The Saint Lawrence Lowlands in eastern Canada contain extensive deposits of marine soils deposited in post-glacial seas during and following the retreat of the most recent continental glacier. These marine soils include silt and clay deposits known collectively as Champlain clay. When the pore fluid in these marine deposits has changed over time to a lower salinity, the clay can become very sensitive, or demonstrate substantial strength loss after reaching the peak strength with sufficient strain under undrained load conditions. Sensitive clay soils are subject to a peculiar type of very large landslide that typically involves great extents of nearly horizontal ground, usually occurring suddenly and without warning. These landslides tend to be described as “retrogressive” in the literature and practice, implying that they develop as a series of successive small failures that advance rearward until a final stable position is reached. The work of this thesis is organized into four different themes, with an overall objective of understanding the hazard and risk associated with large landslides in sensitive clay to linear infrastructure such as railways. The first theme, documented in Chapter 2, develops a number of spatial relationships between specific physiographic and geologic features and landslide occurrence or absence, as determined through air photo analysis and a review of the literature. The second theme, documented in Chapter 3, presents the construction of a digital database of large landslides in sensitive clay in eastern Canada, for the purposes of studying landslide susceptibility, hazard and risk. The third theme, documented in Chapters 4 and 5, presents and defends a novel mechanical model for development of these large landslides. This model suggests the landslides develop progressively, rather than retrogressively, and the science of fracture mechanics is employed to substantiate the model. The fourth theme, documented in Chapters 6 and 7, synthesizes the findings of the earlier themes and presents a methodology for estimating landslide susceptibility in Champlain clay. That approach is then extended to develop an understanding of the hazard. The concluding chapter extends that work to present an initial appreciation of landslide risk to railways. / Thesis (Ph.D, Geological Sciences & Geological Engineering) -- Queen's University, 2009-04-23 13:22:19.53

This thesis has examined the 30km long rail corridor through the Lower Buller Gorge, on the Stillwater Ngakawau Line, between SNL96 and 126km, using a landslide risk management approach. The project area is characterised by high annual rainfall (>2,000mm per year), and steep topography (slopes typically ≥20°) adjacent to the rail corridor. The track formation generally follows the natural contour near the base of the hillslope through the Lower Buller Gorge, and consequently involves many curves but relatively limited cut slopes into adjacent rock outcrops. The distance between the base of adjacent hillslopes and rail is frequently <2m horizontally. A variety of basement and Tertiary lithologies are present, including granite, breccias, indurated sandstone/mudstone, and limestone. The primary focus of this thesis has been on upslope-sourced landsliding onto the rail corridor, and on two short lengths (20m and 450m) that currently have a 25km/hour speed restriction imposed at Whitecliffs and Te Kuha respectively. Rainfall-induced and earthquake-generated landslide triggering mechanisms were examined in detail. A landslide inventory has been compiled to determine the characteristics and distribution of identified slope failures over time, and to establish any correlation with topography and geology. Sixty individual landslide events were identified since the line became fully operational in the 1940s, based on desktop reviews, and field inspections for more recent events. To reflect the presence of small magnitude landslide events, a project-specific logarithmic classification of landslides was adopted from <10m³ (very small volume) to ≥10,000m³ (very large volume). An absence of a higher proportion of ‘very small’ to ‘small’ landslide volumes (<100m³) in the inventory reflects incomplete reporting of these comparatively lower magnitude, but higher frequency, events. The establishment of a robust landslide inventory to document future events, in a consistent and readily accessible format, is required for continued monitoring and review of landslide risk management practices in the Lower Buller Gorge. Combining landslide inventory data and physical characteristics of the project area enabled the development of a qualitative landslide zonation map that assigned ‘high’, ‘high-moderate’, ‘moderate’ and ‘low’ landslide susceptibility classes. The principal area of slope instability above the rail corridor is 22.5km in length between SNL103.5 and 126.0km, associated predominantly with basement lithologies (Tuhua Granite; Hawks Crag Breccia; Greenland Group). The most frequently occurring landslides are shallow, typically less than 3m deep, translational failures triggered in regolith or colluvium materials. Rainfall-induced debris slides and flows are dominant, given the high annual rainfall and associated high frequency of high intensity or long duration rainfall events. Very small to medium landslides (<1,000m³) have the potential to impact the rail corridor with an average frequency of around one every two years, causing damage to infrastructure or affecting rail operations. Very large landslides (≥10,000m³) can be expected every 10 to 20 years based on a limited historical record. The narrow rail corridor and absence of sufficient catch areas above or adjacent to the rail causes continual operational challenges due to upslope-sourced landslide debris, and high susceptibility to slope failures, particularly west of SNL103.50km. Development of a rainfall-threshold for proactive inspection of the rail corridor is recommended, including the establishment of a rain gauge network through the Lower Buller Gorge. Earthquake-generated landslides significantly impacted the rail during the magnitude 7.1 Inangahua earthquake in 1968 and to a much lesser extent during the magnitude 6.1 Westport earthquake in 1991. The rail was not fully constructed through the Lower Buller Gorge at the time of the magnitude 7.8 Buller (Murchison) Earthquake in 1929, which generated widespread landsliding in the Buller and Nelson regions. Earthquake-generated landsliding can be expected through the Lower Buller Gorge from earthquakes of magnitude ≥6, and track inspection is recommended in the event of magnitude 5 or greater earthquakes. Detailed geological characterisation and mapping at Whitecliffs and Te Kuha was conducted, including a LiDAR survey at Whitecliffs that enabled visualisation of the ground surface without the interference of vegetation. The limestone outcrop at Whitecliffs comprises 60-70m high near-vertical cliffs with a well-established talus apron at the base, extending to the rail corridor. Three widely spaced open fractures sets are present at the top of Whitecliffs that propagate into the cliff-face. There has been no detectable movement on selected key fracture sets since monitoring commenced in 1993 and there is no confirmed evidence of large-scale cliff collapse during the 1968 Inangahua earthquake. Whitecliffs is not as susceptible to failure as other slopes inspected in the project area due to structural controls, primarily being the dipping of strata back into the cliff-face and widely space joint sets. Establishment of inspection protocols for earthquake events impacting the area, including real-time monitoring of selected fractures at Whitecliffs is recommended. A 2km-length corridor site model produced for Te Kuha demonstrated ‘high’ landslide susceptibility is not confined to slopes above the existing 450m speed restriction zone. Removal of the speed restrictions at Whitecliffs and Te Kuha can be considered, as the increased exposure time is not considered sufficient justification given the extent of other susceptible areas to landsliding affecting the Lower Buller Gorge rail corridor. The principal conclusion from this thesis project is that there is on-going risk to rail operations predominantly from shallow translational landsliding in regolith-colluvium materials. The majority of these will be generated by long-duration or intense rainfall events. Development of threshold-based methods for effective track management is recommended, including the establishment of a rain gauge network through the Lower Buller Gorge, and landslide inventory database. Site-specific engineering measures could be adopted, such as catch benches or avalanche-type shelters, where justified on a cost-benefit basis.

Regional landslide risk, as it is most commonly defined, is a product of the following: hazard, vulnerability and exposed population. The first objective of this research project is to estimate the regional landslide hazard level by calculating its probability of slope failure based on maximum slope angles, as estimated using data provided by digital elevation models (DEM). Furthermore, it addresses the impact of DEM resolution on perceived slope angles, using local averaging theory, by comparing the results predicted from DEM datasets of differing resolutions. Although the likelihood that a landslide will occur can be predicted with a hazard assessment model, the extent of the damage inflicted upon a region is a function of vulnerability. This introduces the second objective of this research project: vulnerability assessment. The third and final objective concerns the impact of urbanization and population growth on landslide risk levels.

Neste trabalho foram integrados o mapeamento geológico de campo, os dados regionais aerogeofísicos e as imagens orbitais de alta resolução (1 m) para fornecer um mapa geológico detalhado do Pluton granítico Conselheiro Paulino, na Faixa Ribeira, Brasil. A área estudada possui poucos afloramentos e outras questões que dificultam o mapeamento geológico tradicional. Escorregamentos de terra são comuns na porção mais intemperizada do granito. A utilização de imagens orbitais de alta resolução permitiu a identificação dos poucos afloramentos existentes, além de outros elementos, como ravinas, planícies aluviais, eluviões, vegetação e estradas. Isso foi importante para orientar e otimizar as pesquisas de campo. A disponibilidade de dados aerogeofísicos magnéticos e radiométricos corroboraram nos trabalhos de campo e na petrografia do Pluton granítico Conselheiro Paulino. O pluton pode ser dividido em duas facies distintas, sendo uma de composição microgranítica e outra de composição microgranodiorítica / In the present work, we integrate field geological mapping, regional airborne geophysical data and high resolution (1 m) satellite images to provide a detailed geological map of the Conselheiro Paulino granitic pluton in the Ribeira Belt, Brazil. The studied area has few outcrops and other issues that limit the traditional geological mapping. Landslides are common in the highly weathered portion of the granite. The use of high-resolution images allowed the identification of the few available outcrops and other elements such as ravines, aluvial plains, eluvial deposits, vegetation and roads. This was important to guide and optimize the fieldwork surveys. The available magnetic and radiometric airborne geophysical data corroborate field and petrographic data about the Conselheiro Paulino granite pluton. The pluton can be divided into two distinct facies, one with microgranitic and the other with microgranodioritic composition.

Neste trabalho foram integrados o mapeamento geológico de campo, os dados regionais aerogeofísicos e as imagens orbitais de alta resolução (1 m) para fornecer um mapa geológico detalhado do Pluton granítico Conselheiro Paulino, na Faixa Ribeira, Brasil. A área estudada possui poucos afloramentos e outras questões que dificultam o mapeamento geológico tradicional. Escorregamentos de terra são comuns na porção mais intemperizada do granito. A utilização de imagens orbitais de alta resolução permitiu a identificação dos poucos afloramentos existentes, além de outros elementos, como ravinas, planícies aluviais, eluviões, vegetação e estradas. Isso foi importante para orientar e otimizar as pesquisas de campo. A disponibilidade de dados aerogeofísicos magnéticos e radiométricos corroboraram nos trabalhos de campo e na petrografia do Pluton granítico Conselheiro Paulino. O pluton pode ser dividido em duas facies distintas, sendo uma de composição microgranítica e outra de composição microgranodiorítica / In the present work, we integrate field geological mapping, regional airborne geophysical data and high resolution (1 m) satellite images to provide a detailed geological map of the Conselheiro Paulino granitic pluton in the Ribeira Belt, Brazil. The studied area has few outcrops and other issues that limit the traditional geological mapping. Landslides are common in the highly weathered portion of the granite. The use of high-resolution images allowed the identification of the few available outcrops and other elements such as ravines, aluvial plains, eluvial deposits, vegetation and roads. This was important to guide and optimize the fieldwork surveys. The available magnetic and radiometric airborne geophysical data corroborate field and petrographic data about the Conselheiro Paulino granite pluton. The pluton can be divided into two distinct facies, one with microgranitic and the other with microgranodioritic composition.

Se presenta un procedimiento para evaluar de forma cuantitativa el riesgo por deslizamientos teniendo en cuenta la peligrosidad, los elementos expuestos y su vulnerabilidad. El método utiliza los modelos de susceptibilidad obtenidos previamente a partir de las relaciones estadísticas existentes entre los deslizamientos ocurridos en el pasado (últimos 50 años) y una serie de parámetros del terreno relacionados con la inestabilidad. La frecuencia de deslizamientos en el pasado se ha utilizado para estimar frecuencias futuras. También se ha realizado un inventario y cartografía de los elementos afectados por deslizamientos en el pasado, y se han estimado los daños para cada tipo de elemento teniendo en cuenta la magnitud del tipo de deslizamiento analizado. Posteriormente se estimó la vulnerabilidad, que se expresa en valores de 0 a 1, a partir de la comparación entre pérdidas y valor del elemento afectado.La integración de la peligrosidad, vulnerabilidad y valor del elemento ha permitido obtener modelos de riesgo directo por deslizamiento para cada tipo de elemento. Además se han analizado las pérdidas indirectas ocasionadas sobre las actividades económicas por este proceso. El resultado final es un mapa de riesgo donde cada píxel muestra las pérdidas esperables por deslizamientos en los próximos 50 años / A quantitative procedure for landslide risk mapping has been developed considering hazard, vulnerability and exposed elements. The method is based on a susceptibility model previously developed from statistical relationships between past landslides occurred in the study area (last 50 years) and terrain parameters related to instability. Past landslide behaviour has been used to calculate landslide frequency for the future. An inventory of direct damage due to landslides during the study period was carried out and the main elements at risk in the area identified and mapped. Past monetary losses per type of element have been estimated and expressed as an average 'specific loss' for events of a given magnitude (corresponding to a specified scenario). Vulnerability has been assessed by comparing losses with the actual value of the elements affected and expressed as a fraction of that value (0-1).By integrating hazard, vulnerability and monetary value, direct landslide risk ( /pixel) has been computed for each element considered. Indirect losses from the disruption of economic activities due to landsliding have also been assessed. The final result is a risk map combining all losses per pixel for a 50-year period.