The development of an interactive computer model for managing geologic hazards databases is vital and long overdue. As highway rockslopes continue to age and become more unstable and earthen dams are subjected to ever increasing flood events, a more proactive management system is required in order to provide timely information to planners and emergency personnel on demand. In recent years, deaths have occurred associated with both highway rockslides and earthen dam failures in southwest Virginia. In February 1991, a rockfall event occurred on Route U.S. 11 in the City of Radford, VA, which resulted indirectly in a highway accident and fatality. The incident made all parties aware that rockfalls from aging highway roadcuts within the city limits pose some threat to the motoring public (Watts et al., 1996). Additionally, in June 1995, the Timberlake dam in Lynchburg, VA, failed due to flash flooding from intense summer storms. Two people died on highways downstream of the dam, even though emergency personnel were on the scene. The lack of organized critical information about the dam, its downstream flood inundation zone, and its emergency action plan contributed to the tragedy. The outcome of the ensuing litigation is pending. In the case of the City of Radford, a user-friendly interactive database containing structural stereonet analysis, digital images, hazardous slope conditions, and maintenance records would provide a proactive approach to rockslope maintenance by allowing the slopes to be ranked in terms of geologic and traffic conditions. Appropriate remediation measures can then be taken in the most cost-effective manner. In the case of the Timberlake dam failure, a database containing critical information about the dam, its upstream watershed characteristics, downstream flood inundation zones, and emergency action plan could have been accessed by state geologists and emergency dispatchers. Appropriate measures could have been taken to deal with the event as it was unfolding. / Master of Science

Le travail présenté dans ce mémoire a porté sur l’auscultation d’un versant rocheux potentiellement instable, les Rochers de Valabres, soumis aux variations naturelles de température de surface. En effet, les variations thermiques sont supposées agir comme facteur préparatoire aux éboulements. Leur action est continu, lente et quasi-imperceptible mais le phénomène est peu exploré et rarement quantifié. Préalablement à l’auscultation, une phase de caractérisation du versant, basée sur des relevés topographiques par scannérisation laser, des mesures de contraintes et des essais en laboratoire, a été menée. Ces investigations ont permis d’appréhender les paramètres intrinsèques du versant et de mettre en évidence, dans la zone superficielle, un état de contraintes élevées, marqué par une forte rotation des axes principaux et influencé par la topographie et la présence d’hétérogénéités. L’auscultation des phénomènes thermomécaniques a été réalisée par un réseau de mesures de déformations et de températures en forage. Les mesures de température ont permis d'évaluer les apports de chaleur, en fonction du temps et de l’espace. Les mesures de déformations, bien qu’affectées par de nombreux artefacts instrumentaux, ont permis de quantifier le phénomène, à l’échelle quotidienne et annuelle, en terme de déformations, de contraintes équivalentes et de profondeurs d’influence. Afin d’explorer l’hypothèse de propagation de fissures sous contraintes d’origine thermique, une approche analytique, basée sur la mécanique de la rupture, a été mise en œuvre. Cette démarche a permis de révéler que les niveaux de contraintes / déformations mesurés sur le site étaient suffisants, sous certaines conditions et hypothèses, pour induire la propagation de fissures préexistantes. Par conséquent, les travaux menés dans cette thèse permettent de confirmer que les phénomènes thermomécaniques constituent un facteur préparatoire non négligeable aux éboulements et peuvent contribuer à la dégradation de la matrice rocheuse et/ou des ponts rocheux par propagation de fissures préexistantes / The present work focuses on the monitoring of a rockslope, prone to instability, named “Rochers de Valabres”, subjected to natural thermal fluctuation at the rock surface. Thermal variations are supposed to be a preparatory factor for rockfalls. Their action is continuous, slow and imperceptible. This phenomenum is not widly studied and seldom quantified. As a first step, investigations, based on topographic survey using Lidar, stress measurements and laboratory testing, have been performed. They reveals parameters of the rockslope, as well as the stress field at shallow depths, characterized by high magnitudes, high turnover of the principal orientations and affected by topography and geological heterogeneities. Thermomechanical monitoring was performed by a network composed of strain cells and thermal sensors, deployed in boreholes. Thermal data give us information about thermal transfer, as a function of time or space. Strain variation data, although affected by thermal artefacts, give quantitative information on strains, equivalent stresses and depth of influence, on daily and seasonal basis. In order to evaluate the assumption of fracture propagation on thermal loading, an analytical model, based on fracture mechanic, is suggested. Using specific conditions and assumptions, this model reveals that measured stress and strains are sufficient to lead to propagation of pre-existing discontinuities. Consequently, this study confirms that thermomechanical variations can be considered as a non negligible preparatory factor for rockfall and can contribute to mechanical degradation of the rock masse and discontinuities

The aim of this research was to study the relationship between rock slope stability and glacial processes. An in-depth analysis of our current understanding of how glaciated rock slopes develop instability and movement during deglaciation is presented; this shows that understanding is incomplete without an appreciation of the variable mechanical behaviour of glacier ice. In this thesis, I argue that: (1) The ductile behaviour of ice at low strain rates allows movement of rock slopes buttressed by ice. Field evidence and simple force models are used to explore rate of movement of ice-contact slopes and the conditions under which they evolve. The results indicate that large rockslides can move and deform glacial ice at rates of 10-2 to 102 m-yr. This implies that ice-contact slope movement may be important for slope evolution and the erosion and entrainment processes of glaciers; and (2) the elastic strength of glacier ice at the high strain rates associated with seismic shaking enables ice to modify the response of the surrounding rock to seismic shaking. To explore this, numerical analyses of the interaction between glacial erosion, glacier mass, topography, and earthquake shaking intensity are undertaken. Shaking of mountains of variable shape and with different levels of ice inundation is simulated using FLAC 6.0. The results suggest that complete inundation by ice can significantly reduce shaking intensity. This, in combination with glacial steepening of slopes, may make recently deglaciated slopes more prone to coseismic failure. In the final chapter of the thesis, I present a conceptual model of the evolution of slope stability during stages of glaciation and deglaciation. The model incorporates the ideas presented in the thesis. I then offer recommendations for how our understanding of these processes can be further advanced.

Tato diplomová práce se zabývá zhodnocením inženýrskogeologických poměrů mostu na stavbě č. 519 silničního okruhu kolem Prahy včetně vyšetření stability skalních svahů v místě předpokládané výstavby. Jedná se o přemostění hlubokého erozního údolí Vltavy, na jehož svazích vystupují na povrch horniny svrchnoproterozoického stáří. Na lokalitě byly zhodnoceny pomocí rešerše archivních podkladů, vlastní rekognoskace a laboratorních zkoušek, geologické, hydrogeologické a inženýrskogeologické poměry, které jsou přehledně uvedeny v inženýrskogeologické mapě v měřítku 1:2000 a řezu 1:500. Jako podklad pro vyhodnocení stability skalních svahů sloužila podrobná dokumentace skalních výchozů. Samotné vyšetření stability proběhlo pomocí klasifikace Slope Mass Ratting a Marklandova testu pro stereografickou projekci. Na výstupech práce je souhrnně popsán horninový masiv včetně mapy stability skalních svahů v měřítku 1:500 a popsány základové poměry uvažovaného mostu.