1,720,952 research outputs found
Infiltration-induced Slope Instability: a multi-scale approach
Full text linkPrecipitation, together with erosion and earthquakes, have been recognized as the main triggering factors of shallow landslides. However, there are relatively few well-documented cases where direct relationships could be established between occurrence and features of shallow landslides, the rainfall characteristics (e.g. intensity, duration) and water retention curves. A field experiment has been performed on a steep forested slope located on the east-facing banks of the river Rhine in Ruedlingen, northern Switzerland. The aim of the experiments was to study the triggering mechanisms of the landslides induced by rainfall. The pore pressure and the degree of saturation, which are linked through the water retention curve, represent two of the main variables affecting the mechanical behaviour of unsaturated soils, and their relationships to rainfall are complex. The difference in the determination of water retention curves at different scales are analysed in this paper for Ruedlingen soil together with their effects on mechanical behaviour at multi-scale
Simulation of debris flow on an instrumented test slope using an updated Lagrangian continuum particle method
No full textWe present an updated Lagrangian continuum particle method based on smoothed particle hydrodynamics (SPH) for simulating debris flow on an instrumented test slope. The site is a deforested area near the village of Ruedlingen, a community in the canton of Schaffhausen in Switzerland. Artificial rainfall experiments were conducted on the slope that led to failure of the sediment in the form of a debris flow. We develop a 3D mechanistic model for this test slope and conduct numerical simulations of the flow kinematics using an SPH formulation that captures large deformation, material nonlinearity, and the complex post-failure movement of the sediment. Two main simulations explore the impact of changes in the mechanical properties of the sediment on the ensuing kinematics of the flow. The first simulation models the sediment as a granular homogeneous material, while the second simulation models the sediment as a heterogeneous material with spatially varying cohesion. The variable cohesion is meant to represent the effects of root reinforcement from vegetation. By comparing the numerical solutions with the observed failure surfaces and final free-surface geometries of the debris deposit, as well as with the observed flow velocity, flow duration, and hot spots of strain concentration, we provide insights into the accuracy and robustness of the SPH framework for modeling debris flows.Accepted Author ManuscriptGeo-engineerin
Numerical modelling of slope–vegetation–atmosphere interaction: an overview
Full text linkThe behaviour of natural and artificial slopes is controlled by their thermo-hydro-mechanical conditions and by soil–vegetation–atmosphere interaction. Porewater pressure changes within a slope related to variable meteorological settings have been shown to be able to induce soil erosion, shrinkage–swelling and cracking, thus leading to an overall decrease of the available soil strength with depth and, ultimately, to a progressive slope collapse. In terms of numerical modelling, the stability analysis of partially saturated slopes is a complex problem and a wide range of approaches from simple limit equilibrium solutions to advanced numerical analyses have been proposed in the literature. The more advanced approaches, although more rigorous, require input data such as the soil water retention curve and the hydraulic conductivity function, which are difficult to obtain in some cases. The quantification of the effects of future climate scenarios represents an additional challenge in forecasting slope–atmosphere interaction processes. This paper presents a review of real and ideal case histories regarding the numerical analysis of natural and artificial slopes subjected to different types of climatic perturbations. The limits and benefits of the different numerical approaches adopted are discussed and some general modelling recommendations are addressed
Investigation of the Mechanical Behaviour of the Interface between Soil and Reinforcement, via Experimental and Numerical Modelling
No full textAbstractThe purpose of this study is to investigate the interface properties between soil and reinforcement, via experimental and numerical modelling of reinforced slopes. In particular, several scale models were built and tested under enhanced gravity in the geotechnical drum centrifuge at ETH Zurich and corresponding prototype numerical models were analyzed via a finite element stress analysis code. Optical fibre sensors were attached on the reinforcement layers of the experimental scaled models in order to measure linear strain during the increase of the g-level, and the results were compared to linear strain that was derived by the numerical analysis of the correspondent prototype reinforced slopes. The interface between soil and reinforcement was expressed in terms of normal and shear stiffness on the soil-reinforcement boundary and different values were tested in order to achieve validation of the experimental and numerical results
A novel technique to monitor the subsurface movements of landslides
Full text linkSlope Deformation Sensors SDS) were developed to monitor profiles of soil deformation at a high frequency during slope monitoring and landslide triggering experiments. It was hypothesised that the surface and subsurface movements could be combined to integrate the temporal development of the movements, and help to monitor the initiation and propagation of the shear bands indirectly, as well as to predict the volume of the eventual landslide. Four SDSs were installed in a 38ยบ slope in Northern Switzerland and slope movements due to two artificial rainfall sprinkling experiments in October 2008 and March 2009 were monitored. This paper describes the design, numerical validation, installation details and performance of the SDSs during the first rainfall event. The data acquired from SDS in terms of bending strain, deformation profiles, and an indication of the mechanical energy transmitted from the surrounding soil, are analysed and compared to the patterns of surface movements of the slope and changes in the horizontal earth pressure. The findings are interpreted based on the applied rainfall, hydrological properties of the slope, bedrock shape and the specifications of the observed failure surface in the following Landslide Triggering Experiment. Details of the data acquired from SDSs during the second experiment in March 2009 are reported and analysed in a second paper.The accepted manuscript in pdf format is listed with the files at the bottom of this page. The presentation of the authors' names and (or) special characters in the title of the manuscript may differ slightly between what is listed on this page and what is listed in the pdf file of the accepted manuscript; that in the pdf file of the accepted manuscript is what was submitted by the author
Controlled water-level system for breach analysis of levees within an enhanced acceleration field
No full textCorrect scaling of breach analysis of river levees is a challenging task that is not easily accomplished by physical modelling. Several small-scale physical model tests have been conducted at 1-g level, which cannot truly represent the stress-dependency of soils, whereas the scaling issues arising from centrifuge modelling have not been fully explored.Two key features have to be considered when modelling the prototype behaviour. On the one hand, the whole embankment should be included in the model to ensure that flow nets are valid. This is not always easy to achieve due to space limitations within the strongboxes used. On the other hand, full control of water levels, prior and during breaching, is of principal interest.This contribution shows how both of these features can be modelled for levee breaching by taking advantage of the availability of space within a drum centrifuge and its versatile toolplate
Triaxial stress path tests on artificially prepared analogue alpine permafrost soil
Full text linkSome degrading rock glaciers have been exhibiting deepening depressions, accelerating strain rates and, in some rare cases, sudden release of mass movements. Warming permafrost already mobilises lower strength as temperatures rise, however unusual stress paths with lateral stresses greater than vertical stresses, instead of vice versa, could exacerbate this with lower strength at failure, and hence higher vulnerability. This paper investigates the mechanical behaviour of artificially frozen soil specimens at temperatures between -3.0 and -0.3°C under various stress paths, axial (A) and lateral (L), compression (C) and extension (E), for total stress paths AC, AE, LE, LC. Acoustic emissions were detected during shearing in order to expose how the deformation mechanisms develop from a microstructural point of view. Deviatoric stress mobilised in the stress path tests was linearly dependent on the temperature (within the ranges tested): a temperature increase resulted in a decrease in residual deviatoric stress. Comparison between the residual deviatoric stresses obtained from the different stress path tests indicates that 1) values mobilised with radial stress greater than axial stress were lower than vice versa, 2) more strength was mobilised when changing lateral stress paths than axial, with 3) the lowest strength mobilised in AE beneath a depression.The accepted manuscript in pdf format is listed with the files at the bottom of this page. The presentation of the authors' names and (or) special characters in the title of the manuscript may differ slightly between what is listed on this page and what is listed in the pdf file of the accepted manuscript; that in the pdf file of the accepted manuscript is what was submitted by the author
Photogrammetric monitoring of an artificially generated shallow landslide
No full textAn artificial rainfall event was applied to a forested slope in Ruedlingen, northern Switzerland. The experiment triggered a landslide which resulted in mobilising about 130m3 of debris. The event was monitored by a photogrammetric network of four cameras, operating at 5 to 8 frames per second, in order to quantify spatial and temporal changes by tracking tennis balls pegged into the ground. Image measurements were performed using automated image matching methods, implemented through a software package developed in-house. Three-dimensional coordinates of the target points were estimated by running a customised type of bundle adjustment, achieving a positioning precision of +/- 1 center dot 8cm.This research was funded by the Competence Centre for Environment and Sustainability (CCES) within the framework of the TRAMM project. Amin Askarinejad, Professor Dr Sarah M. Springman, Marco Sperl, Stefan Moser, Ernst Bleiker, Felix Wietlisbach and Peter Kienzler kindly contributed to the work. The author is grateful to the Gemeinde of Ruedlingen and their President, Mrs Katy Leutenegger, for giving permission to carry out this experiment on their land. The author gratefully thanks Professor Dr Armin Gruen for his help and valuable comments. The author also thanks the anonymous reviewers for their valuable criticism and suggestions that improved the quality of the paperPublisher's VersionAuthor Post Prin
Precursors of instability in a natural slope due to rainfall: a full-scale experiment
No full textA full-scale landslide-triggering experiment was conducted on a natural sandy slope subjected to an artificial rainfall event, which resulted in mobilisation of 130 m3 of soil mass. Novel slope deformation sensors (SDSs) were applied to monitor the subsurface pre-failure movements and the precursors of the artificially triggered landslide. These fully automated sensors are more flexible than the conventional inclinometers by several orders of magnitude and therefore are able to detect fine movements (< 1 mm) of the soil mass reliably. Data from high-frequency measurements of the external bending work, indicating the transmitted energy from the surrounding soil to these sensors, pore water pressure at various depths, horizontal soil pressure and advanced surface monitoring techniques, contributed to an integrated analysis of the processes that led to triggering of the landslide. Precursors of movements were detected before the failure using the horizontal earth pressure measurements, as well as surface and subsurface movement records. The measurements showed accelerating increases of the horizontal earth pressure in the compression zone of the unstable area and external bending work applied to the slope deformation sensors. These data are compared to the pore water pressure and volumetric water content changes leading to failure.Geo-engineerin
Modelling of landslides in a scree slope induced by groundwater and rainfall
No full textPredicting the trigger of a slope failure of a steep Alpine scree slope in south-west Switzerland is challenging. The groundwater (GW) flow from snow-melting and rainfall infiltration during summer changes the susceptibility to surficial failure, which also depends on the slope angle, bedrock geometry, stratigraphy and the shear strength of the soil. Surficial failure mechanisms are investigated using prototype ground models that integrate input from field monitoring, geological observations and soil properties and account for relevant factors and constraints for physical and numerical modelling. Shallow scree deposits overlying various bedrock configurations (parallel to the slope, with and without a step) were tested under two hydrological regimes: GW flow, and GW combined with additional intense rainfall. Numerical modelling was used to study the parameter combinations that would lead to failure, and worst-case scenarios were defined in terms of the bedrock geometry and hydraulic perturbations. These results were verified using advanced physical modelling techniques in a geotechnical drum centrifuge. Physical modelling results indicated that, for a given GW condition, slope stability decreases (a) as the depth of the soil cover over the bedrock decreases and (b) the higher the bedrock step. Furthermore, a bedrock step impacts the volume and the location of the triggered failure. Rainfall exacerbates the situation.Geo-engineerin
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