Recently, intensive rainfalls have been becoming heavier than past, and, therefore, landslide disasters have been often occurring in many area, and damage of various facilities and lives have been large. The slope failure disasters occurred by the heavy rainfall that typhoon 9 caused at western and northern area in Hyogo prefecture in 2009. Spatial and temporal prediction of landslides is important to diminish the damage by such landslides, and it is necessary to gather the information of dangerous situation for the evacuation of the habitants. The real-time type hazard system has been constructing at Rokko mountain area in Hyogo prefecture from 2007, and it have been operating from April 2010. In this system, the prediction method of probability of failure occurring, using digital elevation model that Okimura and Ichikawa suggest, is installed, and the data of topography, geotechnical information, rainfall are used to calculate the safety factors of each cell that change real-timely at heavy rainfall. As the predicted results have been evaluated by the actual data of landslides caused by the heavy rainfall in 1967 July, the validity of this model has been showed enough. In this paper, the function and performance of this system are showed.
This paper proposes an application of the distinct element method on damming up performance of drift wood capturing structures subjected to woody debris. In order to simulate the behavior of drift woods, a column shape element model is developed. In advance to analysis works, the debris flow experiments, with various combinations of the length of drift woods and the intervals of vertical columns of the structure, were carried out. Those results are utilized as a simulation object of the proposed method and a flow velocity modeling in this study. The flow velocity model used herein considered a turbulence of water flow occurred in the experiment. The turbulence model consists of combination of 3 kinds of turbulence effects, i.e., turbulence of water height by damming up, flow to avoid columns, and turbulence in the water. This paper pointed out that the simulation results by using the flow velocity model without the turbulence effect is not able to express the experimental results adequately. However, the simulation results by using the flow velocity model with the turbulence models show good agreement from the view point of debris capturing mechanism and debris flow capturing probability. Because the turbulences make the posture of the drift wood sway around the structures, which shorten the projection length to the column interval, tear down the temporary linked structure of the drift wood captured by columns, and/or flow to avoid the column.
A modified particle method for simulating highly concentrated granular flows is proposed based on a constitutive equation considering inter-particle stress. The particle method we use is based on the Moving Particle Semi-implicit (MPS) method, which has been originally proposed for calculation of incompressible viscous fluid flows with free surfaces. The MPS method is capable of simulating a wide variety of hydraulic problems such as solid-liquid two-phase flows, the blocking of a bridge by driftwood, and river embankment erosion. In spite of being a flexible tool for numerically simulating intense behavior of water and other types of fluids, original MPS is applicable only to Newtonian fluid flows. Some modifications are necessary in order to calculate highly concentrated granular flows with dilatant properties. First, the inter-particle stress term is introduced to the momentum equations by taking the divergence of inter-particle stress tensor derived by Tsubaki et al. (1982). The equations are further modified by adding a bed friction corrective term to take into account the effects of bed roughness and energy dissipation on the movable bed of debris flow. The proposed method is then applied to the simulation of debris flow experiments. A quantitative comparison is made between the velocity distributions predicted in the present method and the experimental and theoretical results for granular flow with a movable bed. Velocity profiles of modified MPS with an inflexion point are similar in shape to those measured and calculated by Tsubaki et al., while standard MPS encounters limitations in attaining appropriate profile curves.
This paper presents a numerical simulation of debris flow model by using modified Moving Particle Semi-implicit (MPS) method with solid and liquid particles. The modified MPS method is the Lagrangian model of solid-liquid flow phase and is proposed by combining the MPS method which was proposed by Koshizuka to simulate fluid dynamics with the Distinct Element Method (DEM). Herein, the contact between solid particles and the friction between solid particles and floor are taken into account. First, outline of the modified MPS method is described. Then, flow water simulation is compared with test result by using the original MPS method. After that, the effects of parameters in the modified MPS method are examined by comparing with the MPS method. Finally, the modified MPS method is applied to simulate the test result of debris flow model with pumice stone. The proposed method could reproduce the surge formation of debris flow model and load time history.
In 2004, Mizuyama proposed the shutter sabo dam, which is a sabo dam with a shutter that can be opened under control. Such a dam has the advantages of both closed and open sabo dams. Recently, shutter sabo dams have been constructed on some rivers. In this study, we simulated a shutter sabo dam in the Ashiarai-dani basin using the KANAKO simulator equipped with a graphical user interface. We compared the effectiveness of the shutter sabo dam according to differences in when the shutter was closed. We also compared situations with and without a movable riverbed. Comparing the sediment discharge downstream from the sabo dam and the riverbed deformation upstream from the sabo dam, earlier closing of the shutter was more effective at sediment control. However, when there is a movable riverbed, earlier closing causes more riverbed degradation downstream from the sabo dam. Therefore, to operate shutter sabo dams properly, it is necessary to obtain detailed information on the water-discharge rates, water levels, sediment-transport rates, and riverbed material.
Outburst flood of landslide dams induces catastrophic disasters. It's necessary to investigate into process of overtopping erosion and sediment transport to estimate at downstream disasters by overtopping erosion of landslide dam. The numerical simulation model concerning the overtopping erosion of a landslide dam has been proposed so far by Satofuka et al. and the applicability has been shown about the hydrograph and the peak discharge rate. However, the side bank erosion rate was given experienced constant, and there was a problem that the way to give the constant was difficult. The erosion of the bed progresses by overtopping and the phenomenon of the side bank collapses along with it is confirmed by the hydraulic model experiment. On the other hands, it has been proposed two-layer flow model applied to the two-dimensional numerical simulation by Takahama et al. So in this study, we applied slope collapse model proposed by Sekine to the model. As a result, The process which the erosion of the bed by overtopping, and the phenomenon of the side bank collapses along with it was able to be reproduced by considering the slope collapse of the side bank in the numerical simulation.