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1.
The impact force to a rigid obstruction from a granular mass sliding down a smooth incline provides insights into the solid-like and fluid-like behaviors of granular avalanches and useful information for risk assessment and engineering design against landslides. In this study, a series of 2-D flume tests were performed to systematically investigate the effects of inclination angle, sliding distance, and initial relative density on the flow front velocity and impact force on a rigid obstruction. The experimental results show that for inclination angles smaller than the critical state friction angle of sand, an increase in the sliding distance and/or initial relative density results in smaller impact forces; for higher inclination angles, the trend is reversed. Based on the experimental results, an analytical equation is proposed to estimate the flow front velocity and an empirical approach is presented to estimate the maximum impact force based on elastic solid and hydrodynamic methods. The proposed equations are found to provide more accurate predictions for the maximum impact force than similar equations in the literature. 相似文献
2.
A hypoplastic constitutive model for debris materials 总被引：1，自引：1，他引：0
Debris flow is a very common and destructive natural hazard in mountainous regions. Pore water pressure is the major triggering factor in the initiation of debris flow. Excessive pore water pressure is also observed during the runout and deposition of debris flow. Debris materials are normally treated as solid particle–viscous fluid mixture in the constitutive modeling. A suitable constitutive model which can capture the solid-like and fluid-like behavior of solid–fluid mixture should have the capability to describe the developing of pore water pressure (or effective stresses) in the initiation stage and determine the residual effective stresses exactly. In this paper, a constitutive model of debris materials is developed based on a framework where a static portion for the frictional behavior and a dynamic portion for the viscous behavior are combined. The frictional behavior is described by a hypoplastic model with critical state for granular materials. The model performance is demonstrated by simulating undrained simple shear tests of saturated sand, which are particularly relevant for the initiation of debris flows. The partial and full liquefaction of saturated granular material under undrained condition is reproduced by the hypoplastic model. The viscous behavior is described by the tensor form of a modified Bagnold’s theory for solid–fluid suspension, in which the drag force of the interstitial fluid and the particle collisions are considered. The complete model by combining the static and dynamic parts is used to simulate two annular shear tests. The predicted residual strength in the quasi-static stage combined with the stresses in the flowing stage agrees well with the experimental data. The non-quadratic dependence between the stresses and the shear rate in the slow shear stage for the relatively dense specimens is captured. 相似文献
3.
A paper recently published by Bartelt and Buser (hereafter identified as “the authors”) aims to clarify relationships between granular dilatancy and dispersive pressure and to question the effective stress principle and its application to shallow granular avalanches (Bartelt and Buser in Act Geotech 11:549–557, 2). The paper also criticizes our own recent work, which utilizes the concepts of evolving dilatancy and effective stress to model the initiation and dynamics of water-saturated landslides and debris flows. Here we first explain why we largely agree with the authors’ views of dilatancy and dispersive pressure as they apply to depth-integrated granular avalanche models, and why we disagree with their views of effective stress and pore-fluid pressure. We conclude by explaining why the authors’ characterization of our recently developed D-Claw model is inaccurate. 相似文献
4.
颗粒流是高速远程滑坡物质演化过程的一个重要阶段,也是从细观角度揭示其超常运动特性的重要手段.颗粒流所采用的主要研究方法以及取得的重要理论成果,可以为高速远程滑坡动力学机理的研究提供重要的技术手段和理论支持.本文聚焦颗粒流研究进展,从颗粒流基本概念、流态特征及流变本构模型、颗粒流粒径分选机制等方面进行了系统梳理;进而,从理论、实验及数值计算模型3个方面对高速远程滑坡研究中颗粒流理论及方法的应用进行了系统性述评;在此基础上,提出了从颗粒流角度研究高速远程滑坡动力学机理涉及的关键科学问题:高速远程滑坡高流动性的起源涉及哪些物理过程？如何量化和模拟其多分散性和破碎过程？如何量化描述颗粒尺寸分布的时空演变及其与流动的耦合？如何从其沉积特征中探究流动的传播机制？针对这些问题,从基于沉积学特征的颗粒流物理力学过程、考虑尺度效应的颗粒流动力学特性研究、基于颗粒流力学过程的滑坡运动机理及其本构模型、新技术新方法的应用4个方面提出下一步应重点开展的研究工作. 相似文献
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Here we investigate three long-standing principles of granular mechanics and avalanche science: dilatancy, effective stress and dispersive pressure. We first show how the three principles are mechanically interrelated: Shearing of a particle ensemble creates a mechanical energy flux associated with random particle movements (scattering). Because the particle scattering is inhibited at the basal boundary, there is a spontaneous rise in the center of mass of the particle ensemble (dilatancy). This rise is connected to a change in potential energy. When the center of mass rises, there is a corresponding reaction at the base of the flow that is coupled to the vertical acceleration of the ensemble. This inertial stress is the dispersive pressure. Dilatancy is therefore not well connected to effective-stress-type relations, rather the energy fluxes describing the configurational changes of the particle ensemble. The strict application of energy principles has far-reaching implications for the modeling of avalanches and debris flows and other dangerous geophysical hazards. 相似文献
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From the understanding of dynamics and processes of rapid granular flows and the granular-segregation mechanism in gravity-driven flow, we can clarify the particle-composition structure in the downstream areas of avalanches in geophysical contexts, such as landslides, rock falls, and snow-slab avalanches. Such dynamics also provide a basis for geophysical studies. This study experimentally investigates the dynamic behavior and segregation phenomena of a density-bidisperse, rapid, granular flow down a quasi-2D, rough, inclined rectangular chute. Particles with two density ratios are used to investigate the mechanism of density-induced segregation, and four chute-inclination angles are tested to examine the influence of driving forces. The dynamics of the mixture flow—which includes the flow-depth evolution, stream-wise and depth-wise velocity profiles, shear rate, and granular temperature in the upper high-shear band of the flow—are obtained from particle image velocimetry (PIV) measurements. The two-dimensional concentration distributions of the particles in the stream-wise direction are also obtained using 2D image processing to determine the segregation state. In the upstream region, the variation in the concentration of heavier particles is defined as the strength of the density-induced segregation state, Sd. Our results indicate that the mixture-flow parameter—particularly the shear rate and the granular temperature in the upper high-shear band—crucially influence the strength of particle segregation in granular avalanches. In the upstream region, a higher shear rate and a higher granular temperature in the upper high-velocity band result in a smaller drag force in the mixture flow, causing stronger density-induced particle segregation. These results well describe the entire processes of dense granular flows, from upstream initiation to the downstream steady state. Therefore, they reveal the structure of the mixed flow in the depth direction and are expected to explain various gravity-driven mixture granular flows.
相似文献7.
Modelling and numerical simulation of two-phase debris flows 总被引：1，自引：0，他引：1
Gravity-driven geophysical mass flows often consist of fluid–sediment mixtures. The contemporary presence of a fluid and a granular phase determines a complicated fluid-like and solid-like behaviour. The present paper adopts the mixture theory to incorporate the two phases and describe their respective movements. For the granular phase, a Mohr–Coulomb plasticity is employed to describe the relationship between normal and shear stresses, while for the fluid phase, the viscous Newtonian fluid is taken into account. At the basal topography, a Coulomb sliding condition for the solid phase and a Navier’s sliding condition for the fluid phase are satisfied, while the top free surface is traction-free for both the phases. For the interactive forces between the phases, the buoyancy force and viscous drag force are included. The established governing equations are expressed in a curvilinear coordinate system embedded in a curvilinear reference basal surface, above which an arbitrary shallow basal topography is permitted. Taking into account the typical length characteristics of such geophysical mass flows, the “thin-layer” approximation is assumed, so that a depth integration can be performed to simplify the governing equations. The resulting strongly nonlinear partial differential equations (PDEs) are first simplified and then analysed for a steady state in a travelling coordinate system. We find the current model can reproduce the characteristic shape of some flow fronts. Additionally, a stability analysis for steady uniform flows is performed to demonstrate the development of roll waves that means instabilities grow up and become clearly distinguishable waves. Furthermore, we numerically solve the resulting PDEs to investigate general unsteady flows down a curved surface by means of a high-resolution non-oscillatory central difference scheme with the total variation diminishing property. The dynamic behaviours of the granular and fluid phases, especially, the effects of the drag force and the fluid bed friction are discussed. These investigations can enhance the understanding of physics behind natural debris flows. 相似文献
8.
Soil–water interaction is a pivotal process in many underwater geohazards such as underwater landslides where soil sediments gradually evolve into turbidity currents after interactions with ambient water. Due to the large deformations, multiphase interactions and phase changes this involves, investigations from numerical modelling of the transition process have been limited so far. This study explores a simple numerical replication of such soil–water mixing with respect to changes in average strength using smoothed particle hydrodynamics (SPH). A uniform viscoplastic model is used for both the solid-like and fluid-like SPH particles. The proposed numerical solution scheme is verified by single-phase dam break tests and multiphase simple shear tests. SPH combinations of solid-like and fluid-like particles can replicate the clay–water mixture as long as the liquidity index of the solid-like particles is larger than unity. The proposed numerical scheme is shown to capture key features of an underwater landslide such as hydroplaning, water entrainment and wave generation and thus shows promise as a tool to simulate the whole process of subaquatic geohazards involving solid–fluid transition during mass transport. 相似文献
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流态化运动是高速远程滑坡的主要运动形式,是揭示高速远程滑坡运动机理的重要基础。基于粒子图像测速（PIV）分析方法,采用物理模型试验对不同粒径组成条件下的颗粒流内部的速度分布、剪切变形及流态特征进行了研究,并对高速远程滑坡流态化运动特征进行了讨论分析。结果表明:碎屑流流态化运动特征与颗粒粒径呈显著的相关性,随着粒径的减小或细颗粒含量的增加,颗粒流底部相对于边界的滑动速度以及整体的运动速度均呈逐渐减小的趋势,颗粒流内部剪切变形程度增加,颗粒的运动形式由“滑动”向“流动”转变;当颗粒粒径较小或细颗粒含量较高时,颗粒流内部剪切速率增大的趋势在颗粒流底部更加显著,反映了粒径减小有助于促进颗粒流内部剪切向底部的集中;在同一颗粒流的不同运动阶段及不同纵向深度,其流态特征具有显著差别,颗粒流前缘及尾部主要呈惯性态,颗粒间以碰撞作用为主,而主体部分则主要呈密集态,颗粒间以摩擦接触作用为主;在颗粒流表面及底部,颗粒间相互作用方式主要是碰撞作用,中间部分则以摩擦作用为主;对于不同粒径的颗粒流,随着粒径的增大或粗颗粒含量的增加,颗粒流内部颗粒的碰撞作用加强,颗粒流整体趋于向惯性态转变。 相似文献
11.
In this paper some observations and their analysis are presented dealing with the link between seismic signals and avalanche flow. The measurements during the passage of avalanches showed a specific spindle pattern which was quite different from the one of natural earthquakes. The general trend strongly depended on the topographic features of the avalanche path, and as a result we could estimate avalanche velocity. The running power spectrum showed a meaningful shift of the dominant peak from the front to the rear part of the flow. 相似文献
12.
D. M. McClung 《Natural Hazards》2014,72(2):1139-1158
Since human triggering is responsible for about 90 % of deaths from slab avalanches in Europe and North America, risk analysis is very important for skier triggering of avalanches. The depth to the weak layer and the slope angle are two key measureable quantities prior to dry slab avalanche release. Both are important in risk analysis. The probability of avalanche release dramatically increases as the slope angle increases above 25°. As the slab depth increases, the consequences increase rapidly if an avalanche releases. Simple risk analyses for skier triggering were done for both slope angle and slab depth. The slab depth analysis showed there is a range of about 0.6–1.0 m for which the risk of death is highest. For slope angles, the range with highest risk was shown to be 33°–45° within the known range (25°–55°) for skier-triggered avalanches. 相似文献
13.
Crushability is one of the important behaviors of granular materials particularly under high stress states, and affects both the deformability and strength of the materials that are in essence associated with state‐dependent dilatancy. In this presentation, first, a new critical state model is proposed to take into account the three different modes of compressive deformation of crushable granular materials, i.e. particle rearrangement, particle crushing and pseudo‐elastic deformation. Second, the governing equations for cavity expansion in crushable granulates are introduced, in which the state‐dependent dilatancy as well as the bounding surface plasticity model are used. Then, the procedure to obtain semi‐analytical solutions to cavity expansion in the material is described in detail, in which a commercial differential equation solver is employed. Finally, cavity expansion analyses are carried out on Toyoura sand, a well‐documented granular material, to demonstrate the effects of crushability and state‐dependent dilatancy. The study shows that particle crushing does occur at both high stress and critical states and affects the stress fields and the deformation behavior of the material surrounding the cavity in association with state‐dependent dilatancy. This leads to conclusion that particle crushing and state‐dependent dilatancy have to be taken into account when cavity expansion theory is used to interpret cone penetration tests and pressuremeter tests. Copyright © 2011 John Wiley & Sons, Ltd. 相似文献
14.
On the modeling of the state dependency of granular soils 总被引：3，自引：0，他引：3
Experimental studies have revealed that principal elements of the mechanical behavior of granular soils like the angles of internal peak friction and dilatancy are highly influenced by the combined effect of soil density and mean principal effective stress. In the literature, various empirical correlations between these elements and some parameters indicating soil state have been suggested. Herein, by using two well-known empirical expressions for state dependent peak friction and dilatancy angles, proper constitutive equations are derived and implemented in a stress ratio-based bounding surface plasticity framework. It is shown that the modified model is capable of simulating sand response in either loose or dense states using a unique set of parameters. 相似文献
15.
青藏高原东缘是全球重要的活动构造区,高原峡谷区斜坡陡峻,高位崩滑灾害多发。采用遥感解译、地面调查、钻孔勘探及测年分析等方法,研究了西藏洛隆察达沟和易贡扎木弄沟两处高位崩滑堆积体的多动力多期次演化特征。研究结果表明：(1)沿陡峻沟道发生的高位崩滑灾害多为复合成因,兼具内动力和外动力作用交替促发特征;(2)洛隆察达沟晚更新世以来的堆积物形成序列可分为4期,分别经历了以冰川作用为主的冰碛物堆积、古地震引发的高位崩滑-碎屑流堆积、气候变暖背景下的冰-岩崩滑堆积及近代重力崩滑堆积;(3)易贡扎木弄沟在过去5500年中,先后发生了8次以上较大规模崩滑堆积,测年结果显示了巨型崩滑事件存在百年数量级的复发周期,由于不同期次巨型崩滑体的成因不同,复发周期可能存在长、中、短的差异;(4)近年来受全球气候变化影响,冰-岩崩滑灾害频现,可能成为高原峡谷区高位远程地质灾害研究的焦点。本文关于高位崩滑灾害多期次演化过程的认识对于高原峡谷区重大地质灾害防灾减灾具有一定启示意义。 相似文献
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In this paper, we present a unified numerical framework for granular modelling. A constitutive model capable of describing both quasi-static and dynamic behaviours of granular material is developed. Two types of particle interactions controlling the mechanical responses, frictional contact and collision, are considered by a hypoplastic model and a Bagnold-type rheology relation, respectively. The model makes no use of concepts like yield stress or flow initiation criterion. A smooth transition between the solid-like and fluid-like behaviour is achieved. The Smoothed Particle Hydrodynamics method is employed as the unified numerical tool for both solid and fluid regimes. The numerical model is validated by simulating element tests under both quasi-static and flowing conditions. We further proceed to study three boundary value problems, i.e. collapse of a granular pile on a flat plane, and granular flows on an inclined plane and in a rotating drum. 相似文献
17.
冰-岩碎屑流是一种发育在高寒山区、含固态水的特殊碎屑流,具有超强的运动性。冰屑对提高冰-岩碎屑流运动性至关重要,但对其认识仍较为不足。通过对2000年易贡滑坡的灾史资料分析和野外调查,指出易贡滑坡启动时携带冰川冰体、运动时铲刮含冰碎屑物,而且具有规模大、冲出距离远的运动特性,是典型的冰-岩碎屑流。进而引入斜槽实验模拟岩土体上覆冰川冰体失稳下滑的过程,验证调查发现的堆积体前端坑洞群问题,探讨冰-岩碎屑材料冲出距离与含冰量、冰屑岩屑粒径比的关系。研究发现,冰屑可能包裹在碎屑流前端并全程参与碎屑流运动,在停积后由于融化而在堆积体上形成坑洞。被包裹的冰屑能够提高冰-岩碎屑材料的冲出距离,但含冰量较大时冰屑可能由于黏结成团、不易进入碎屑流内部而导致冲出距离变小。由此归结得到,冰屑提高碎屑流冲出距离的一个重要前提为冰屑进入碎屑流内部,当冰屑与岩屑的粒径比越小时冰屑越容易进入。这项研究工作为认识冰屑影响提供了坑洞调查法和斜槽实验法,研究成果有助于更为深入地认识冰-岩碎屑流运动特性的冰屑影响机理,为预防冰-岩碎屑流的远程致灾提供科学依据。 相似文献
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Snow avalanches are a significant hazard in mountainous environments around the world. This paper investigates the major February 1986 avalanche cycle that occurred in the western United States, and broadly analyzes the avalanche, snowpack, and weather conditions at twenty sites. These analyses suggest that the avalanche cycle resulted from the interaction of a relatively `normal' snowpack with an exceptional storm event, which was particularly noteworthy for the amount of precipitation it produced. Composited 500-hPa anomaly maps show the event resulted from an uncommonly persistent blocking pattern that resulted in a strong zonal flow and copious moisture being funneled over the western United States. Understanding severe and widespread avalanche cycles may improve our long-term forecasting of these events, and help mitigate theresulting avalanche activity. 相似文献
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