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Landslides in sensitive clays represent a severe geohazard in eastern Canada and Scandinavia. Triggered by various factors, such as toe erosion, earthquake, and human activities, a sensitive clay landslide can affect a large area and cause damage to infrastructure. The evaluation of risk associated with sensitive clay landslides is an important but challenging task because the failure mechanisms are not well understood. Different types of landslide (e.g. flowslide, monolithic slide, and spread) occur through significantly different failure processes that affect both retrogression and run-out. Full-scale modeling of such large-scale landslides is not practically feasible. On the other hand, real-time monitoring of the failure in the field is not possible. Therefore, the characteristics of the landslides are generally evaluated by comparing post-slide field investigations with available information on the site before the landslide. Numerical modeling could be an alternative tool to obtain further insights into the failure mechanisms. The failure occurs by progressive formation of shear bands where extremely large plastic shear strain generates, and the failed soil displaces over a large distance. Consequently, the methods commonly used for slope stability analysis, such as limit equilibrium (LE) methods and Lagrangian-based finite element (FE) methods, cannot be used to model the whole process of a sensitive clay landslide. The main objective of the present study is to analyze the factors affecting the failure pattern and extent of sensitive clay landslides triggered by toe erosion and seismic loading. A large deformation finite element (LDFE) method based on Eulerian approach is used to simulate the triggering of the landslide, subsequent failure of soil blocks and run-out of the debris. The landslide generally occurs rapidly in a matter of few minutes; therefore, the simulation is performed for the undrained condition. The strain-softening behavior of sensitive clay is defined as a function of plastic shear displacement that reduces the undrained shear strength to a very low value at a large strain. A strain-rate dependent undrained shear strength model is used, which can model the behavior of soil and remolded clay that flows at a high speed as a fluid-like material. The formation of a slope generally occurs due to the removal of the materials in drained condition. Moreover, groundwater seepage might dominate the failure of a slope. Numerical simulation techniques for the Eulerian based LDFE method are developed to simulate in-situ effective stresses, which can be used for the cases of widely varying earth pressure coefficient at rest, even greater than unity. Based on the thermal-hydraulic analogy, a numerical modeling technique is developed for seepage analysis. The above-mentioned methods can successfully simulate the initial stress condition in the soil that affects the failure mechanisms significantly. Many failures of sensitive clay slope are initiated by toe erosion. Conducting LDFE simulations, the potential conditions required for a flowslide and a spread are identified. The type and extent (retrogression and run-out) of a landslide depend on a combination of several factors related to geometry and soil properties. A single parameter, such as stability number, remolded shear strength, liquidity index or remolded energy, may not always be suitable to categorize failure type. Increasing lateral earth pressure coefficient at-rest shows a trend of occurring spreads, while a low remolded shear strength and favorable conditions for rapid displacement of debris result in flowslides. The comparison of LDFE simulations and post-slide investigations of the 2010 Saint-Jude landslide show that the present numerical simulations can explain several features of the landslide, including the effects of seepage and an opposite riverbank on progressive failure. Finally, pseudostatic and dynamic analyses are performed using the developed LDFE method to study the progressive formation of failure planes in clay slopes subjected to earthquake loading. The LDFE modeling in Eulerian approach can simulate the large displacement of the failed soil blocks, considering the reduction of shear strength due to strain-softening.
Earthquake induced landslides pose a significant threat to many communities, environment and infrastructure. The potential damages could be severe in sensitive clay slope failures because the post-peak softening behaviour could cause retrogressive failure of soil blocks resulting in large-scale landslides. The failed soil blocks generally displace over a large distance during earthquake and post-quake stages. Therefore, upslope retrogression and downslope runout are two important phenomena need to be studied for better understanding of risks associated with landslides in sensitive clays. The traditional limit equilibrium methods, commonly used in slope stability analysis, cannot model retrogressive failure or deformation of slopes. The present study concentrates on development of large deformation finite element (FE) models using a Coupled Eulerian- Lagrangian (CEL) approach to simulate the failure of soft and sensitive clay slopes triggered by earthquakes. Analyses are performed for pseudostatic and dynamic loading conditions modeling the undrained behaviour of clay as elasto-plastic material with and without post-peak degradation of shear strength. A nonlinear post-peak strength degradation model as a function of accumulated plastic shear strain is implemented in FE analysis. In addition to CEL, FE analyses are performed using Lagrangian-based FE techniques to show the advantages of CEL to simulate large landslides. The CEL approach can successfully simulate the formation of shear bands (zone of accumulated shear strains), type of failure commonly observed after earthquake, upslope retrogression and downslope runout for varying geometry and soil properties.
Landslides in sensitive clays represent a major hazard in the northern countries of the world such as Canada, Finland, Norway, Russia, Sweden and in the US state of Alaska. Past and recent examples of catastrophic landslides at e.g. Saint-Jean-Vianney in 1971, Rissa in 1979, Finneidfjord in 1996 and Kattmarka in 2009 have illustrated the great mobility of the remolded sensitive clays and their hazardous retrogressive potential. These events call for a better understanding of landslide in sensitive clay terrain to assist authorities with state-of-the-art hazard assessment methods, risk management schemes, mitigation measures and planning. During the last decades the elevated awareness regarding slope movement in sensitive clays has led to major advances in mapping techniques and development of highly sophisticated geotechnical and geophysical investigation tools. Great advances in numerical techniques dealing with progressive failure and landslide kinematic have also lead to increase understanding and predictability of landslides in sensitive clays and their consequences. This volume consists of the latest scientific research by international experts dealing with geological, geotechnical and geophysical aspects of slope failure in sensitive clays and focuses on understanding the full spectrum of challenges presented by landslides in such brittle materials.
This book gathers the most recent scientific research on the geological, geotechnical and geophysical aspects of slope failure in sensitive clays. Gathering contributions by international experts, it focuses on understanding the complete and practical spectrum of challenges presented by landslides in such complex materials. Based on sound and validated research results, the book also presents several recommendations that could be implemented in the guidelines or code-of-practice. These recommendations cover topics including the characterization and behavior of sensitive clays; the pre-failure, failure and post-failure stages of sensitive clays; mapping and identification methods; climate change; hazard assessment; and risk management. Sensitive clays are known for their potential for causing large landslides, which pose a serious risk to human lives, infrastructure, and surrounding ecosystems within their reach. This has been demonstrated by the recent catastrophic landslides in e.g. Sørum (2016), Skjeggestad (2015), Statland (2014), Byneset (2012), St-Jude (2010), Lyngen (2010) and Kattmarka (2009). The 2015 collapse of the Skjeggestad Bridge in Norway – which was due to a landslide in sensitive clay – alone costs millions of dollars in repairs. Recently, efforts are being made to increase society’s ability to cope with such landslide hazards. Geoscientists are now expected to provide input to the agencies responsible for landslide-risk preparedness. In other words, geoscientists’ role is not only to act as technologists to establish new theories, but also to go the extra mile to implement them in practice, so as to find meaningful solutions to geotechnical problems.
Amongst the thematic topics discussed are global frequency, impacts on society, analysis of initial rock slope failure, monitoring of rock slope movement, analysis and modeling of post-failure behaviour, volcanic landslides, and influences of massive rock slope failure on the geomorphological evolution of mountain regions. Regional contributions include reports on rockslides and rock avalanches in Norway, western Canada, the Andes of Argentina, the Karakoram Himalaya, the European Alps, the Appennines, and the mountains of Central Asia. Rockslides and rock avalanches in the Central Asian republics of the former Soviet Union are discussed in detail for the first time in an English-language book. These landslides include the 1911 Usoi rockslide, that dammed 75 km-long Lake Sarez, and the 1949 Khait rock avalanche that may have killed up to 28,000 people. Both landslides were earthquake-triggered and both are located in Tajikistan. An additional highlight is a detailed description and analysis of large-scale artificial rock avalanches triggered by underground nuclear explosions during the testing programme of the former Soviet Union.
This book sheds new light on improved methods for the study of the initiation and run-out of earthquake-induced landslides. It includes an initiation study method that considers tension-shear failure mechanism; an improved, rigorous, dynamic sliding-block method based on dynamic critical acceleration; and a run-out analysis of earthquake-induced landslides that takes account of the trampoline effect, all of which add to the accuracy and accessibility of landslide study. The book includes abundant illustrations, figures and tables, making it a valuable resource for those looking for practical landslide research tools.
Landslides and Engineered Slopes. Experience, Theory and Practice contains the invited lectures and all papers presented at the 12th International Symposium on Landslides, (Naples, Italy, 12-19 June 2016). The book aims to emphasize the relationship between landslides and other natural hazards. Hence, three of the main sessions focus on Volcanic-induced landslides, Earthquake-induced landslides and Weather-induced landslides respectively, while the fourth main session deals with Human-induced landslides. Some papers presented in a special session devoted to "Subareal and submarine landslide processes and hazard” and in a “Young Session” complete the books. Landslides and Engineered Slopes. Experience, Theory and Practice underlines the importance of the classic approach of modern science, which moves from experience to theory, as the basic instrument to study landslides. Experience is the key to understand the natural phenomena focusing on all the factors that play a major role. Theory is the instrument to manage the data provided by experience following a mathematical approach; this allows not only to clarify the nature and the deep causes of phenomena but mostly, to predict future and, if required, manage similar events. Practical benefits from the results of theory to protect people and man-made works. Landslides and Engineered Slopes. Experience, Theory and Practice is useful to scientists and practitioners working in the areas of rock and soil mechanics, geotechnical engineering, engineering geology and geology.
Most landslides are triggered by rainfall. In previous studies, slope stability is often evaluated based on the infiltration analysis. Hydro-mechanical coupling is significant to rainfall-caused landslide evolution. This book covers theoretical models of unsaturated infiltration, and provides hydro-mechanical models for rainfall-induced landslides. The influences of rainfall patterns, boundary conditions, layered structures, and SWCC hysteresis on the coupled unsaturated infiltration and deformation are discussed. Laboratory testing of rainfall-induced landslides is performed to study the developing process of landslide upon rainfall infiltration. The results provide a better understanding of rainfall-induced landslides.
Large earthquakes commonly trigger widespread and destructive landsliding. However, current approaches to modeling regional-scale landslide activity do not account for the temporal evolution of progressive failure in brittle hillslope materials. Progressive failure allows hillslopes to possess a memory of previous earthquakes, which has the potential to influence landslide activity in future earthquakes. The original contribution of this thesis is to address the influence of hillslope memory on spatial and temporal patterns of earthquake-triggered landslide activity, through a combination of landslide inventory analysis and numerical modeling. An understanding of spatial distributions of earthquake-triggered landslides is first established, through analysis of inventories of landslides triggered by five large (M_w > 6.7) earthquakes. The results show how current landscape conditions at the time of earthquakes influence hillslope failure probability. By identifying factors exhibiting a common influence on landslides triggered by all five earthquakes, general spatial models of landslide probability are developed, which are transferrable between different earthquakes and regions. Analysis of model performance for landslide distributions triggered by two sequential earthquakes is then used to establish where this spatial approach breaks down. Errors in the landslide distribution predicted for the second earthquake suggest that the legacy of damage to hillslope materials accrued from the first earthquake is an important control on landslide occurrence. Given the infrequent recurrence of large earthquakes and limited temporal coverage of landslide data, a new modelling approach is developed to understand how hillslope memory influences long-term patterns of earthquake-triggered landslide activity. The model integrates the site-scale evolution of hillslope progressive failure into modeling regional-scale earthquake-triggered landslide activity, in response to sequences of earthquakes. The model results suggest that the sensitivity of landscapes to landslide-triggering increases following large earthquakes, due to damage accumulated in hillslopes that do not reach the point of failure, and decays as these hillslopes fail in response to subsequent, lower-magnitude events. Prolonged elevated levels of rainfall-triggered landslide activity observed following large earthquakes appear to reflect this result. Using the model outputs, a methodology is proposed for predicting temporal variability in landslide activity using records of seismic data. The model results also suggest that, when hillslopes undergo progressive failure, relationships between seismic forcing and landslides are influenced by the magnitude-frequency distribution of earthquakes. As a result, current approaches that use these relationships to predict levels of long-term landslide hazard and erosion rates, but do not account for regional differences in earthquake distributions, may suffer from systematic under- or over-prediction. These significant implications for predicting the geomorphological and human impact of landslides highlight the need for detailed multi-temporal datasets recording the evolution of landslide activity following major earthquakes, in order to quantitatively investigate the influence of hillslope memory in real landscape settings.
270 Expert contributions on aspects of landslide hazards, encompassing geological modeling and soil and rock mechanics, landslide processes, causes and effects, and damage avoidance and limitation strategies. Reference source for academics and professionals in geo-mechanical and geo-technical engineering, and others involved with research, des