Dissertations / Theses on the topic 'Rockfal hazard'

Climate change has widespread impacts on human and natural systems worldwide. The pronounced air temperature warming detected worldwide could explain unusual events, as for example the increment of extreme precipitation events, increased incidence of summer heatwaves and slope instability. The possible presence of non-climatic forcings affecting temperature records, as for example land-use and land-cover changes, could introduce significant bias in the records and uncertainty on global overall temperature trends. This could somehow alterate, on the one hand, the perception of global warming, and on the other hand, all temperature-related analyses and models. Nevertheless, a robust assessment of climate warming patterns entails not only the analysis of all climate variables involved, but also the full understanding of the impacts on the natural systems, as for example the cryosphere, that could be used as terrestrial indicators of climate change. Chapter 1 shed light on the main scientific question investigated in the thesis, presenting the proposed investigation strategy, and the techniques applied. After an introduction on the issue of increasing air temperature vaiability in the current context of climate change, the two macrotopics of the thesis are presented and briefly outlined (Chapter 2 and 3). In Chapter 2, we investigate the nexus between temperature variations and urbanization trends, by analysing data recorded from weather instruments worldwide. After an extended introduction on the Urban Heat Island effect and its implications for climate warming trends at regional and global scale, we propose several methods to investigate the presence of a possible relation between air temperature variations and urbanizations dynamics with time, based on nightlights satellite measurements as proxy of urbanization. We applied a global scale analysis on more than 5000 temperature stations from the Berkeley Earth dataset in the period 1992-2013. Results highlight the tendency of urbanization to affect temperature trend at continental and regional scales. Significant positive concordant trends in temperature and nightlights variations have been detected, especially in developing and emerging regions, where the effects of growing urbanization are more evident. In Chapter 3 we turn to investigate the effects of air temperature variations on the hydrogeological hazard risk in those environments that are among the most sensitive to climate change, i.e. the high elevation sites. In alpine areas, and in particular in high mountain areas, the potential effects of environmental changes on air temperature data are minimum, since these areas are only slightly affected by urbanization dynamics and land-use changes. More in detail, in Chapter 3, we propose a statistical-based tool for the detection of the role of temperature, in association with other climate-related variables (as precipitation), in the triggering of slope stability. This approach is aimed to point out the potential climatic triggering climate factors for the slope failure. It has thought up as a tool for a better comprehension of the possible effects of air temperature variations on environmental dynamics, also in the presence of sparse and poor-quality data. We performed this method on a catalogue of 41 rockfalls in the Italian Alps, focusing on the role of temperature on slope instability preparation and initiation, and on cryosphere-related dynamics. The final purpose is detecting a possible linkage between slope failures and meteorological anomalies, and results suggest a major role of temperature as a preparatory/triggering factor. Rockfalls occurred in association with significant temperature anomalies in 83% of our case studies, and different regional patterns emerge from the data. Based on these results, temperature can be considered as a key factor contributing to slope failure occurrence in different ways, in presence of both warm and cool temperature anomalies. Chapter 4 presents a critical analysis in terms of how much it could be really answered of the main scientific questions with this work, what are the limitations encountered, which questions remain open and the possible further developments.

Rockfall from rock slopes adjacent to roadways is a major hazard and poses a problem for transportation agencies across the country. The state of Tennessee has implemented the Tennessee Rockfall Management System (RMS) as a means of reducing the liabilities associated with rockfall hazard. It utilizes digital data acquisition via PDAs coupled with distribution via an expandable web-based GIS database. The Tennessee Rockfall Hazard Rating System (RHRS) is part of the Tennessee RMS and assigns a numeric hazard rating according relative hazard for all slopes identified as having a high potential for delivering rock blocks onto Tennessee Department of Transportation maintained roadways. The Tennessee RHRS uses standard rock slope failure mechanisms (planar failure, wedge failure, topple failure, differential weathering, and raveling) along with the site and roadway geometry to assess the rockfall hazard of an individual slope. This study suggests methods that will expedite fieldwork, including an informational guide on how to properly identify individual failure mechanisms in the field. Also, the study examines the current method of scoring abundance and suggests an alternative, multiplicative approach. The alternative of using a multiplicative abundance is considered and its results summarized.
Master of Science

Computer simulation of rockfalls has been widely used in rockfall analysis in recent years, and the coefficient of restitution is an important parameter input that is difficult to determine. Aimed at finding an easy solution to this problem, three stages of laboratory and field tests have been carried out. Rockfall trajectory analysis at a specific site has been done as an application to verify the method developed. In the first stage of laboratory testing, quasi-spherical rock "'balls" made from different rock samples were dropped from 1 m onto polished rock slabs that were clamped on a concrete deck, which can be set to different slope angles. A high-speed video camera was used to record the impact processes, and normal and tangential coefficients of restitution were calculated from the video records. The results show a linear relationship between the normal restitution coefficient and the Schmidt hammer numbers of both the rock slabs and the falling rock "balls", and the slope angle. An empirical equation was then established to calculate the normal coefficient of restitution from those three parameters. However, the correlations between the tangential coefficient of restitution and the above parameters are poor, indicating that the tangential coefficient of restitution is not adequately determined by such rock properties. The second stage of laboratory testing was under more practical conditions. Three different rough rock blocks were used as rock slopes. Angular rock boulders were dropped from different heights onto the rock blocks, and a rock "ball" was also used to make a comparison. The results show that the normal coefficients of restitution from impacts of angular rocks are much smaller than those of rock "'balls", and have a linear correlation with those calculated from the empirical equation obtained by the earlier test. Tests on beds of gravel, soil, rock fragments and sand have also been carried out to obtain the coefficients of restitution of those materials. Finally, field tests have been carried out at a quarry site in Lyttelton Basalt rock boulders of about 0.3 m in diameter were dropped from about 4 m onto rock and debris slopes using an excavator. The values of restitution coefficients obtained are similar to those from laboratory tests but larger than those calculated from the empirical equations due to the effect of weathering and surface roughness of rocks in the field on the Schmidt hammer measurement. Forty basalt boulders were then rolled down a bench slope of about 16 m, three cameras were used to record the rockfall processes. Two different rockfall simulation programs (CRSP and RocFall) were used to simulate the rockfall processes. The simulated bounce heights and velocities from CRSP are close the field trial, while those from RocFall are smaller than the field results. Comprehensive rockfall analysis has been carried out for the Marine apartments, Sumner, where a steep cliff of 35-45 m represents potential rockfall hazards to a car park and proposed buildings at the base. Site investigation, rockfall simulation and risk assessment have been carried out for the site. The results show that without any protection measures, a majority of rocks from the cliff face reach the edge of the car park. The probability of an accident at the car park is moderate (1 in 195 years), while the probability of fatality at the car park is low (8.69* 10-6) and acceptable under the proposed risk criteria for "Major Civil Engineering Projects".

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.

Thesis (Ph.D.)--Tel Aviv University, Department of Geophysics and Planetary Sciences,
This work was submitted as M.Sc. Thesis to the Department of Geophysics and Planetary Sciences, Tel Aviv University / T.P. "September 2008" At head of title: Tel-Aviv University. Raymond and Beverly Sackler faculty of exact sciences. Includes bibliographical references.

The Canterbury Earthquake Sequence (CES) of 2010-2011 produced large seismic moments up to Mw 7.1. These large, near-to-surface (<15 km) ruptures triggered >6,000 rockfall boulders on the Port Hills of Christchurch, many of which impacted houses and affected the livelihoods of people within the impacted area. From these disastrous and unpredicted natural events a need arose to be able to assess the areas affected by rockfall events in the future, where it is known that a rockfall is possible from a specific source outcrop but the potential boulder runout and dynamics are not understood. The distribution of rockfall deposits is largely constrained by the physical properties and processes of the boulder and its motion such as block density, shape and size, block velocity, bounce height, impact and rebound angle, as well as the properties of the substrate. Numerical rockfall models go some way to accounting for all the complex factors in an algorithm, commonly parameterised in a user interface where site-specific effects can be calibrated. Calibration of these algorithms requires thorough field checks and often experimental practises. The purpose of this project, which began immediately following the most destructive rupture of the CES (February 22, 2011), is to collate data to characterise boulder falls, and to use this information, supplemented by a set of anthropogenic boulder fall data, to perform an in-depth calibration of the three-dimensional numerical rockfall model RAMMS::Rockfall. The thesis covers the following topics: • Use of field data to calibrate RAMMS. Boulder impact trails in the loess-colluvium soils at Rapaki Bay have been used to estimate ranges of boulder velocities and bounce heights. RAMMS results replicate field data closely; it is concluded that the model is appropriate for analysing the earthquake-triggered boulder trails at Rapaki Bay, and that it can be usefully applied to rockfall trajectory and hazard assessment at this and similar sites elsewhere. • Detailed analysis of dynamic rockfall processes, interpreted from recorded boulder rolling experiments, and compared to RAMMS simulated results at the same site. Recorded rotational and translational velocities of a particular boulder show that the boulder behaves logically and dynamically on impact with different substrate types. Simulations show that seasonal changes in soil moisture alter rockfall dynamics and runout predictions within RAMMS, and adjustments are made to the calibration to reflect this; suggesting that in hazard analysis a rockfall model should be calibrated to dry rather than wet soil conditions to anticipate the most serious outcome. • Verifying the model calibration for a separate site on the Port Hills. The results of the RAMMS simulations show the effectiveness of calibration against a real data set, as well as the effectiveness of vegetation as a rockfall barrier/retardant. The results of simulations are compared using hazard maps, where the maximum runouts match well the mapped CES fallen boulder maximum runouts. The results of the simulations in terms of frequency distribution of deposit locations on the slope are also compared with those of the CES data, using the shadow angle tool to apportion slope zones. These results also replicate real field data well. Results show that a maximum runout envelope can be mapped, as well as frequency distribution of deposited boulders for hazard (and thus risk) analysis purposes. The accuracy of the rockfall runout envelope and frequency distribution can be improved by comprehensive vegetation and substrate mapping. The topics above define the scope of the project, limiting the focus to rockfall processes on the Port Hills, and implications for model calibration for the wider scientific community. The results provide a useful rockfall analysis methodology with a defensible and replicable calibration process, that has the potential to be applied to other lithologies and substrates. Its applications include a method of analysis for the selection and positioning of rockfall countermeasure design; site safety assessment for scaling and demolition works; and risk analysis and land planning for future construction in Christchurch.

Due to the exponential grown of the population within the last decades, the landslide hazard assessment of earthflows and rockfalls and their hazard mapping have become an essential tool for the territory management, mostly in mountainous areas. The landslide hazard was defined as the probability of occurrence of a potentially damaging phenomenon in a certain area and within a given period of time. Thus, the probability of occurrence (or frequency) for each type of landslide and magnitude must be known. The aim of this research is to develop an objective, quantitative and reproducible methodology to obtain the magnitude-frequency relations for medium and large size earthflows and rockfalls. This procedure has been set up in the Barcedana Valley and Montsec Range for large earthflows and rockfalls, respectively. Both study areas are located within the Tremp Basin (Eastern Pyrenees). Concerning the earthflows, they have been split between 1) reactivations and 2) intact slopes. The frequency of the reactivations has been obtained by analysing 11 sets of orthophotos covering a period from 1956 to 2013. The magnitude has been calculated as the area of the landslides obtained from the landslide mapping and from the orthophotos. The resulting magnitude-frequency relation for reactivations has been used to derive the probability of landslide reactivation for a given volume. It has been compared with probability of landslide reactivation obtained from the rainfall threshold responsible for the reactivation of 4-large landslides located within the Tremp Basin as well. The reactivation date has been estimated by means of dendrogeomorphology and the rainfall threshold has been determined by means of ROC analysis. The susceptibility of first-time slope failures have been obtained using a deterministic model named SINMAP. The frequency for each susceptibility class has been calculated using the inventory of first-time failures identified in the field and by means of orthophotos. An algorithm to obtain the area of the earthflows larger than the pixel size has been developed through an automatic aggregation of pixels located within the same slope and having the same susceptibility class. The obtained magnitude-frequency relation of first-time failures has been compared with the one obtained from the mapped first-time failures. Finally, the magnitude-frequency matrix for hazard mapping of intact slopes has been defined. Concerning the rockfalls, a methodology to obtain the rockfall scar size distribution of a cliff has been defined. It has been assumed the rockfall scar volumes as proxy for the rockfall volumes. In that case, the distribution of rockfall scars has been calculated using a high resolution point cloud of the rockwall obtained by a terrestrial laser scanner and following. Several volume distributions have been calculated to take into account the different detachment mechanisms and the consequent range of detached volumes. Finally, a procedure has been developed to convert form statistical frequency (% of scar volumes), calculated in the previous step, to temporal frequency (annual number of the scar volumes). To this, the total volume of material lost has been computed using the afore-mentioned point cloud. The elapsed time within the total volume has been removed has been estimated by dating the initial surface, from which the current rockfall activity started, by means of terrestrial cosmogenic nuclide, 36Cl.
Degut al creixement exponencial de la població durant les últimes dècades, l’avaluació de la perillositat de colades de terra i despreniments i la seva zonificació han esdevingut eines fonamentals pel que fa a la planificació del territori, sobretot en zones muntanyoses. La perillositat degut a fenòmens de vessant va ser definida com la probabilitat d’ocurrència d’un fenomen potencialment danyí en una determinada àrea i per un determinat període de temps. D’aquesta manera, és necessari conèixer la probabilitat d’ocurrència (o freqüència) per cada tipus d’esllavissada i magnitud. L’objectiu d’aquesta tesis és el desenvolupament d’una metodologia objectiva, quantitativa i reproduïble que permeti l’obtenció de les relacions magnitud-freqüència per colades de terra, de mida mitja i gran i per despreniments. Aquest procediment s’ha aplicat a la Vall de Barcedana i la Serra del Montsec per grans colades de terra i despreniments, respectivament. Les dues àrees d’estudi estan situades dins de la Conca de Tremp (Pirineu Oriental). Pel que fa a les colades de terra, s’ha distingit entre 1) reactivacions i 2) vessants intactes. La freqüència de les reactivacions s’ha obtingut a partir de l’anàlisi d’11 grups d’ortofotos que cobreixen des del 1956 al 2013. La magnitud s’ha calculat com l’àrea de les trencades mitjançant la cartografia d’esllavissades i les ortofotos. La relació magnitud-freqüència resultant de les reactivacions ha servit per obtenir la probabilitat de reactivació per un determinat volum. Aquesta ha estat comparada amb la probabilitat de reactivació determinada a partir dels llindars de pluja que han donat lloc a la reactivació de 4 grans esllavissades, també situades dins la Conca de Tremp. Les dates de reactivació han estat aproximades mitjançant la dendrogeomorfologia i els llindars s’han determinat mitjançant l’anàlisi ROC. La susceptibilitat de les primeres trenades s’ha obtingut mitjançant un model determinista anomenat SINMAP. La freqüència per cada classe de susceptibilitat s’ha calculat mitjançant un inventari de primeres trencades identificades al camp i a través d’ortofotos. S’ha desenvolupat un algoritme per tal d’obtenir l’àrea de les colades de terra més grans que la mida del píxel a través de l’agregació automàtic de píxels situats en un mateix vessant i que presenten una mateix classe de susceptibilitat. Finalment, s’ha definit la matriu magnitudfreqüència per la zonificació de la perillositat dels vessants intactes. Pel que fa als despreniments, s’ha definit una metodologia per obtenir la distribució de volums de cicatrius de despreniments d’un penya-segat. S’ha assumit que els volums de cicatrius de despreniments poden ser una primera aproximació dels volum de despreniments. En aquest cas, la distribució de les cicatrius de despreniments s’ha calculat utilitzant un núvol de punts d’alta resolució de la paret obtingut amb un LIDAR terrestre. S’han calculat vàries distribucions de volums per tal de tenir en compte els diferents mecanismes de despreniment i el conseqüent rang de volums despresos. Finalment, s’ha proposat una metodologia per tal de convertir la freqüència estadística (% de volums de cicatrius), calculada en el pas anterior, a freqüència temporal (número anual de volums de cicatrius). Per això, el volum total de material desprès s’ha calculat mitjançant el núvol de punts, mencionat anteriorment. El període de temps durant el qual s’ha desprès tot el volum de material s’ha estimat mitjançant la datació de la superfície inicial a partir de la qual va començar l’actual activitat de despreniments. Aquesta datació s’ha fet mitjançant l’isòtop cosmogenic, 36Cl.
Debido al crecimiento exponencial de la población durante las últimas décadas, la evaluación de la peligrosidad de coladas de tierra y desprendimientos i su zonificación se ha convertido en herramientas indispensables para la planificación del territorio, sobretodo en zonas montañosas. La peligrosidad debido a fenómenos de vertiente fue definida como la probabilidad de ocurrencia de un fenómeno potencialmente dañino en una determinada área y en un determinado período de tiempo. Así, es necesario conocer la probabilidad de ocurrencia (o frecuencia) para cada tipo de deslizamiento y magnitud. El objetivo de esta tesis es el desarrollo de una metodología objetiva, cuantitativa y reproducible que permita la obtención de las relaciones magnitud-frecuencia para coladas de tierra, de tamaño medio y grande y para desprendimientos. Este procedimiento se ha aplicado en Valle de Barcedana y en la Sierra del Montsec para grandes coladas de tierra y desprendimientos, respectivamente. Las dos áreas de estudio están situadas dentro de la Cuenca de Tremp (Pirineo Oriental). En cuanto a las coladas de tierra, se ha distinguido entre 1) reactivaciones y 2) vertientes intactos. La frecuencia de las reactivaciones se ha obtenido a partir del análisis de 11 grupos de ortofotos que engloban des del 1956 hasta el 2013. La magnitud se ha calculado como el área de las roturas mediante la cartografía de deslizamientos y ortofotos. La relación magnitud-frecuencia de las reactivaciones ha permitido obtener la probabilidad de reactivación per un determinado volumen. Esta ha sido comparada con la probabilidad de reactivación determinada a partir de los umbrales de lluvia que han dado lugar a la reactivación de 4 grandes deslizamientos, también situados dentro de la Cuenca de Tremp. Las fechas de reactivación han sido aproximadas mediante la dendrogeomorfología y los umbrales se han determinado mediante el análisis ROC. La susceptibilidad de las primeras roturas se ha obtenido mediante un modelo determinista llamado SINMAP. La frecuencia para cada clase de susceptibilidad se ha calculado mediante un inventario de primeras roturas identificadas en el campo y a través de ortofotos. Se ha desarrollado un algoritmo para obtener el área de las coladas de tierra más grandes que el tamaño del píxel a través de la agregación automática de píxeles situados en una misma vertiente y que presentan una misma clase de susceptibilidad. Finalmente, se ha definido la matriz magnitud-frecuencia para la zonificación de la peligrosidad de las vertientes intactas. En lo que concierne a los desprendimientos, se ha definido una metodología para obtener la distribución de volúmenes de cicatrices de desprendimientos de un acantilado. Se ha asumido que los volúmenes de cicatrices de desprendimientos pueden ser una primera aproximación de los volúmenes de desprendimientos. En este caso, la distribución de las cicatrices de desprendimientos se ha calculado utilizando una nube de puntos de alta resolución de la pared obtenida con un LIDAR terrestre. Se han calculado varias distribuciones de volúmenes para tener en cuenta los diferentes mecanismos de desprendimiento y el consecuente rango de volúmenes desprendidos. Finalmente, se ha propuesto una metodología para transformar la frecuencia estadística (% de volúmenes de cicatrices), calculada en el paso anterior, en frecuencia temporal (número anual de volúmenes de cicatrices). Para esto, el volumen de material desprendido se ha calculado mediante la susodicha nube de puntos. El período de tiempo durante el cual se ha desprendido la totalidad del volumen de material se ha estimado mediante la datación de la superficie inicial a partir de la cual empezó la actual actividad de desprendimientos. Esta datación se ha hecho mediante el isótopo cosmogénico 36Cl.

In questa tesi è stata valutata la pericolosità e quindi il relativo rischio da crollo. In particolare riferendoci ad ammassi affioranti lungo tratti stradali sono stati considerati due metodi classificativi, che ci hanno permesso di evidenziare sezioni a diverso rischio. Le metodologie utilizzate per la classificazione sono: - RHRS Pierson et al. 1990; - RHRS Russell et al. 2008. Ogni metodologia utilizza particolari tabelle che restituiscono punteggi la cui sommatoria cumulativa costituisce il Total Hazard Risk Score caratteristico di ogni sezione. Dopo aver discusso i risultati ottenuti ed aver analizzato i fattori determinanti per la diversa caratterizzazione del tratto stradale in sezioni a diverso rischio, è stata analizzata la compatibilità e le differenze tra i due metodi classificativi adottati.

Il presente lavoro ha lo scopo di analizzare con il metodo Rockfall Hazard Rating System (Pierson et al, 1990) un tratto di strada lungo la SS612 nei comuni di Molina di Fiemme (Tn) e Anterivo (Bz) in tre zone distinte e valutarne il rischio rispetto ai fenomeni di crollo.

Scopo della tesi è l'analisi del rischio da caduta massi con Rockfall Hazard Rating System lungo la SP29 di Sovramonte (BL) e la SP19 di Lamon (BL). Sono stati utilizzati il metodo RHRS originale (Pierson et al., 1990) e il metodo RHRS modificato (P.Santi et al., 2009) per valutare gli aspetti geologici di dodici sezioni soggette a distacco di roccia insieme alle caratteristiche stradali. Con i punteggi ottenuti dallo studio di ogni sezione si è infine riusciti a fornire una scala di priorità per gli interventi di sistemazione.

Gli eventi sismici sono riconosciuti come una delle maggiori cause per l’innesco di frane (Keefer, 1984). Le frane sismo-indotte sono documentate sin dal IV secolo (Seed, 1968). È stata condotta un’analisi sulla distribuzione spaziale delle frane sismo-indotte nell’area circostante la sorgente sismogenetica per meglio comprendere il loro innesco in aree sismiche e per delimitare la massima distanza alla quale un sisma con data magnitudo possa indurre frane. Tuttavia, quando si applicano tali approcci a eventi storici si pone un problema legato al sottocampionamento delle frane più piccole, che possono essere obliterate dall'erosione e dall'evoluzione del paesaggio. Per questo motivo è importante caratterizzare accuratamente la distribuzione delle frane, in termini di dimensione, in funzione della distanza dalla sorgente sismica. Sono stati analizzati sei terremoti in tutto il mondo che hanno innescato un significativo numero di frane (Finisterre 1993, Northridge 1994, Niigata 2004, Wenchuan 2008, Iwate 2008 and Tohoku 2011) per meglio comprendere le relazioni esistenti tra la distribuzione spaziale delle frane, l’accelerazione di picco al suolo (PGA), la distanza dalla sorgente, il relief e le litologie presenti nell’area. Si è osservata una forte relazione tra la PGA e la dimensione delle frane, mentre una la relazione tra la loro dimensione e la distanza dalla sorgente non è altrettanto chiara, ciò legato all’interazione tra diversi fattori quali ad esempio il relief e la litologia. Sono state realizzate e analizzate le curve magnitudo-frequenza (MFC) per differenti distanze dall’area sorgente attraverso varie metodologie: stimatore di massima verosimiglianza per distribuzioni di tipo potenza cumulate (Clauset et al, 2009), stimatore di massima verosimiglianza per distribuzioni di tipo potenza non cumulate, regressione ai minimi quadrati per funzioni di tipo potenza non cumulate in scala logaritmica e stimatore di massima verosimiglianza per la distribuzione Double Pareto. Dalle analisi si è potuto osservare un decrescere della densità spaziale delle frane con la distanza, ma un basso impatto della dimensione delle frane. Inoltre la funzione Double Pareto è stata scelta come miglior strumento per il fittaggio dei dati (Valagussa et al, 2014). Allo scopo di definire il rischio legato alle frane sismo-indotte è stata sviluppata una metodologia per la zonazione probabilistica quantitativa del rischio da frane da crollo (Valagussa et al, 2014). Il metodo è stato applicato e dimostrato nell’area del Friuli (Apli orientali) colpita da un terremoto di magnitudo 6.4 nel 1976. Quattro inventari sono stati realizzati sia tramite attività di terreno che da dati storici. La metodologia si basa sul vettore di rischio tridimensionale (RHVmod) le cui componenti includo l’energia cinetica, l’altezza di volo e la frequenza annua. I primi due valori sono calcolati per ogni cella del versante per mezzo del programma Hy-STONE. La frequenza annua è invece determinata moltiplicando la frequenza d’innesco annua per il numero di transiti simulati in ogni cella. La frequenza d’innesco annua è calcolata combinando l’area instabile, calcolata per 10 differenti scenari con differente frequenza annua di occorrenza sulla base di caratteristiche morfometriche e sismiche, e la curva magnitudo-frequenza relativa dei blocchi identificati da attività di terreno. Una serie di analisi discriminanti sono state condotte per determinare le variabili che controllano l’area in frana, sulla base degli inventari redatti e di DEMs a differenti risoluzioni (1 e 10m). L’analisi ha dimostrato il ruolo rilevante della curvatura nella definizione dell’area instabile. Per verificare la validità della mappa di PGA utilizzata nelle analisi, una nuova mappa è stata redatta sulla base delle Precarious Balanced Rocks identificate sul terreno.
Earthquakes have been recognized as a major cause of landsliding (Keefer, 1984), and landslides triggered by earthquakes have been documented since the IV century (Seed, 1968). The spatial distribution of earthquake-induced landslides around the seismogenetic source has been analysed to better understand the triggering of landslides in seismic areas and to forecast the maximum distance at which an earthquake, with a certain magnitude, can trigger landslides. However, when applying such approaches to old earthquakes one should be concerned about the undersampling of smaller landslides, which can be cancelled, by erosion and landscape evolution. For this reason, it is important to characterize carefully the size distribution of landslides as a function of distance from the earthquake source. I analysed six earthquakes in the world that triggered significant amount of landslides (Finisterre 1993, Northridge 1994, Niigata 2004, Wenchuan 2008, Iwate 2008 and Tohoku 2011) to better understand the relation between the spatial distribution of the landslides, the peak ground acceleration (PGA), the distance from the sources, the relief and the lithologies of the area. I observed a strong relationship between landslides size and PGA, while the relationship between the distance from the source and the landslide size distribution is not clear, due to the interaction of different factors such as relief and lithology. I also developed magnitude frequency curves (MFC) for different distances from the source area by using different methods, such as: the maximum likelihood estimator of cumulative power-law distribution (Clauset et al, 2009); the maximum likelihood estimator of non-cumulative power-law function; the least square regression of non-cumulative log power-law function and the maximum likelihood estimator of Double Pareto distribution. I observed a decrease of the spatial density of landslides with distance, with a small effect of the size of these landslides. I also identify the Double Pareto function as the best tool for the fitting of the data (Valagussa et al., 2014a). In order to define the hazard due to earthquake-induced landslides, I developed a methodology for quantitative probabilistic hazard zonation for rockfalls (Valagussa et al., 2014b). I applied and demonstrated the method in the area of Friuli (Eastern Italian Alps) that was affected by the 1976 Mw 6.5 earthquake. Four rockfall datasets have been prepared from both historical data and field surveys. The methodology relies on a three-dimensional hazard vector (RHVmod), whose components include the rockfall kinetic energy, the fly height, and the annual frequency. The values of the first two components are calculated for each location along the slope using the 3D rockfall runout simulator Hy-STONE. The rockfall annual frequency is assessed by multiplying the annual onset frequency by the simulated transit frequency. The annual onset frequency is calculated 2 through a procedure that combines the extent of unstable areas, calculated for 10 different seismichazard scenarios with different annual frequencies of occurrence, and the magnitude relativefrequency relationship of blocks as derived from the collected field data. For each annual frequency of occurrence, the unstable area is calculated as a function of morphometric and earthquake characteristics. A series of discriminant-analysis models, using the rockfall datasets and DEMs of different resolution (1 and 10 m), identified the controlling variables and verified the model robustness. In contrast with previously published research, I show that the slope curvature plays a relevant role in the computation of the unstable area. To ensure the validity of the peak ground acceleration used as seismic parameter in the discriminant function, I also try to define a map of PGA based on the precarious balanced rocks surveyed on the field.

De nombreuses incertitudes liées aux mécanismes d'interaction entre les blocs rocheux et le versant naturel lors des chutes de blocs persistent ; la prévision de tels événements reste de ce fait encore incertaine. Néanmoins, les outils numériques et la puissance de calcul ne cessent d'évoluer. Si, auparavant, les calculs trajectographiques étaient restreints à des géométries simplifiées et à des mouvements balistiques en deux dimensions, il devient désormais possible d'y intégrer des raffinements tels que la forme complexe des blocs, des modèles numériques tridimensionnels de terrain d’une grande définition ou une prise en compte fine des mécanismes dissipatifs au niveau du point d'impact entre le bloc et le versant de propagation.L’objectif principal de la thèse est d’analyser, avec un code numérique discret en trois dimensions, l’influence des paramètres de forme et d’interaction sur la nature du rebond dans un contexte d’ingénierie. Nous présentons tout d’abord une méthodologie d'identification et d'étude de sensibilité des paramètres de contact, élaborée et validée à partir d’expérimentations de laboratoire. Cette méthodologie a été appliquée par la suite à deux expérimentations de chute de blocs menées sur sites réels à moyenne et à grande échelle.L’étude réalisée à moyenne échelle a permis de confronter le modèle numérique à des données obtenues lors d'une campagne expérimentale sur voies ferroviaires commanditée par la SNCF et menée en collaboration avec IRSTEA. Les analyses qui ont été réalisées ont porté sur les vitesses d’impact des blocs avec le ballast et les distances de propagation.L’étude menée à grande échelle s’appuie sur plusieurs séries de lâchés de blocs réalisées sur le site expérimental de la carrière d'Authume dans le cadre d’un Benchmark proposé dans le cadre du Projet National C2ROP. L’objectif principal du Benchmark est de tester et de comparer entre eux des logiciels trajectographiques, des codes de calculs numériques et les pratiques d’ingénierie pour en définir la pertinence et les domaines de validité. Dans le cadre de la thèse, ce travail a été conduit en plusieurs phases (à l’aveugle puis avec des données partielles mesurées lors de la campagne d'essais) et nous présentons l'évolution de ces analyses à l'issue de chacune des phases. L’étude a porté principalement sur les vitesses, les hauteurs et les énergies de passage des blocs en certains points du profil de propagation, ainsi que sur les positions d’arrêt des blocs. Une étude sur l'influence de la forme des blocs sur les distances de propagations est également présentée.Enfin, un Benchmark interne réalisé au sein de l'entreprise IMSRN montre l’importance, sur les analyses, de l'expertise de l'opérateur, et des conséquences de l'utilisation de différents outils trajectographiques (en 2D et en 3D). Ces travaux mettent en lumière les problématiques actuelles auxquelles sont souvent confrontés les bureaux d'études et les ingénieurs en charge des études de risques
Numerous uncertainties related to the machanical interaction between rock boulders and the natural slope during block falls persist; and the forecast of such events is therefore still uncertain. Nevertheless, digital tools and computing power are constantly evolving. Previously, trajectory calculations were restricted to simplified geometries and two-dimensional ballistic movements, but it is now possible to incorporate refinements such as the complex shape of the blocks, three-dimensional numerical models of terrain of large sizes, as well as a better accounting of the dissipative mechanisms at the point of impact between the block and the run-out slope.The main objective of this work is to analyze, with a discrete elements code in three dimensions, the influence of the shape and interaction parameters on the nature of the rebound in an engineering context. We first present a methodology for identifying and studying the sensitivity of contact parameters, developed and validated from laboratory experiments. This methodology was subsequently applied to two block fall experiments conducted on medium and large real-scale scenarios.The study conducted on a medium scale allowed the numerical model to be compared with data obtained during an experimental rockfall tests campaign commissioned by the SNCF and conducted in collaboration with IRSTEA in a railway. The analyzes that were carried out mainly focused on the impact velocities of the blocks with ballast and propagation distances.The large-scale study is based on a series of block releases performed at the experimental site (Authume quarry, France) as part of a Benchmark proposed inside the National Project C2ROP. The mainly goal of this Benchmark is to access and compare trajectory softwares, numerical computation codes and engineering practices to define their relevance and validity domains. As part of the thesis, this work was conducted in several phases (blind phase and then conducted taking in account partial data measured during the experimental tests) and we present the evolution of these analyzes at the end of each one of these phases. The study focused on the velocities, heights and energies of the blocks at certain points of the propagation profile, as well as on the stopping positions of the blocks. The influence of block shapes on run-out distances is also presented.Lastly, an internal Benchmark performed within the IMSRN company shows the importance, on the analyzes, of the expertise of the operator, and the consequences derived from the application of different trajectography tools (in 2D and in 3D). This work highlights the current issues that are often faced by engineering offices and engineers in charge of risk quantification

Les éboulements rocheux de volume intermédiaire (103-105 m3) posent un problème sérieux dans les régions montagneuses en raison de leur fréquence d'occurrence relativement élevée et de leur fort pouvoir destructeur. En conséquence, il est difficile de mener des travaux de protection pour réduire l'aléa, ce qui souligne le besoin de techniques de suivi et d'alerte précoce avant la rupture. Après l'éboulement, peu d'informations quantitatives sont disponibles sur la phase de propagation en raison de la soudaineté du phénomène et de sa localisation dans des pentes raides et difficiles d'accès. Dans ce travail de thèse, une approche expérimentale est proposée pour extraire des informations à partir d'enregistrements de signaux sismiques durant les phases pré- et post-rupture d'éboulements.La première partie de ce travail vise à tester la pertinence des vibrations ambiantes pour le suivi temporel de la réponse dynamique de compartiments rocheux lors de la phase pré-rupture. Cette technique (couramment employée en génie civil pour le suivi de l'intégrité des structures) permet d'extraire les fréquences de résonance d'une structure, dont la décroissance peut traduire l'endommagement. Une étude antérieure menée sur une colonne calcaire instable a montré une décroissance d'environ 30% de la fréquence fondamentale de résonance (f1) environ deux semaines avant la rupture, interprétée comme une diminution de la rigidité du contact avec le massif stable adjacent
Mid-size rockfalls (103-105 m3) represent a substantial hazard in mountainous areas, because of relative high rate of occurrence and destructive power. Consequently, few protection means can be applied, emphasizing the need for monitoring techniques and early warning prior to the collapse. After the rupture, quantitative information on the rockfall propagation phase is scarce, owing to their suddenness and location in steep and rugged slopes. In this thesis work, an experimental approach is proposed to derive valuable information from seismic records during rockfall pre-rupture and post-rupture phases. The first part of this work aims at testing the applicability of the ambient vibration technique to monitor unstable rock compartments dynamic response in the pre-rupture phase. This technique (commonly employed in civil engineering for structural health monitoring) reveals the resonant frequencies of a structure, a decrease in frequency revealing potential damage. A previous case study of an unstable limestone compartment brought to light a #30% decrease in fundamental resonant frequency (f1) two weeks before the collapse. Following this innovative work, we selected and instrumented four prone-to-fall medium-size rock compartments located in the Occidental Alps, showing various geological contexts (limestones, argillite and shale-sandstone series), deformation patterns and failure mechnisms. Ambient vibrations recorded on-site revealed caracteristic seismic noise features. Spectral peaks were observed and attributed to resonant frequencies of the rock compartments, the fundamental resonant frequency (f1) showing clear polarization parallel to the line of maximum slope gradient, and perpendicular to the main bounding fracture observed at most of the sites. Similar findings were made for an unstable rock compartment located in a volcanic caldera, characterized by rapid morphological changes and intense rockfall activity. The dynamic response of the rear fracture network was explored, showing that spectral content of seismic noise is controlled by the caldera structure in the 0.5-5 Hz range. The direction of vibration is polarized perpendicularly to the fractures, while vibration amplitudes are linked to compartment uncoupling from the rock massif. In this case, the physical origin of seismic noise amplification may be due to complex 2D or 3D resonance effects. For the four alpine sites, the fundamental frequency f1 was monitored over more than one year, showing fluctuations clearly correlated with temperature oscillations. The thermal control over f1 is highly complex, showing both positive and negative correlations, depending on site morphology and destructuration, as well as on the studied oscillations periods (daily or seasonal). No change in fundamental frequency resulting from damage was observed over this time span. One site, characterized by intense rock fracturing and a deep-open rear fracture, showed high f1 sensitivity to temperature changes. Thermo-mechanical numerical simulations revealed that both material contraction-dilation and thermal dependancy of the elastic modulus control f1 fluctuations. In addition, high amplitude seasonal f1 oscillations were explained by ice formation in the rear fracture. A criterion was developped to separate thermal-induced f1 fluctuations from damage effects, under the hypothesis that thermal sensitivity of a rock compartment increases towards failure. The second part of this work relates to the post-rupture phase of rockfalls. The seismic records generated by two mid-size rockfalls {one natural, one provoked{ that occured in the same place were analyzed, showing complex enveloppe and spectrogram features. Both events showed close magnitude, duration and spectral content. The seismic signals of the provoked event were calibrated using video shots, allowing estimation of fallen material velocity during the successive propagation phases

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

De nombreuses incertitudes interviennent lors de l’évaluation de l’aléa de départ des éboulements rocheux. Ce mémoire se propose de les étudier, en suivant la typologie de Baecher & Christian (2005) qui identifie (1) l’incertitude de décision, (2) l’incertitude de connaissance et (3) l’incertitude aléatoire. L’incertitude de décision intervient au travers de l’évaluation de l’aléa par expertise. Nous avons mis au point une expérimentation visant à étudier l’influence du niveau d’expertise de la personne en charge de l’étude et de la méthode utilisée (qualitative et quantitative) sur l’évaluation de l’aléa. Nous avons montré que l’utilisation d’une méthode qualitative permet de guider la pensée et de réduire la dispersion des niveaux d’aléas finaux, ce qui n’est pas le cas d’une méthode quantitative. Nous montrons également que dans des cas spectaculaires, l’expérience de l’ingénieur lui permet de ne pas surévaluer l’aléa, et que pour des cas plus classiques, il n’y a pas d’influence du niveau d’expertise dès lors que la méthode est suffisamment détaillée. L’incertitude aléatoire se manifeste par la variabilité temporelle des éboulements rocheux. Un travail sur des bases de données a été entrepris. Il a permis de mettre en évidence une corrélation statistique entre les éboulements rocheux et certains facteurs météorologiques (pluies et températures). Une méthode évaluant la probabilité d’occurrence des éboulements en fonction de l’intensité des pluies ou la valeur des températures a alors été développée. Elle peut être considérée comme un outil d’aide à la décision dans la gestion du risque. Un travail sur ces bases de données a également permis de montrer l’existence d’une composante de bruit de fond aléatoire, ne montrant aucune corrélation statistique, caractérisée par le fait que le temps qui sépare deux chutes de blocs suit une loi de Poisson. L’incertitude de connaissance résulte d’un manque d’informations concernant, en particulier, les facteurs préparatoires. Afin de mieux appréhender ces incertitudes, des modèles numériques (éléments distincts - UDEC) de glissement d’un bloc sur un plan incliné, dépendants de la présence et de la proportion de ponts rocheux, ont été réalisés. Ils ont permis de montrer l’existence de deux phases dans la rupture, contrôlées par les reports des contraintes le long du joint entre le bloc et le plan, à mesure que de la rupture des ponts rocheux se propage. Cependant, ces deux phases ne se retrouvent pas dans l’étude des déplacements du bloc. Nous montrons également l’influence de la position des ponts rocheux sur la vitesse de propagation de la rupture en fonction de la pente. Ces travaux fournissent un outil opérationnel et des indications sur le processus d’évaluation de l’aléa qui pourraient aider l’ingénieur en charge d’une étude d’aléa à justifier et à affiner son estimation
The present dissertation proposes to study uncertainties in rockfall hazard assessment process, on the basis of the Baecher & Christian typology (2005), which identifies (1) decision uncertainties, (2) knowledge uncertainties, and (3) natural variability. Decision uncertainties are due to the subjectivity of experts’ assessment. An experiment has been realized in order to evaluate the influence of the expertise level, and the chosen method (qualitative or quantitative) on the rockfall hazard. The rockfall hazard levels obtained by the qualitative method are quite uniform while the quantitative method produces more disparate results. We have shown that, classically, the expertise level has no influence on the assessment if the method is precisely detailed. In the case of spectacular sites, experts do not overestimate the hazard. The natural variability is associated to the temporal variability of the rockfalls. We have studied the statistical correlation between meteorological and rockfall databases. We have developed a method that takes into account the probability of occurrence of the studied triggering factor (rainfalls and temperatures). This new approach is easy to use, and also helps to determine the conditional probability of rockfall according to a given meteorological factor. This approach will help to optimize risk management in studied areas based on their meteorological conditions. A work on these databases also has allowed the unpredictability of the rockfalls to be highlighted. Indeed, the delay between two rockfalls follows a Poisson distribution. Knowledge uncertainties may concern the preparatory factors. We have studied them with numerical models of a rock block sliding along a planar joint, depending on the proportion and position of rock bridges (distinct elements - UDEC). Two stages of the failure process have been highlighted; they have been controlled by the stress redistribution induced by the failure, and the propagation of the rock bridges. However, these two phases are not identified when studying block displacements. We also have shown the influence of the position of rock bridges on the propagation of failure. This research provides an operational tool, and guidelines on assessment process that may help engineers in charge of a rockfall risk analysis to justify and refine the obtained risk estimations

Les sols sont utilisés dans différents dispositifs de protection contre les chutes de blocs rocheux : pour couvrir des structures exposées, telles que les tunnels ou les galeries, ou construire des merlons. Une campagne d’essais expérimentaux instrumentés a été menée pour compléter l’observation des phénomènes, en particulier pour mieux caractériser la distribution spatio-temporelle de pression induite à l’interface entre la couche de sol protectrice et la structure, dans différentes configurations d’impact. Plusieurs configurations d’impacts ont été considérées, caractérisées par l’épaisseur de sable (D), le diamètre équivalent du bloc rocheux (B, ou sa masse) et sa hauteur de chute libre (H). L’étude paramétrique expérimentale a comporté 43 essais, combinant systématiquement différentes valeurs de D, B et H de l’ordre de celles rencontrées en pratique. Suite au dépouillement des mesures, une expression de la pression induite à l’interface sol-structure pendant un impact au sommet de la couche de sol protectrice a été proposée. La démarche exposée pour établir, dans une configuration d’impact D, B et H, les valeurs des paramètres qui caractérisent les cinq grandeurs décrivant la distribution spatio-temporelle de pression induite à l’interface sol-structure, peut être appliquée à d’autres natures de sols ou densités de compactage. Par ailleurs, un modèle numérique tridimensionnel simple de calcul en déformations, en dynamique explicite, a été développé. Le comportement en déformations du sol a été représenté par un modèle élastoplastique, avec critère de rupture de Mohr-Coulomb et faible dilatance. Les calculs ont été réalisés avec le logiciel ABAQUS. Enfin, une méthode de dimensionnement des couches de sol en protection de structures a été proposée. Cette méthode comporte deux étapes : (1) Pour la configuration d’impact B, D, H considérée, utiliser l’expression développée dans cette étude pour définir la distribution spatio-temporelle de pression induite à l’interface sol-structure, puis (2) Calculer en dynamique la structure soumise à cette impulsion de pression
An extensive experimental parametric study has been carried out to characterize how impact loads of low velocity (lower than 100 km/h) are transmitted to a structure through a protective sand layer. Different rock fall conditions have been considered, corresponding to actual conditions in current practice. The experimental program consisted of 43 full scale impact tests on a sand layer protecting a concrete foundation mat, combining three sand layer thicknesses (1, 1.5 and 2 m), impacting blocs of equivalent diameters in the range of 0.42 to 1.79 m and five free falling heights, up to 33 m. Based on the analysis of pressure cells measurements for the different rock fall conditions, the pressure induced at the interface between the protective sol layer and the structure by an impact was expressed in terms of impact conditions, defined by layer thickness (D), size of the impacting bloc (B) and height of free fall (H). Procedures to derive the model parameters from the tests are explained in detail. A numerical model was developed to simulate an impact on a structure protected by a soil layer based on a deformation analysis approach. The Finite Element code ABAQUS was used. The bloc, the soil and the structure were considered as different bodies, having contact conditions between them. The stress‐strain relationship in the soil was assumed to be elastoplastic. Friction angle and dilation angles were derived from laboratory tests on the sand. The elastic modulus was assumed constant, equal to usual values for compacted sands. An approach is proposed for the design of soil layers to protect structures from impacting loads due to rock falls

Parmi les mouvements de terrain, les éboulements rocheux restent le danger le plus imprévisible et le plus fréquent en région alpine. Dans un contexte d'urbanisation croissante des régions montagneuses, les éboulements représentent un risque croissant pour les communautés locales et les infrastructures. Cette thèse vise à développer une association pertinente de méthodes pour la surveillance des éboulements en couplant des mesures de relief à un suivi sismologique, afin d’améliorer la compréhension de la dynamique des éboulements. Ce travail a été principalement réalisé dans le massif de la Chartreuse (Isère, Alpes Françaises), et en particulier sur deux falaises, le mont Saint-Eynard et le mont Granier. Par photogrammétrie, nous avons obtenu des Modèles Numériques de Terrain (MNTs) des falaises. Ce suivi nous a permis de réaliser des inventaires de chutes de blocs et des analyses de fréquence d'occurrence. Cela nous a également fourni des informations sur les emplacements des éboulements ainsi que leurs configurations structurales. L’association des MNTs et du suivi sismique des éboulements nous a permis d’étudier les relations entre les propriétés des éboulements (emplacement, volume, géométrie, propagation, etc.) et le signal sismique induit par ceux-ci. Les caractéristiques des signaux sismiques (durée et énergie, contenu fréquentiel, forme de l’enveloppe) diffèrent selon le mode de propagation des évènements (écoulement en masse, chute libre, glissement, rebondissement, …). Une sélection d’évènements ayant le même type de propagation permet d’obtenir une caractérisation plus précise des propriétés des éboulements que si l’on mélange différents types d'événements. Dans le cas d’éboulements subissant une chute libre, nous avons analysé le signal sismique des phases de détachement et du premier impact. Nous avons obtenu des relations entre certains paramètres des signaux sismiques et l'énergie potentielle des éboulements, leur hauteur de chute libre ou leur volume. Pour les événements de type écoulement en masse, nous avons observé une loi d'échelle entre l'énergie sismique d'un éboulement et son volume. En couplant les MNTs et les enregistrements sismiques, nous sommes ainsi en mesure de reconstruire le déroulement des éboulements avec une datation précise et une estimation de volume correcte. Des lâchers contrôlés de blocs ont été réalisés en laboratoire et in-situ pour élargir nos observations sur les éboulements de falaise
Amongst mass wasting events, rockfalls remain the most unpredictable and the most frequent hazard in the alpine region. In a context of growing urbanization in mountainous regions, rockfalls represent an increasing risk for local communities and infrastructures. This thesis aims to develop an association of relevant methods for rockfall monitoring. One objective of this thesis is to associate topography measurement and seismological monitoring in order to improve significantly in understanding rockfalls dynamics. This work was mainly carried out in the Chartreuse massif (Isère, French Alps), and in particular two cliffs, Mount Saint-Eynard and Mount Granier. Using photogrammetry, we acquired diachronic Digital Elevation Models (DEMs) of the cliffs. Such monitoring enables us to carry out rockfall inventories and occurrence frequency analysis. It also provides us information on rockfall locations and their structural configurations. Combining DEMs and rockfall seismic monitoring allowed us to study relations between rockfall properties (location, volume, geometry, propagation, etc.) and the induced seismic signal. Characteristics of the seismic signal (duration and energy, frequency content, envelope shape) vary depending on the event propagation mode (mass-flow, free-fall, sliding, bouncing …). Selecting events with the same propagation type provides a more accurate characterization of rockfalls properties than when mixing different types of events. For free-falling rockfalls, we analyze the seismic signal of the detachment phases and first impacts. We found relations between seismic signals parameters and rockfalls potential energy, free-fall heights, and volumes. For mass-flow type events, we found a scaling law between rockfalls seismic energy and their volumes. By coupling DEMs and seismic records, we can reconstruct rockfall sequence with accurate timing and correct volume estimations. Controlled block releases were realized in laboratory and on-site to widen our observations on rockfall events

Cette thèse Cifre s’intéresse au comportement sous impact de structures de protection issues de la technologie Bloc Armé® proposée conjointement par Géolithe Innov et Géolithe. La structure est composée de blocs en béton liaisonnés par des armatures métalliques verticales et horizontales. L’innovation principale réside dans le système d’armatures qui assure un liaisonnement des blocs et confère à la structure une capacité à répartir les efforts et à dissiper de l’énergie.Des essais à échelle réelle permettent de caractériser la réponse dynamique de la structure selon deux types d’essais. Premièrement, la structure mise en œuvre horizontalement sur une couche support est soumise à des impacts à haute énergie (2000 kJ) par lâchers verticaux d’un impactant. Deuxièmement, des essais à énergie moindre (125 kJ) sont réalisés par impact horizontaux sur un mur vertical de dimensions limitées. Des modèles réduits de la structure, à l’échelle ¼, sont également impactés, au laboratoire. Cette campagne est l’occasion de tester de nombreuses configurations de mur dans des conditions d’impact variées. Ces campagnes expérimentales permettent d’illustrer les mécanismes par lesquels une telle structure articulée se déforme sous sollicitation dynamique localisée. Les différents modes de déplacement des murs et certains phénomènes dissipant l’énergie d’impact sont mis en évidence et quantifiés. Les nombreuses mesures faites lors des essais constituent une importante base de données expérimentales, pour accompagner le développement du modèle numérique.Un modèle numérique aux différences finies est proposé pour cette structure. Une approche réaliste est suivie pour la modélisation : chacun des éléments de la structure est modélisé explicitement. Un modèle simple est volontairement considéré pour le béton constitutif des blocs. Le modèle est calibré d’après des valeurs issues de la littérature et des mesures faites spécifiquement. La confrontation des résultats de simulations d’impact avec les résultats expérimentaux témoigne d’une bonne aptitude du modèle à reproduire le comportement dynamique global de la structure et à estimer son déplacement résiduel, en particulier. Le modèle permet de quantifier la dissipation d’énergie découlant de la plastification du béton des blocs et des frottements dans la structure. Le modèle est ensuite utilisé pour simuler la réponse de murs de géométries variées et sous impact à haute énergie. Les perspectives de ce travail sont de proposer un modèle robuste capable de simuler des impacts à énergie de l’ordre de 5 000 kJ sur des ouvrages dont la géométrie pourra être complexe
This Cifre thesis investigates the impact response of protective structures based on the Bloc Armé® technology, developed by Géolithe Innov and Géolithe. This structure is made of concrete blocks linked by vertical and horizontal metal reinforcements. The main innovation lies in the reinforcement system which ensures the bonding of the blocks and gives the structure an ability to distribute the forces and dissipate energy.Two types of real-scale experiments permit to characterize the dynamic response of the structure. Firstly, the structure laid horizontally on a support layer is subjected to high- energy impacts (2000 kJ) by freely dropping of a projectile. Secondly, lower energy impact tests (125 kJ) are carried out by horizontal impact on a vertical wall of limited dimensions. Reduced models of the structure, at ¼ scale, are also tested under impact in the laboratory. This campaign permits to test many walls of different configurations under various impact conditions. These experimental campaigns illustrate the deformation mechanisms under localized dynamic solicitation for this kind of articulated structure. The different displacement modes of vertical walls and several phenomena dissipating impact energy are highlighted and quantified. The numerous measurements made during the tests constitute an important experimental database, supporting the development of the numerical model.A numerical model, developed with the finite differences method, is proposed for this structure. A realistic approach is followed for the modeling: each element of the structure is modeled explicitly. A simple model is deliberately considered for the concrete constituting the blocks. The model is calibrated based on values from the literature and measurements made specifically. The comparison of impact simulations results with experimental ones attests of the ability of the model in reproducing the global dynamic behavior of the structure and in estimating its residual displacement, in particular. The model quantifies the energy dissipation resulting from plasticization of the concrete blocks and from friction in the structure.The model is then used to simulate the response of walls of various geometries and under high energy impact. The outlooks of this work are to propose a robust model able to simulate the structure response to impacts with energies up to 5,000 kJ, considering structures with complex geometries

Les chutes de blocs constituent un aléa naturel majeur dans les Alpes françaises en raison de leur probabilité d'occurrence spatiale et temporelle très élevée. Les forêts peuvent constituer une solution naturelle et efficace pour atténuer ce phénomène tout en protégeant les populations et leurs infrastructures. Cependant, ce service écosystémique peut être perturbé par d'autres aléas naturels comme les feux de forêts, susceptibles d'être plus fréquents et intenses dans le contexte actuel et futur de changements climatiques.Cette thèse propose ainsi d'évaluer les effets des incendies sur la capacité de protection des forêts contre les chutes de blocs dans les Alpes françaises.Une méthodologie pour évaluer la capacité de protection d'une forêt contre les chutes de blocs est d'abord développée et consiste à utiliser des simulations de propagation de chutes de blocs réalisées sur 3886 placettes forestières des Alpes françaises pour calculer trois indicateurs quantitatifs évaluant la réduction de la fréquence (BARI), de l'intensité (MIRI) et la réduction globale (ORPI) de l'aléa chutes de blocs dues à la présence d'une forêt. Ces indicateurs sont utilisés pour identifier les variables forestières prépondérantes pour évaluer la capacité de protection : la longueur boisée sur le versant, la surface terrière et le diamètre moyen. Les peuplements présentant une distribution hétérogène des diamètres et composés de plusieurs essences offrent généralement une meilleure protection que les peuplements monospécifiques et réguliers, soulignant ainsi l'influence de la diversité forestière. Cette thèse montre ainsi que les taillis présentent les capacités de protection les plus élevées, suivis par les futaies feuillues et les futaies mixtes ; les peuplements résineux venant en dernier.Les évolutions spatiales et temporelles des conditions climatiques favorables aux incendies, étudiées sur la période 1959-2015, révèlent un contraste majeur entre les Alpes du Sud qui ont connu une forte augmentation (en intensité, fréquence, durée et saisonnalité) surtout à haute altitude, et les Alpes du Nord, où une légère hausse est observée à basse altitude, mais aucune tendance significative n'est observée à haute altitude. Ces résultats sont ensuite utilisés pour définir trois types de feux (d'hiver, d'été moyen et d'été très sec) pour lesquels la mortalité post-incendie est étudiée à l'échelle de l'arbre et du peuplement forestier. Ces analyses montrent que seuls les feux d'été sont susceptibles d'affecter significativement les peuplements, en particulier à basse altitude où les peuplements feuillus (notamment les taillis) dominent.L’effet des incendies sur la capacité de protection des forêts est évalué en comparant les simulations de propagation de chutes de blocs sans feu aux simulations après chaque type de feu pour lesquelles les arbres avec une forte probabilité de mortalité post-feu ne sont pas pris en compte. Les valeurs de ORPI pour chaque placette forestière et chaque type de feu sont ainsi calculées et comparées au scénario de référence sans feu, permettant ainsi d'évaluer quantitativement la réduction de la capacité de protection. Les peuplements de basse altitude, soumis à des conditions climatiques plus chaudes et sèches, présentent des réductions de la capacité de protection après des feux d'été de l'ordre de 60 à 100 %. Il s'agit principalement de taillis et de futaies feuillues. À plus haute altitude, la réduction est de l'ordre de 30 à 65 %.En conclusion, ce travail de thèse propose une méthode originale pour quantifier la capacité de protection d'une forêt contre les chutes de blocs avant et après un incendie et alimente les connaissances sur ces deux aléas naturels et les risques associés. L'analyse multi-aléas conduite en fin de thèse permet d'appréhender les effets cascades potentiels à l'échelle du peuplement forestier et de quatre territoires bioclimatiquement homogènes des Alpes françaises
Rockfalls are a major natural hazard in the French Alps due to their high probability of spatial and temporal occurrence. Forests constitute an efficient nature-based solution to mitigate this hazard while protecting human lives and assets. However, this ecosystem service may be disrupted by others natural hazards such as wildfires likely to be more frequent and intense in the current and future context of climate changes.This PhD thesis proposes to assess the effects of fires on the protection capability of forests against rockfalls in the French Alps.A methodology to evaluate the protection capability of a forest against rockfalls is first developed. It consists in modeling rockfalls propagations on 3886 forest plots taken in the French Alps to calculate three quantitative indicators that assess the reduction of the frequency (BARI), the intensity (MIRI) and the overall reduction (ORPI) of rockfalls due to the presence of a forest. These indicators are used to identify the predominant forest variables for assessing the protective effect: the length of forest along the slope, the basal area and the mean diameter. Forest stands with a heterogeneous distribution of diameters and made up of several tree species generally offer a better protection than monospecific and regular stands, thus underlining the influence of forest diversity. This work shows that coppices have the highest protection capabilities, followed by hight stands dominated by deciduous species and mixed stands; coniferous stands coming last.Spatio-temporal trends in fire weather in the French Alps are investigated over the period 1959-2015 and reveal a major contrast between Southern Alps which experienced a strong increase (in intensity, frequency, duration and seasonality) especially at high elevation, and Northern Alps, where a slight increase at low elevation and no significant trends at high elevation are observed. These results are then used to define three types of fires (winter, summer, and dry summer) for which post-fire tree mortality is studied at the tree and forest stands levels. These analyses show that only summer fires are likely to significantly affect the forest ecosystems, particularly at low elevations where deciduous stands (especially coppice) dominate.The effect of fires on the protection capabilities of forests is assessed by comparing rockfalls propagation simulations without fire to simulations after each type of fire in which the trees with a high post-fire mortality are not taken into account. The ORPI values for each forest plot and fire type are thus calculated and compared to the reference scenario without fire thus making it possible to quantitatively assess the reduction of the protection capabilities. Low elevation stands, subject to warmer and drier climatic conditions, show reductions of the protective effect in the range 60-100%. It mainly concerns coppices and deciduous stands. At high elevation, the reduction is in the range 30- 65%.In conclusion, this PhD thesis proposes an original method to quantify the protection capabilities of a forest against rockfalls before and after a fire and improve the knowledge of these two natural hazards and their associated risks. The multi-hazard analysis conducted at the end of the thesis makes it possible to understand the potential cascading effects in the main forest types and for four bioclimatically homogeneous territories of the French Alps

Thesis (M.S.)--University of Tennessee, Knoxville, 2002.
Title from title page screen (viewed Feb. 28, 2003). Thesis advisor: Eric Drumm. Document formatted into pages (v, 148 p. : ill. (some col.)). Vita. Includes bibliographical references (p. 27-29).

碩士
國立交通大學
土木工程系
87
Rockfall often occurs along mountainside road slopes, especially during or after a heavy rainfall. Occasionally, the occurrence of a rockfall results in traffic interruption, property damage, and personal injury or death. The consequence of a rockfall incidence may be very serious and unacceptable for a community. The hazard potential of a rockfall depends on various factors including geology, topography, and weather, among many environmental factors. In the conventional approach, the hazard potential of rockfall is usually evaluated in a deterministic manner. Compared to other aspects of geotechnical engineering, the rockfall problem has a higher degree of uncertainty. It seems reasonable to take the probabilistic nature of rockfall problem into account. This thesis makes use of reliability analysis to investigate the probability of rockfall hazard. It also examines the influence of rainfall on hazard potential. By collecting relevant information concerning the factors that affect the rockfall hazard, this thesis attempts to establish a probabilistic model for evaluating rockfall hazard associated with the condition of rainfall. It establishes an empirical correlation between the minimum rockfall hazard rating and rainfall characteristics (including the cumulative rainfall and the daily rainfall at the time of rockfall). The probability of rockfall is calculated from the safety margin (the difference between the threshold index and the rockfall potential index). The threshold index is assumed normally distributed; it is calibrated from real rockfall records using an optimization procedure. The proposed approach is applied in evaluating the rockfall hazard along the central cross-ridge route. The comparison of the predicted results and the actual case records shows very good agreement. In addition, this thesis adopts the concept of risk analysis and suggests an approach to evaluate the potential for traffic interruption, human life loss and property damage due to a rockfall occurrence.

碩士
國立交通大學
土木工程系
88
Based on the experience, the professional engineer provides the rating weights of the influenced parameters in the rockfall hazard rating systems. Therefore, the given rating weights will strongly depend on anybody’s subjective sense. One can obtain more conviction in the results of learning by using Artificial Neural Network (ANN). The network framework will be perfect by increasing of the learned cases. ANN is not alike traditional hazard rating system that will affect the function in using. The objects of this study are the areas along the Central Cross-Range Highway and the New Central Cross-Range Highway. The former area had been destroyed seriously and was temporarily closed due to 921 Chi-Chi Earthquake in 1999. The later area had been destroyed nearby 121.2k、136.8k、146.2k、147.7k. It presented the outstanding results of learning and rating for two areas through ANN. Furthermore, the another ANN model includes the geologic factors and two rainfall parameters will predict the hazard of raining for all slopes. Based on the ANN model, the rockfall hazard ranks can be determined following the weather forecast from the Central Weather Bureau. Also, the road manager should temporarily stop the road users to get into the area if it had been destroyed seriously.

Research Doctorate - Doctor of Philosophy (PhD)
Managing the rockfall hazard is a complex task, which involves several phases from land planning to the design of protective structures. Despite the increasing interest in rockfall-related research over the last few decades, some issues remain only partially addressed to date. In particular, existing predictive tools for the simulation of block trajectories could be improved and the criteria for the design of flexible metallic barriers are potentially flawed by block size effects. In the Australian context, the lack of research into rockfall phenomena has prevented the development of a comprehensive hazard characterisation so far; moreover, some types of barriers currently in use present cost-effectiveness issues. In this thesis, formed by six peer-reviewed publications, the aforementioned issues are investigated, with the aim of improving the knowledge regarding rockfall, especially for the Australian environment. The first paper presents the results of extensive in situ tests performed in different geological environments in NSW. Rockfall motion parameters are obtained for the first time in the Australian context and uncommonly high values of the normal coefficient of restitution are highlighted. An investigation of these results is undertaken in the second paper through extensive laboratory testing: low impacting angles, rotational energy and block shape are correlated to the high values of kn obtained in the experiments. In the third paper, the results from in situ tests are applied to real profiles taken from a database of Australian slopes: a basic hazard characterisation is performed using a 2D lumped mass model and low impact energy values are found for most of the cases. The fourth paper shows a comparison between four different flexible barriers, carried out by full-scale laboratory testing. The results provide an insight on the estimation of the barriers’ performance: in particular, stiffness and load transmission are evaluated, and modifications to improve the performance of one of the systems are suggested. Experimental and numerical evidence of the bullet effect are presented in the fifth and sixth papers. A Finite Element model of a mesh panel, calibrated by means of laboratory testing, is used to validate an innovative dimensional approach.

Dissertação de Mestrado em Geociências apresentada à Faculdade de Ciências e Tecnologia
Timor-Leste tem uma topografia aproximada e uma geologia complexa que contribuem para a ocorrência de um grande número de problemas de estabilidade de taludes, que são agravados pelas recentes atividades de construção de estradas visando melhorar as estradas antigas. O grande número de cortes, às vezes com uma alta considerável, é uma causa frequente de várias instabilizações que exigem um estudo detalhado. A área onde foi realizada a pesquisa de Análise de Estabilidade de Taludes (SSA) está localizada em Maubara, no município de Liquiça, ao longo da estrada de Karimbala, que liga os municípios de Liquiça e Bobonaro. Verificou-se a ocorrência de instabilizações de taludes sistematicamente ao longo dos anos, sendo as mais recentes ocorridas em Janeiro de 2018. Os objetivos gerais desta pesquisa foram estudar os problemas de estabilidade de encostas e calcular o Fator de Segurança (FoS). Para a caracterização do material da encosta e sua classificação geomecânica, foi mapeada a inclinação para definir os materiais aflorantes, as descontinuidades foram caracterizadas e a resistência da rocha avaliada pelo martelo de Schmidt. Com base nos dados coletados no campo, as classificações geomecânicas RMR e SMR foram aplicadas aos taludes. A avaliação das condições de estabilidade também foi feita usando o software Rocscience (RocTopple, Slide, RocFall) adequado para cada caso de instabilizações. As diretrizes de classificação do sistema Rockfall Hazard Rating System (RHRS) para avaliar cada ocorrência também foram utilizadas. Os tipos de roturas identificadas foram queda de rochas, basculamento, queda de detritos, rotura planar e rotura em cunha. Quedas de pedras e queda de detritos são freqüentes em todos os taludes de TzPt1 a TzPt6, em contraste com a rotura em cunha, que ocorre apenas em TzPt2 e TzPt6. As duas principais causas de instabilidade dos taludes são as descontinuidades geológicas com orientação desfavorável e as chuvas intensas que adicionam peso e induzem altas pressões de água nos terrenos das encostas, aumentando o potencial de ocorrência de instabilizações de taludes, em períodos de chuvas moderadas a fortes. Os valores de FoS que foram calculados abaixo de 1,5, foram considerados insuficientes para uma estabilidade de longo prazo. Os resultados de RHRS calculados são maiores que 300. Portanto, pode-se concluir que os taludes TzPt1 a TzPt6 são vulneráveis a roturas. A mitigação deve ser implementada com urgência para reduzir os danos na estrada e nos condutores. É altamente recomendável desenvolver um projeto técnico adequado das encostas considerando um FoS adequado para a estabilidade a longo prazo, usando técnicas de melhoria ajustadas às condições locais tais como: redução da altura do talude (redução das tensões), redução do ângulo de inclinação (redução das tensões de sobrecarga), melhoria da drenagem (redução da pressão da água dos poros), reforço do talude (aumento da resistência ao cisalhamento da superfície potential de deslizamento). Nalguns taludes que apresentavam condições de instabilidade foram simulados alguns procedimentos de estabilização de modo a avaliar as melhores soluções a serem utilizadas.
Timor-Leste has a rough topography and a complex geology contributing to the occurrence of a large number of slope stability problems, which are aggravated by recent road construction activities aiming to improve the old roads. A large number of cuts, sometimes with a considerable high are a frequent cause of several failures that require a detailed study. The study area where the research on Slope Stability Analysis (SSA) was done, is located in Maubara, in the Municipality of Liquiça, along the Karimbala road, which links the Liquiça and the Bobonaro Municipalities. It was verified that slope failures have occurred systematically throughout the years, the most recent ones occurred in January 2018. The general objectives of this research were to study the slope stability problems and to compute the Factor of Safety (FoS). For the characterization of the slope material and its geomechanical classification, the slope was mapped to define the outcropping materials, the discontinuities were characterized and the strength of the rock was evaluated using the Schmidt hammer. Based on the data collected in the field, the RMR and the SMR geomechanical classifications were applied to the slope. The evaluation of the stability conditions was also done using the Rocscience software (RocTopple, Slide, RocFall) suitable for each individual slope failure. The Rockfall Hazard Rating System (RHRS) classification guidelines to rate each occurrence was also used. The types of failures identified were rockfall, toppling, debris fall, plane failure and wedge failure. Rockfalls and debris fall are frequent on all slopes from TzPt1 to TzPt6, in contrast to the wedge failure, which only occurs in TzPt2 and TzPt6. The main causes of slope instability are the geological discontinuities with unfavorable orientation, the surface weathering and the intense rainfall which add weight and induce high water pressure in the slopes. The FoS values computed lower than 1.5, are considered as insufficient for a long-term stability. The RHRS results computed are greater than 300. Therefore, it can be concluded that slopes TzPt1 to TzPt6 are vulnerable to additional slope failures. Mitigation must be urgently implemented to reduce damages in the road and drivers. It is highly recommended to develop proper technical design of the slopes considering a FoS suitable for long-term stability, using improvement techniques adjusted to the local conditions such as: reduction of slope height (reduction of overburden stress), reduction of slope angle (reduction of overburden stress), drainage improvement (reduction of pore water pressure), reinforcement of slope (increase of shearing resistance of slip surface). In a few slopes presenting unstable conditions a few improvement stability procedures were simulated, in order to evaluate the best procedure to be used.

碩士
東南技術學院
防災科技研究所
96
The rock slope along Taiwan No.2 Seafront Highway－－ located in northern Taiwan is prone to be fragmentized due to earthquake, wind weathering, orogeny, and sea erosion, etc. Moreover, most part of the roadway is excavated on one-side slope which will incur rockfall under the above circumstances. Therefore, several sections of this highway are classified as high risk areas of rockfall. As a matter of fact, rockfall causes frequent casualties on these sections of roadway according to the past record. The thesis attempts to explore the hazard risk of a vehicle driving through one of the most hazardous sections of this highway through analyzing the characteristics of the traffic flow. First, the field data is collected according to an experiment design. The χ2 goodness-fit tests are then deployed to check platoon size and vehicle gap size against exponential distribution and Weibull distribution, respectively. Combined with the basic principle of car-following theory, the probability of head-tail collision due to inadequate gap among vehicles is analyzed. Finally, the current hazard mitigation measures for improving rockfall hazard are examined for reference.

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.