Landslides occur both onshore and offshore. However, little attention has been given to offshore landslides (submarine landslides). Submarine landslides have significant impacts and consequences on offshore and coastal facilities. The unique characteristics of submarine landslides include large mass movements and long travel distances at very gentle slopes. This thesis is concerned with developing centrifuge scaling laws for submarine landslide flows through the study of modelling submarine landslide flows in a mini-drum centrifuge. A series of tests are conducted at different gravity fields in order to understand the scaling laws involved in the simulation of submarine landslide flows. The model slope is instrumented with miniature sensors for measurements of pore pressures at different locations beneath the landslide flow. A series of digital cameras are used to capture the landslide flow in flight. Numerical studies are also carried out in order to compare the results obtained with the data from the centrifuge tests. The Depth Averaged Material Point Method (DAMPM) is used in the numerical simulations to deal with large deformation (such as the long runout of submarine landslide flows). Parametric studies are performed to investigate the validity of the developed centrifuge scaling laws under the initial and boundary conditions given in the centrifuge tests. Both the results from the centrifuge tests and numerical simulations appear to follow the proposed centrifuge scaling laws, which differ from the conventional centrifuge scaling laws. The results provide a better understanding of the centrifuge scaling laws that need to be adopted for centrifuge experiments involving submarine landslide flows, as well as giving an insight into the flow mechanism involved in submarine landslide flows.

京都大学 / 0048 / 新制・課程博士 / 博士(工学) / 甲第18226号 / 工博第3818号 / 新制||工||1585(附属図書館) / 31084 / 京都大学大学院工学研究科都市社会工学専攻 / (主査)教授 清野 純史, 教授 三村 衛, 准教授 古川 愛子 / 学位規則第4条第1項該当 / Doctor of Philosophy (Engineering) / Kyoto University / DFAM

京都大学 / 0048 / 新制・論文博士 / 博士(工学) / 乙第13173号 / 論工博第4164号 / 新制||工||1699(附属図書館) / (主査)教授 寶 馨, 教授 渦岡 良介, 准教授 佐山 敬洋 / 学位規則第4条第2項該当 / Doctor of Philosophy (Engineering) / Kyoto University / DFAM

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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.

No description available.

No description available.

Champlain Sea Clay (also known as Leda Clay) is a sensitive marine clay that was deposited within the limits of the Champlain Sea transgression during the final retreat of the Laurentide ice sheet. Upon isostatic rebound, the watersheds incised deep river valleys throughout the Ottawa region. These sensitive clay river banks have been shown to be highly susceptible to large retrogressive landslides. A cone penetration testing and hydrogeological program was developed in this thesis to characterize a retrogressive landslide along a creek valley consisting mainly of Champlain Sea Clay. As Champlain Sea Clay has been commonly shown to consist of banded layers, a 2 cm2 piezocone, and 5 cm2, 10 cm2 and 15 cm2 CPTu cones were used to demonstrate that the slightly larger 5 cm2 penetrometer was the most practical size for investigating landslides in Champlain Sea Clay. In doing so, the 5 cm2 cone was capable of high resolution stratigraphic profiling, locating remoulded layers for slip surface detection and characterizing the Champlain Sea Clay landslide near Ottawa. Due to the significant effects of the pore pressure distribution on slope stability and retrogressive behavior, a long term hydrogeological program was initiated which defined the ground water regime and real-time pore pressure data during a retrogressive landslide event. The seasonal change in the ground water regime from rapid snowmelt has shown to be a significant hydrogeological influence on triggering a retrogressive landslide along Mud Creek. With regular monitoring over multiple seasons, the seasonal pore pressure changes can be used to further understand the long term development of retrogressive landslides in Champlain Sea Clay. / Thesis (Master, Civil Engineering) -- Queen's University, 2013-09-27 14:13:40.196

Rainfall-induced landslides that change into debris flows and travel large distances are one of the treacherous natural calamities that can occur in mountainous areas, particularly in Nepal’s mountains. Debris flow was the second highest cause of human death in Nepal after epidemics between 1971 and 2016. Because debris flow is common in mountainous regions, its prediction and remedial measures through land use plans are important factors to consider for saving lives and properties. The spatial distribution of the initial landslides that change into debris flow, on a watershed scale, is still an important area of study in this mountainous region to develop essential land use plan. In this research, hydrologic, slope stability and Flow-R models are applied in GIS modeling to locate potential landslide and debris flow areas for a given threshold rainfall in a mountainous watershed-Kulekhani, Nepal. Soil samples from 73 locations within the watershed and a geotechnical investigation on one old landslide area were considered to determine the Soil Water Characteristics Curve (SWCC), friction angle, cohesion, and infiltration characteristics of the subsurface soils in the study area. This information is applied in an unsaturated slope stability model to find unstable locations in the study watershed in a GIS environment. The model is tested on a recorded 24-hour rainfall of 540 mm in the watershed, and potential landslide locations are obtained. The validation results show that there is a good agreement between the predicted and mapped landslides. For debris flow run out, Flow-R model, which has the capability to analyze debris flow inundation with limited input information, and the model software is readily available in the public domain, was chosen for further analysis. Two recent debris flow events and the study watershed are taken as case studies to identify the appropriate algorithms of Flow-R for runout analysis of the study areas. Landslide-triggering threshold rainfall frequency is related to the frequency of landslides and the debris flow hazard in these mountains. The above validated models are applied in a GIS environment to locate potential debris flow areas in expected threshold rainfall. Rainfall records from 1980 to 2013 are computed for one- to seven-day cumulative annual maximum rainfall. The probable rainfalls for 1 in 10 to 1 in 200 years return periods are identified. The anticipated probable rainfalls are modeled in the GIS environment to identify the factor of safety of mountain slopes for landslide susceptibility in the study watershed. The Flow-R model with user-defined landslide-susceptible areas was chosen for debris flow runout analysis. A relation between the frequency of rainfall and landslide-induced debris flow hazard area is derived for return periods of 25, 50, 100, and 200 years. Also, the debris flow hazard results from the analysis are compared with a known event in the watershed and found to agree. This developed method can be applied to anticipated landslide and landslide-induced debris flow from the live rainfall record to warn hazard-prone communities for saving lives and regulating hazardous transportation corridors in these mountains. In addition to this, this methodology will be a useful tool to help policy makers create appropriate land use plans.