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Landslides - The frictional resistance of rock and debris is supposed to induce stress anisotropy in the unsteady, non-uniform flow of gravitational mass flows, including debris flows. Though... 相似文献
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The simulation of geophysical mass flows, including debris flows, rock and snow avalanches, has become an important tool in engineering hazard assessment. Especially the runout and deposition behaviour of observed and expected mass flows are of interest. When being confronted with the evaluation of model performance and sensitivity, there are no standard, objective approaches. In this contribution, we review methods that have been used in literature and outline a new approach to quantitatively compare 2D simulations of observed and simulated deposition pattern. Our proposed method is based on the comparison of normalized partial areas which can be plotted in a ternary diagram to visualize the degree of over- and under-estimation. Results can be summed up by a single metric between -1 (no fit) and 1 (perfect fit). This study shall help developers and end-users of simulation models to better understand model behaviour and provides a possibility for comparison of model results, independent of simulation platform and type of mass flow. 相似文献
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Christian Scheidl Michael Chiari Roland Kaitna Matthias Müllegger Alexander Krawtschuk Thomas Zimmermann Dirk Proske 《Surveys in Geophysics》2013,34(1):121-140
The objective of this study is to analyse adaptable debris-flow impact models, which are very important for mitigation measurements and buildings using their sphere of influence. For this reason, 16 debris-flow experiments, on a small-scale modelling approach, were performed. Impact forces were measured with a force plate panel, consisting of 24 aluminium devices, coaxially mounted with resistance strain gauges. Flow velocities, flow heights as well as horizontal impact forces were sampled with a frequency of 2.4 kHz. Sub datasets of sampled raw force data were defined by applying an average median filter, a low-pass filter routine. Further, estimated peak pressure values as well as empirical coefficients of hydraulic impact models were compared, and the influence of signal processing is discussed. 相似文献
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The internal deformation within debris flows holds essential information on dynamics and flow resistance of such mass-wasting processes. Systematic measurements of velocity profiles in real-scale debris flows are not yet available. Additionally, data on basal stresses of the solid and the fluid phase are rare. Here, we present and analyse measurements of vertical velocity profiles in two debris flows naturally occurring in the Gadria Creek, Italy. The method is based on cross-correlation of paired conductivity signals from an array of sensors installed on a fin-shaped wall located in the middle of the channel. Additionally, we measure normal stress and pore fluid pressure by two force plates with integrated pressure transducers. We find internal deformation throughout the flows. Only at the very front was some en-bloc movement observed. Velocity profiles varied from front to tail and between flows. For one debris flow, pore fluid pressure close to normal stress was measured, whereas the other flow was less liquefied. The median shear rates were mostly less than 5 s−1 and Savage numbers at the basal layer ranged from 0.01 to 1. Our results highlight the variable nature of debris flows and provide quantitative data on shear rate and basal stress distribution to help guide model development for hazard assessment and landscape evolution. © 2020 The Authors. Earth Surface Processes and Landforms published by John Wiley & Sons Ltd. 相似文献
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Large rock–ice avalanches have attracted attention from scientists for decades and some of these events have caused high numbers of fatalities. A relation between rock slope instabilities in cold high mountain areas and climate change is currently becoming more evident and questions about possible consequences and hazard scenarios in densely populated high mountain regions leading beyond historical precedence are rising. To improve hazard assessment of potential rock–ice avalanches, their mobility is a critical factor. This contribution is an attempt to unravel driving factors for the mobility of large rock–ice avalanches by synthesizing results from physical laboratory experiments and empirical data from 64 rock–ice avalanches with volumes >1x106 m3 from glacierized high mountain regions around the world. The influence of avalanche volume, water and ice content, low‐friction surfaces, and topography on the apparent coefficient of friction (as a measure of mobility) is assessed. In laboratory experiments granular ice in the moving mass was found to reduce bulk friction up to 20% while water led to a reduction around 50% for completely saturated material compared with dry flows. Evidence for the effects of water as a key driving factor to enhance mobility was also found in the empirical data, while the influence of the ice content could not be confirmed to be of much relevance in nature. Besides liquefaction, it was confirmed that mobility increases with volumes and that frictional surface characteristics such as flow paths over glaciers are also dominant variables determining mass movement mobility. Effects of the topography along the flow path as well as channeling are assumed to be other critical factors. The results provide an empirical basis to roughly account for different path and flow characteristics of large rock–ice avalanches and to find appropriate ranges for friction parameters for scenario modeling and hazard assessments. Copyright © 2011 John Wiley & Sons, Ltd. 相似文献
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In order to describe the flow behaviour of debris flows often rheologic models are used. This study introduces two novel facilities
to determine rheologic parameters of different models for debris flow material mixtures containing grain sizes larger than
to be measured in standard viscometers. The diameter of the vertically rotating flume (VRF) is 2.5 m, the rectangular cross
section has a width of 0.45 m, and the maximum rotational speed is around 30 revolutions per minute, corresponding to a mean
speed of the examined mixture of ∼4 m/s. From the measured flow parameters total boundary shear stress and corresponding shear
rate of the flowing mixture are derived. The ball measuring system (BMS) consists of a sphere that is dragged at specific
speeds across a sample of 0.5 l volume with the help of a small sphere holder. Accordingly torques due to drag exerted on
the sphere and its holder as well as corresponding speeds are measured and transformed into values of shear stress and shear
rate based on the method of Metzner and Otto. Material taken from fresh debris flow deposits in Eastern Switzerland have been
investigated with both facilities. We present results from experiments involving mixtures with different sediment concentrations
and with grain sizes up to 5 mm. Although estimated from completely different approaches the rheologic parameters of the independent
measurements are generally in reasonable agreement. 相似文献
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