Morphology and Substrate Control on the Dynamics of Flowlike Landslides

A numerical model set up to simulate rapid flowlike landslide motion across three-dimensional terrain has been used to investigate the capability of various constitutive relationships to model the dynamics of complex events characterized by a changing type of substrate and morphology (e.g., glacier, bends). The numerical procedure is based on a continuum mechanics approach and on depth-averaged St. Venant equations for shallow flows. The developed RASH3D code includes the possibility of using several rheological laws, whose parameter values can vary along the runout path. Two rock avalanche cases, with some morphological peculiarities along the propagation path, have been numerically back-analyzed with both a frictional and a Voellmy rheology. Of the two considered rheologies, the Voellmy model produces the most consistent results in terms of runout area as well as velocity values. The main drawbacks of the frictional model are the tendency to predict excessive spreading of the mass and to overestimate the velocities. The results show that, when a complex problem of runout of rapid flowlike landslides has to be analyzed, it is necessary to have detailed knowledge of the geological and morphological features and to resort to increasingly complex rheologies.     

1D Modeling of Mud∕Debris Unsteady Flows

The National Weather Service 1D dynamic flood routing model FLDWAV is enhanced to include capability of modeling mud∕debris unsteady flows by including an additional friction slope term in the momentum equation of the Saint-Venant equations. Three techniques are incorporated into the model to determine the mud∕debris related friction slope term due to the internal viscous dissipation of non-Newtonian fluids and granular sliding friction of coarse-grained debris surges. These techniques are tested and some computational results are compared with observed field data and experimental data.     

1D Numerical Model of Muddy Subaqueous and Subaerial Debris Flows

A 1D numerical model of the downslope flow and deposition of muddy subaerial and subaqueous debris flows is presented. The model incorporates the Herschel-Bulkley and bilinear rheologies of viscoplastic fluid. The more familiar Bingham model is integrated into the Herschel-Bulkley rheological model. The conservation equations of mass and momentum of single-phase laminar debris flow are layer-integrated using the slender flow approximation. They are then expressed in a Lagrangian framework and solved numerically using an explicit finite difference scheme. Starting from a given initial shape, a debris flow is allowed to collapse and propagate over a specified topography. Comparison between the model predictions and laboratory experiments shows reasonable agreement. The model is used to study the effect of the ambient fluid density, initial shape of the failed mass, and rheological model on the simulated propagation of the front and runout characteristics of muddy debris flows. It is found that initial failure shape influences the front velocity but has little bearing on the final deposit shape. In the Bingham model, the excess of shear stress above the yield strength is proportional to the strain rate to the first power. This exponent is free to vary in the Herschel-Bulkley model. When it is set at a value lower than unity, the resulting final deposits are thicker and shorter than in the case of the Bingham rheology. The final deposit resulting from the bilinear model is longer and thinner than that from the Bingham model due to the fact that the debris flow is allowed to act as a Newtonian fluid at low shear rate in the bilinear model.     

Modeling Landslide Dambreak Flood Magnitudes: Case Study

Landslide dams typically comprise unconsolidated and poorly sorted material and are vulnerable to rapid failure and breaching, resulting in significant and sudden flood risk downstream. Hence they constitute a serious natural hazard, and rapid assessment of the likely peak flow rate is required to enable preparation of adequate mitigation strategies. To determine the relative utility and accuracy of dambreak flood forecasts, field estimates of peak outflow rates from the failure of the Poerua landslide dam in October 1999 were compared with estimates from physical laboratory modeling, empirical methods, and computer modeling. There was reasonable agreement among the field estimates, laboratory modeling, and computer modeling. Some empirical estimates were less reliable. Reasonably reliable estimates of peak outflow can be obtained from computer model routines sufficiently rapidly to be of use in an emergency management situation. The laboratory modeling demonstrated the effect of dam batter slopes and valley bed slope on peak outflow; this information could be used to refine empirical or numerical estimates of peak outflow.     

Experiments on Reworking by Successive Unconfined Subaqueous and Subaerial Muddy Debris Flows

Debris flows occur under water, e.g., in lakes and the ocean, as well as under air. These two types of debris flow have many similarities, but also differ in striking ways. The focus of the research reported here is on the ability of an unconfined debris flow to remobilize or rework an antecedent deposit over which it runs. Experiments were performed in a tank in order to quantify reworking. The debris slurry was premixed and consisted of a mixture of water, sand, and kaolinite clay. Three experiments were performed, each consisting of four individual runs. In each run the slurry was released impulsively from a head tank. The first run of each experiment formed a deposit over the initial inerodible bed. The second, third, and fourth runs progressed over and reworked to a greater or lesser extent the antecedent deposit(s). Two experiments of four runs each were performed in the subaqueous configuration, and one experiment of four runs was performed in the subaerial configuration. In the subaerial case, reworking was immediate and extensive. In the subaqueous case, reworking of the deposit of the first run by the second run was suppressed. Part of the reason for this appears to be hydroplaning of the head of the debris flow. As the deposit built up, however, considerable reworking was eventually observed in the subaqueous case as well.     

Large Deformation Finite-Element Analysis of Submarine Landslide Interaction with Embedded Pipelines

Submarine landslides represent one of the most significant geohazards on the continental slope in respect of the risk they pose to infrastructure such as deep water pipelines. A numerical approach, based on the finite-element method but using remeshing, was established in this paper to simulate large flow deformation of debris from a landslide and to quantify the loads and displacements imposed on pipelines embedded in the seabed. A simple two-dimensional elastic perfectly plastic soil model with plane strain conditions was employed in this analysis. The pipeline was restrained by a set of springs so that the load on the pipeline built up to a stable value, representing the limiting load at which the debris flowed over the pipeline. A parametric study was undertaken by varying the pipeline embedment and the relative strengths of the debris and seabed. The analysis results show that the various combinations of soil strength and embedment depth lead to different debris-pipeline movement patterns and consequently lead to rather different magnitudes of the loads imposed on pipelines. The pipeline is subjected to the largest load (an equivalent pressure of 11.5 times debris strength) from the landslide when it rests on the weakest seabed. The pressure is proportional to the debris material strength but varies inversely with the seabed strength for partially embedded pipelines. For all strength combinations, there is a critical embedment depth beyond which the force on the pipeline reduces to a very small magnitude.     

Analysis of Debris Wave Development with One-Dimensional Shallow-Water Equations

The objective of this contribution is to analyze the formation of debris waves in natural channels. Numerical simulations are carried out with a 1D code, based on shallow-water equations and on the weighted averaged flux method. The numerical code represents the incised channel geometry with a power-law relation between local width and flow depth and accounts for all source terms in the momentum equation. The debris mixture is treated as a homogeneous fluid over a fixed bottom, whose rheological behavior alternatively follows Herschel-Bulkley, Bingham, or generalized viscoplastic models. The code is first validated by applying it to dam-break tests on mudflows down a laboratory chute and verifying its efficiency in the simulation of rapid transients. Then, following the analytical method developed by Trowbridge, the stability of a uniform flow for a generalized viscoplastic fluid is examined, showing that debris flows become unstable for Froude numbers well below 1. Applications of the code to real debris flow events in the Cortina d’Ampezzo area (Dolomites) are presented and compared with available measured hydrographs. A statistical analysis of debris waves shows that a good representation of wave statistics can be obtained with a proper calibration of rheological parameters. Finally, it is shown that a minimum duration of debris event and channel length are required for waves showing up, and an explanation, confirmed both by field data and numerical simulations, is provided.     

Landslide Hazard Evaluation: The Landslide Hazard Curves

This paper presents an innovative, practical methodology to establish priorities for slope monitoring and the planning of stabilization works in large hilly areas. The study is based on the analysis of geological and geomorphological maps, identification of catchment areas, and the division of catchment areas into primary (with main stream) and secondary (without main stream) sub-basins. Attention was focused on secondary sub-basins and their characteristics: lithology; an ad hoc parameter q (related to the average rainfall, the size of the basin, and the width of the toe section), and the average slope inclination i. The technique presented enables the “landslide hazard curve,” unique for a given formation in homogenous areas with similar rainfall conditions and seismicity, to be drawn in a chart which features q and i. All the ascertained and assumed unstable areas represented in the chart are located above the landslide hazard curve.?The study was carried out scientifically by taking into account engineering aspects (geological, geomorphological, hydrological, and geotechnical), which influence slope stability. Groundwater levels, important in mapping out landslide prone areas, were considered in the study by means of the parameter q.     

基于信息量模型与ArcGIS的龙南县足洞地区滑坡危险性评价

针对龙南县足洞地区滑坡地质灾害,对研究区进行野外详细地质调查,分析工程地质岩组、坡度、边坡高程、地质构造及人类活动等对滑坡的影响,结合斜坡稳定性影响因素选定滑坡危险性评价因子,采用层次分析法计算加权信息量模型并利用ArcGIS软件对研究区进行滑坡危险性评价分区,得到研究区滑坡灾害危险区划分图及相关统计信息,结果表明:区内稀土矿山的池浸、堆浸及原地浸矿等人工活动对滑坡灾害影响最大,高程及坡度其次,坡向影响最小,稀土矿山采场应作为研究区重点滑坡防治及监测区域,评价结果与研究区实际情况一致性较好.      

Cellular-Automata Model for Dense-Snow Avalanches

This paper introduces a three-dimensional model for simulating dense-snow avalanches, based on the numerical method of cellular automata. This method allows one to study the complex behavior of the avalanche by dividing it into small elements, whose interaction is described by simple laws, obtaining a reduction of the computational power needed to perform a three-dimensional simulation. Similar models by several authors have been used to model rock avalanches, mud and lava flows, and debris avalanches. A peculiar aspect of avalanche dynamics, i.e., the mechanisms of erosion of the snowpack and deposition of material from the avalanche is taken into account in the model. The capability of the proposed approach has been illustrated by modeling three documented avalanches that occurred in Susa Valley (Western Italian Alps). Despite the qualitative observations used for calibration, the proposed method is able to reproduce the correct three-dimensional avalanche path, using a digital terrain model, and the order of magnitude of the avalanche deposit volume.     

基于模糊频率比与熵指数的滑坡易发性评价——以崇义县为例

为进一步优化基于频率比模型的滑坡易发性评价,构建了一种基于模糊频率比-熵指数的滑坡易发性评价模型。该模型将模糊信息分配的基本原理及方法引入频率比的计算中,优化了基于滑坡易发性影响因子分级的滑坡信息量统计,提出了模糊频率比的计算方法。在此基础上,建立了模糊频率比与熵指数相结合的滑坡易发性评价模型。以崇义县为例,基于对地质环境和滑坡空间分布特征的系统分析,提取了11个滑坡评价影响因子,构建了滑坡易发性评价指标体系。应用结果表明,与单一的频率比、频率比-熵指数两种模型相比,预测精度可分别提高7.5%和3.6%,高和极高易发区的滑坡频率占比达85.98%,预测成功率曲线的AUC值达0.863 7,均优于未进行频率比模糊优化的评价模型,表明该模型是一种有效且可靠的滑坡易发性评价模型。      

Generic Process Mapping and Simulation Methodology for Integrating Site Layout and Operations Planning in Construction

The present research is intended to address dynamic construction-process simulation methods, with a focus on how to effectively model resource transit among various activity locations in the site system. Following a review of basic simulation paradigms and recent research developments, we propose a new process mapping and simulation methodology for modeling construction operations. The simulation algorithm is presented and the process mapping procedure is illustrated step by step using an earth-moving example featuring technology and resource constraints. It is straightforward to convert the resultant process mapping model describing workflows and resource flows over site locations into a simulation model. A STROBOSCOPE model is formed for the same problem definition to contrast and cross-validate our methodology with the established activity cycle diagram-based modeling approach. One additional case of modeling the concreting site operations by the hoist and barrow method is also given to demonstrate the application of the proposed methodology in practical settings.     

Dynamic Model for Subcritical Combining Flows in Channel Junctions

A one-dimensional theoretical model for subcritical flows in combining open channel junctions is developed. Typical examples of these junctions are encountered in urban water treatment plants, irrigation and drainage canals, and natural river systems. The model is based on applying the momentum principle in the streamwise direction to two control volumes in the junction together with overall mass conservation. Given the inflow discharges and the downstream depth, the proposed model solves for each of the upstream depths. The interfacial shear force between the two control volumes, the boundary friction force, and the separation zone shear force downstream of the lateral channel entrance are included. Predictions based on the proposed approach are shown to compare favorably with existing experimental data, previous theories, and conventional junction modeling approaches. The main advantages of the proposed model are that the proposed model does not assume equal upstream depths and that the dynamic treatment of the junction flow is consistent with that of the channel reaches in a network model.     

地质灾害治理工程勘查设计和施工中的难点分析

由于人们对自然环境的破环以及自然周期性运动的引发,形成了泥石流、地震、暴雨、山体滑坡等地质灾害,而且不断呈现出上升趋势。其治理因地形地貌、岩体结构、水文地质、气候环境不同,大大增加了治理难度。如何降低和预防各种地质灾害成为亟待解决的难题。     

A mathematical model of the heat and fluid flows in direct-chill casting of aluminum sheet ingots and billets

A finite-element method model for the time-dependent heat and fluid flows that develop during direct-chill (DC) semicontinuous casting of aluminium ingots is presented. Thermal convection and turbulence are included in the model formulation and, in the mushy zone, the momentum equations are modified with a Darcy-type source term dependent on the liquid fraction. The boundary conditions involve calculations of the air gap along the mold wall as well as the heat transfer to the falling water film with forced convection, nucleate boiling, and film boiling. The mold wall and the starting block are included in the computational domain. In the start-up period of the casting, the ingot domain expands over the starting-block level. The numerical method applies a fractional-step method for the dynamic Navier-Stokes equations and the “streamline upwind Petrov-Galerkin” (SUPG) method for mixed diffusion and convection in the momentum and energy equations. The modeling of the start-up period of the casting is demonstrated and compared to temperature measurements in an AA1050 200×600 mm sheet ingot.     

基于虚拟材料复模量非均匀分布的螺栓连接薄板结构半解析建模

基于非均匀分布的虚拟材料模拟螺栓连接薄板搭接部分的力学特性,其中虚拟材料的材料参数用复模量表示,可直接生成复刚度矩阵以表示搭接部分的刚度及阻尼特性,省却了常规建模中生成结合部阻尼矩阵的步骤,在保证模型精确性的基础上简化了建模流程,以此建立了螺栓连接薄板结构的半解析模型并对其进行了动力学分析。首先描述了建模理念,将虚拟材料分别假定了三种复模量非均匀分布形式模拟螺栓搭接部分的力学特性,提出用反推辨识技术确定虚拟材料储能模量与耗能模量的方法。接着,基于能量法并用正交多项式假定模态,推导了螺栓连接薄板的半解析分析模型,并创新性地给出了求解半解析模型任意锤击点与拾振点处频响函数的公式。最后,以一个具体的螺栓连接薄板结构为对象进行了实例研究,结果表明:用所创建的半解析模型计算出的各阶仿真固有频率与实验测得的各阶固有频率的误差均在5%以内,计算得到的各阶仿真模态振型以及频响函数曲线与实测值均较为接近,从而证明了利用复模量非均匀分布的虚拟材料模拟螺栓搭接部分可有效简化螺栓结合部建模,亦可达到较高的仿真计算精度。      

Finite-Element Analysis and Vibration Testing of a Two-Span Masonry Arch Bridge

This paper presents the analytical modeling, modal testing, and finite-element model updating for a two-span masonry arch bridge. An Ottoman masonry arch bridge built in the 19th century and located at Camlihemsin, Rize, Turkey is selected as an example. Analytical modal analysis is performed on the developed 3D finite-element model of the bridge to obtain dynamic characteristics. The ambient vibration tests are conducted under natural excitation such as human walking. The operational modal analysis is carried out using peak picking method in the frequency domain and stochastic subspace identification method in the time domain, and dynamic characteristics (natural frequencies, mode shapes, and damping ratios) are determined experimentally. Finite-element model of the bridge is updated to minimize the differences between analytically and experimentally estimated dynamic characteristics by changing boundary conditions. At the end of the study, maximum differences in the natural frequencies are reduced on average from 18 to 7% and a good agreement is found between analytical and experimental dynamic characteristics after finite-element model updating.     

Geographic Information Systems-Based Three-Dimensional Critical Slope Stability Analysis and Landslide Hazard Assessment

In this paper, by combining the geographic information systems (GIS) spatial analysis function and a hydrologic analysis and modeling tool with a column-based three-dimensional (3D) slope stability analysis model, a new GIS grid-based 3D deterministic model has been developed for slope stability analysis. Assuming the initial slip as the lower half of an ellipsoid, the identification of the 3D critical slip surface in the 3D slope stability analysis is performed by means of a minimization of the 3D safety factor using Monte Carlo random simulation. By using this hydrologic analysis and modeling tool, dividing the whole study area into slope units, and taking each slope unit as a study object, the minimum 3D safety factor for each slope unit can be obtained, and the landslide hazard can then be mapped for the whole study area.