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一种流动性滑坡涌浪动力学模型
Abstract
Landslide-induced surge is a kind of secondary disasters triggered by waterside landslides. Generally, the endangering range in a landslide-induced surge far exceeds the motion area of the landslide, and accurately predicting spatial evolution of landslide-induced surge is of significant importance for disaster prevention. However, the existing models usually simplify landslides as rigid bodies, which is obviously against the fact that many landslides propagate in a flow-like way. Therefore, a numerical model was put forward in this paper to provide more reliable prediction results for landslide-induced surges. By treating slip masses as flow-like materials, the governing equations of landslide-water coupling motion were derived. Next, the governing equations were solved by the finite difference method, and the dynamic model that can simulate the evolutionary process of flow-like landslide-induced surge was established. Finally, the evolutionary
process of Gongjiafang landslide located at the Three Gorges of the Yangtze River was simulated by the model and the simulated maximum wave heights in the longitudinal section (i.e., the flow direction) of the river were compared with the measured data. Results show that the maximum wave height in this section appears in the main sliding direction of the landslide, and the maximum wave heights on both two sides decrease quickly. The simulated results agree well with the measured values. The established model can provide more adequate prediction of the influence range of landslide-induced surge.
The valley disaster chain has recently attracted the attention of academics, which is also a huge challenge in the construction and operation of the Sichuan-Tibet railway transportation corridor. This research gives the definition and components of the valley disaster chains. By review valley disaster chain events that have occurred, the characteristics of the valley disaster chain were summarized, and their evolution models were summarized. The key factors that affecting the valley disaster chain were also discussed. Then, the risk assessment system, prevention, and control countermeasures of the valley disaster chain were proposed. The conclusions were obtained as follows: 1) The valley disaster chain is composed of potential disasters, primary disasters, secondary disasters (or series), and disaster-bearing bodies. Their typical characteristics were summarized as time continuity, spatial continuity, causality, and chain evolution. Based on the primary disasters, the valley disaster chain can be divided into 3 categories and 11 sub-categories, including the landslide disaster chains, the debris flow disaster chains, and the glacial lake disaster chains, which can be formed by a combination of three key processes (collapse/landslide-clastic flow/debris flow, landslide/debris flow blocking the river, and dammed/glacial lake outburst). 2) The formation of the valley disaster chain includes two modes. One is that the physical and mechanical properties of the primary disaster mass changed during movement to form secondary disasters, the other is that the primary disaster body changes the boundary of the secondary disaster body that induces secondary disasters. 3) The risk assessment of the valley disaster chain should pay attention to both the initiation mechanism of the primary disaster and the chain generation mechanism of the secondary disasters. It is suggested to strengthen the identification accuracy of the source of the potential disaster, develop the scientific understanding of the disaster transformation process, and quantify the disaster transformation mechanisms and critical conditions, establish a numerical simulation and evaluation method for the valley disaster chain, and carry out the evolution process and risk assessment of the valley disaster chain under future scenarios; 4) The prevention and control of the valley disaster chain is still in its infancy and should be improved based on the scientific understanding of the disaster chain. A comprehensive system for early identification, monitoring and early warning, simulation evaluation, emergency response, engineering governance, emergency avoidance, and risk management of the valley disaster chain is needed in the future.
A gigantic rapid landslide claiming over 1,000 fatalities was triggered by rainfalls and a small nearby earthquake in the
Leyte Island, Philippines in 2006. The disaster presented the necessity of a new modeling technology for disaster risk preparedness
which simulates initiation and motion. This paper presents a new computer simulation integrating the initiation process triggered
by rainfalls and/or earthquakes and the development process to a rapid motion due to strength reduction and the entrainment
of deposits in the runout path. This simulation model LS-RAPID was developed from the geotechnical model for the motion of landslides (Sassa 1988) and its improved simulation model (Sassa et al. 2004b) and new knowledge obtained from a new dynamic loading ring shear apparatus (Sassa et al. 2004a). The examination of performance of each process in a simple imaginary slope addressed that the simulation model well simulated
the process of progressive failure, and development to a rapid landslide. The initiation process was compared to conventional
limit equilibrium stability analyses by changing pore pressure ratio. The simulation model started to move in a smaller pore
pressure ratio than the limit equilibrium stability analyses because of progressive failure. However, when a larger shear
deformation is set as the threshold for the start of strength reduction, the onset of landslide motion by the simulation agrees
with the cases where the factor of safety estimated by the limit equilibrium stability analyses equals to a unity. The field
investigation and the undrained dynamic loading ring shear tests on the 2006 Leyte landslide suggested that this landslide
was triggered by the combined effect of pore water pressure due to rains and a very small earthquake. The application of this
simulation model could well reproduce the initiation and the rapid long runout motion of the Leyte landslide.
KeywordsLeyte landslides-Computer simulation-Rapid landslides-Ring shear test
In this paper, a modified finite difference model is proposed to simulate the propagation of flowslides. Modifications of the new model are conducted by calculating the lateral pressure coefficient k in the sliding mass and the entrainment and centrifugal effect during the transport process. The strength parameters are modified based on the size of the entrainment to consider the change in the landslide strength due to material mixing. Two dam break problems are simulated to test the accuracy and stability of the numerical scheme, and the results show good agreement with the analytical solutions and the measured data. Then, the model is used to analyze a typical flowslide: the Dagou landslide in Gansu Province, China. The model can accurately predict the details of the motion of the landslide, especially behaviors such as turning along the meandering gully and thrusting on the gully slopes due to centrifugal force.
Based on the finite-volume method and a structured mesh system, a numerical model for simulating landslide-generated waves is developed. The governing equations are the two-dimensional nonlinear shallow water (NLSW) equations with the consideration of a dynamic seabed. The central upwind scheme is used to compute the numerical interface flux. The second-order MUSCL method for variables reconstruction, local bed modification and implicit treatment to bottom friction are used to ensure the properties of well-balanced, conservative and non-negative water depth, as well as the ability to deal with the moving shoreline. The second-order Runge-Kutta method with Strong Stability Preserving (SSP) is adopted to perform the time marching. A series of benchmark cases are simulated and the numerical results are compared with the analytical solution, experimental data and numerical results from other models. It is found the present model can simulate the generation, propagation and runup of the landslide-generated waves for the considered cases with reasonable accuracy. © 2017, Editorial Board of Advances in Water Science. All right reserved.
Landslides sliding into shallow water often block watercourses, and in addition landslide-induced impulse waves may result in risks to the safety of the reservoir or waterways over a wide area. Such impulse waves differ from those from landslides into deep water which slide underwater completely. This study conducted twenty-five groups of orthogonal experiments of landslide-induced impulse waves in shallow water where the Froude numbers ranged between 0.6 and 2.0. Based on the experimental results, dimensionless functions of the parameters such as amplitude, wavelength and jet-flow height of the initial landslide-induced waves in shallow water were derived. The predictions from these formulae are very close to those obtained from the experiments. Further, a source model of landslide-induced waves in shallow water was built based on formulae derived from the experiments, and wave propagation and run-up were calculated with the Boussinesq-type equations model. The newly built model of landslide-induced waves in shallow water was used to calculate and analyze two representative examples from landslides in the Three Gorges in China, namely the Qianjiangping landslide-induced impulse wave event and the Xintan landslide-induced impulse wave event. Comparison of the calculations with data from multiple sources indicated that our model for landslide-induced waves in shallow water had high accuracy. Our model for landslide-induced waves in shallow water may help in the predictive analysis of impulse waves and mitigation works for this type of event in reservoirs worldwide.
In this experimental study, granular material is released down slope to investigate landslide-generated waves. Starting with a known volume and initial position of the landslide source, detailed data are obtained on the velocity and thickness of the granular flow, the shape and location of the submarine landslide deposit, the amplitude and shape of the near-field wave, the far-field wave evolution, and the wave runup elevation on a smooth impermeable slope. The experiments are performed on a 6.7 m long 30° slope on which gravity accelerates the landslides into a 2.1 m wide and 33.0 m long wave flume that terminates with a 27° runup ramp. For a fixed landslide volume of 0.34 m³, tests are conducted in a range of still water depths from 0.05 to 0.50 m. Observations from high-speed cameras and measurements from wave probes indicate that the granular landslide moves as a long and thin train of material, and that only a portion of the landslide (termed the "effective mass") is engaged in activating the leading wave. The wave behavior is highly dependent on the water depth relative to the size of the landslide. In deeper water, the near-field wave behaves as a stable solitary-like wave, while in shallower water, the wave behaves as a breaking dissipative bore. Overall, the physical model observations are in good agreement with the results of existing empirical equations when the effective mass is used to predict the maximum near-field wave amplitude, the far-field amplitude, and the runup of tsunamis generated by granular landslides.
By combining landslide dynamics research and tsunami research, we present an integrated series of numerical models quantitatively simulating the complete evolution of a landslide-induced tsunami. The integrated model simulating the landslide initiation and motion uses measured landslide dynamic parameters from a high-stress undrained dynamic-loading ring shear apparatus. It provides the numerical data of a landslide mass entering and moving under water to the tsunami simulation model as the trigger of tsunami. The series of landslide and tsunami simulation models were applied to the 1792 Unzen-Mayuyama megaslide and the ensuing tsunami disaster, which is the largest landslide disaster, the largest volcanic disaster, and the largest landslide-induced tsunami disaster to have occurred in Japan. Both the 1792 megaslide and the tsunami portions of the disaster are well documented, making this an excellent test of the reliability and precision of the new simulation model. The simulated tsunami heights at the coasts well match the historical tsunami heights recorded by “Tsunami-Dome-Ishi” (a stone showing the tsunami reaching point) and memorial stone pillars.
A review is conducted of advances and developing trends over recent years in numerical methods for simulation of landslides and surges in four stages, including slope instability, slope sliding, surge generation, and propagation, in reservoir districts. The achievements in numerical methods for simulation of slope sliding and surge generation are summarized. It is pointed out that landslides and surges should be considered an integrated continuous process from the slope instability to surge propagation stages, and, based on current research of each stage, the relevant research methods of solid and fluid mechanics should be combined in future research, so as to construct numerical models for the entire simulation process of landslides and surges in reservoir districts. © 2016, Editorial Board of Advances in Science and Technology of Water Resources, Hohai University. All right reserved.
Large-scale landslide dams can induce significant hazards to human lives by blocking the river flows and causing inundation upstream. They may trigger severe outburst flooding that may devastate downstream areas once failed. Thus, the advancement in understanding the formation of landslide dams is highly necessary. This paper presents 3D numerical investigations of the formation of landslide dams in open fluid channels via the discrete element method (DEM) coupled with computational fluid dynamics (CFD). By employing this model, the influence of flow velocity on granular depositional morphology has been clarified. As the grains settle downwards in the fluid channel, positive excess water pressures are generated at the bottom region, reducing the total forces acting on the granular mass. In the meantime, the particle sedimentations into the fluid channel with high impacting velocities can generate fluid streams to flow backwards and forwards. The coupled hydraulic effects of excess water pressure and fluid flow would entrain the solid grains to move long distances along the channel. For simulations using different flow velocities, the larger the flow velocity is, the further distance the grains can be transported to. In this process, the solid grains move as a series of surges, with decreasing deposit lengths for the successive surges. The granular flux into the fluid channel has very little influence on the depositional pattern of particles, while it affects the particle–fluid interactions significantly. The results obtained from the DEM-CFD coupled simulations can reasonably explain the mechanisms of granular transportation and deposition in the formation of landslide dams in narrow rivers.
For slope failures on reservoir, we can't only see the damage from their deformation and failure, but also think about the disaster from the tsunami caused by them. This paper attempts to obtain the law about spread and attenuation of the reservoir tsunami caused by slope failure. It uses the software of FAST (Fast Assessing System for Tsunami) and GEO-WAVE to numerically simulate such tsunami. It selects the slope #4 at Gongjiafang on the Three Gorges reservoir as the actual case. The simulation area is about 23 km long and 10.4 km wide and the reservoir water levers are 175 m, 156 m and 145 m respectively. Figures about the tsunami are gained with the numerical simulation. The pictures of wave probes are charted with calculation and analysis of data processing module. Comparative analyses of simulation results under the three water levers are given. As water lever decreases, the largest wave height and the largest climbing height have an increasing tendency, but the time of wave damaging the passage gets shorter. The largest wave height has a distribution rule that the shape in middle of river is concave and the shapes on both sides of river are protuberant. The rapid attenuation area of impulse wave distributes in the region at a distance of 1 km from the source point. The higher is the wave height of source point, the more is the drop height of impulse wave in unit length. Because the waves can be superposed near bank, it is suggested that boats must speed through along the middle of the reservoir river immediately when they are near the slope #4.
Landslide-related impulse waves are catastrophic but accidental, so limited data on field measurements are available; scaled physical experiment is therefore a functional method to simulate and analyze this phenomenon. A large-scale physical Froude-similar model to produce impulse waves was constructed based on the Chinese Gongjiafang landslide, which occurred on the main stream of Three Gorges after the impounding in the reservoir in China. With a scale of 1:200, the model had the dimensions of 24, 8, and 1.3 m. Four water levels, 145, 156, 172.8, and 175 m, were modeled for the experiments, and marble coarse sands were used to imitate the actual cataclastic rock mass. Wave height gauges, high-speed cameras, and run-up measuring instruments were used to monitor wave fluctuations in the model. Among the experiments, the ones modeled using a water level of 172.8 m best confirmed the actual conditions in the Gongjiafang landslide, representing a good validation of the experiments. This study obtained, for the first time, specific data on the reproduced impulse waves’ convergence and superposition during propagation, and of the energy change between impulse waves and reflected waves. The test data describe a rapid decaying and gradual decaying rule for the wave heights and run-ups. The Froude-similar experiments presented in this article help us to understand the whole procedure of impulsive wave generated by cataclastic rock mass failure, and the results acquired contribute to studies of impulse waves caused by similar bank destabilizations worldwide.
[1] Subaerial landslide-tsunamis and impulse waves are caused by mass movements impacting into a water body, and the hazards they pose have to be reliably assessed. Empirical equations developed with physical Froude model studies can be an efficient method for such predictions. The present study improves this methodology and addresses two significant shortcomings in detail for the first time: these are the effect of three commonly ignored block model parameters and whether the slide is represented by a rigid block or a deformable granular material. A total of 144 block slide tests were conducted in a wave flume under systematic variation of three important block model parameters, the slide Froude number, the relative slide thickness, and the relative slide mass. Empirical equations for the maximum wave amplitude, height, and period as well as their evolution with propagation distance are derived. For most wave parameters, remarkably small data scatter is achieved. The combined influence of the three block model parameters affects the wave amplitude and wave height by up to a factor of two. The newly derived equations for block slides are then related to published equations for granular slides. This comparison reveals that block slides do not necessarily generate larger waves than granular slides, as often argued in the technical literature. In fact, it is shown that they may also generate significant smaller waves. The new findings can readily be integrated in existing hazard assessment methodologies, and they explain a large part of the discrepancy between previously published data.
Landslides can result in rocks and soil falling into reservoir at high velocity, thereby triggering large surface waves, which may threaten navigation vessels, dam stability, and lives and properties along the shore. This paper presents the results of an experimental study into surges caused by landslides entering reservoirs. First, eight factors — water depth, sliding impact velocity, slide volume, slide width, slide thickness, the mass of the slide blocks, sliding slope, and drop height of the mass center — were chosen as key parameters. Then, these were combined into four dimensionless factors: Froude number for sliding velocity, landslide scale, slide thickness and slide impact angle (radian measure). In addition, based on data from 145 model tests, empirical equations for prediction of the first and second impulsive wave heights were developed through nondimensional multiple linear regression analysis. These equations were applied to landslides triggered by the Wenchuan Earthquake along the shore of Zipingpu Reservoir. The calculated results were found to be in good agreement with field surveys and with calculations by other formulas; the proposed formula is believed preferable in that it incorporates dimension parameters and slope of the sliding surface.
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