo manuale delle discontinuità, mentre per il rilievo semiautomatico delle discontinuità sono stati utilizzati i codici DiAna, Facets (CloudCompare) e I-Site Studio (Maptek). Sono stati quindi ricavati e gli stereoplots delle discontinuità estratte con metodi manuali e automatici e sono stati calcolati e confrontati gli indici di pericolosità cinematica per ciascun cinematismo. Il rilievo strutturale effettuato è stato utilizzato per ricavare tramite un generatore multifunzione di un sistema di fratture continue (discrete fracture network, DFN) all’interno del software SiroModel (sviluppato da CSIRO all’interno del progetto LRGE Open Pit mines – OPS), che ha consentito a partire dalla Teoria di Goodman e Shi sulla rimovibilità dei blocchi e dal calcolo del Fattore di Sicurezza (Factor of Safety; Hoek & Bray, 1981) di comprendere la distribuzione del volume dei blocchi instabili, stabili grazie all’attrito e stabili (Type I, II e III della classificazione dei blocchi di Goodman & Shi). I blocchi sono stati estratti mediante una modellazione stocastica a partire dall’orientazione e dalla persistenza delle discontinuità. L’analisi cinematica 3D è stata condotta tramite DiAna-K, usando come dati di il rilievo semiautomatico delle discontinuità ed il modello 3D del terreno ottenuto con tecnica fotogrammetrica. I codici DiAna e DiAna-K sono stati sviluppati dal Dipartimento di Scienze della Terra dell’Università di Firenze. L'integrazione dell’analisi cinematica 3D e dell’analisi di stabilità finalizzata alla definizione del volume dei blocchi rimovibili permette una definizione quantitativa ed oggettiva dei principali dati geometrici necessari per la modellazione del rischio di caduta massi, consentendo quindi di definire le traiettorie, la velocità e l’energia cinetica dei blocchi per una corretta progettazione degli interventi di mitigazione del rischio. Lo studio è stato finalizzato a: i) Valutare come la presenza di tagli artificiali influenzi l’applicabilità di metodi semiautomatici per l’estrazione delle discontinuità, rispetto a metodi manuali; ii) Confrontare gli stereoplot e gli indici di pericolosità cinematica dei rilievi geostrutturali effettuati con metodi manuali o con metodi semiautomatici di estrazione delle discontinuità; iii) Integrare l’analisi cinematica 3D con l’analisi di stabilità dei blocchi estratti grazie a DFN.

Abstract Pipeline geohazard assessment involves the delineation and quantification of threat severity associated with a suite of geohazard mechanisms deemed credible for a specific setting or project. The context for a typical assessment is loss of containment from the pipeline — an ultimate limit state (ULS) — considering individual geohazard mechanisms (e.g., landslide, fault displacement, rockfall, subsidence, etc.). To estimate the probability of loss of containment associated with a particular geohazard mechanism at a given location, the evaluation process can be partitioned into an estimate of the probability of occurrence of the geohazard mechanism at that location, and the conditional probability of loss of pipe integrity should the event occur. The product of these two probabilities is termed “susceptibility” expressed as loss of containment events per year at a given location. A typical approach to manage geohazards assessed in this way is to set a target susceptibility threshold to determine mitigation requirements to reduce the estimated susceptibility value for individual geohazards. The rationale for selecting a target susceptibility threshold value has been a topic of interest in recent pipeline projects in Canada. This paper demonstrates a reliability-based approach in rationalizing the selected pipeline geohazard target susceptibility threshold and linking geohazard assessment results to Quantitative Risk Assessment (QRA) of all threat categories in ASME B31-8S.