This paper proposes a simulation method on trap performance on the steel check dam subjected to woody debris flow by using 3 dimension distinct element method. The proposed method uses cylindrical elements for woody debris, and sphere elements for rock debris, respectively. Trap performance experiments are carried out by using water way and modeled structures, in advance. Segregation mechanism between woody debris and gravels, or large gravels and small gravels were observed. And trap performance of steel check dams, which have an intervals of pipe members, are checked with respect to contain ratio of woody debris, different ratio of gravel size and structural members interval. The proposed method shows reliable simulation of segregation mechanism and, trap mechanism of the structures as well as trap ratio of the debris.

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 This paper reports the results of a series of numerical experiments concerning the fundamental performance in solving three-dimensional (3D) seepage problems of finite elements using the Raviart-Thomas mixed interpolation method (RT), which is capable of independent interpolation of hydraulic head and velocity. In the conventional finite element method that uses only hydraulic head as an unknown variable, velocity is independently calculated for each element. There are cases, therefore, where a continuous velocity field cannot be determined with high accuracy. In the RT method, flux can be made continuous along common boundaries of adjacent elements because a velocity shape function is constructed by using the set of flux defined at the element faces as a degree of freedom. Furthermore, by means of formulation based on a hybrid variational principle, final variables can be reduced to the Lagrange multiplier. Although almost all of the previous studies have shown validity in solving two-dimensional problems, this study identifies the fundamental performance, including drawbacks, of 3D elements used in the RT method in solving seepage problems.

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 This paper presents segregation phenomena of spherical grains observed in a rolling cylinder and its analysis by using the DEM. The rolling cylinder experimental device in which grains flow down relatively along the rolling bottom plane and grains stay constantly in a position of rolling cylinder is proposed. Therefore grains movement in those groups can be observed. In experiment 3 size glass beads, one size nylon bead, and 3size harden coal ash beads are used, and two of them are combined as a sample. Segregation occurrence combination is categorized. Moving characteristics of large size grain and small size grain is discussed by analysis results of DEM as well as experimental observations.

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 A heavy rain fall hit Shobara city, Hiroshima on 16th July 2010. A large amount of woody debris caused a flooding disaster by damming up a bridge and spreading out to rice field and so on. This paper presents an inquiry on the shape properties of the woody debris left on the rice field. And simulations of the damming up process of woody debris occurred on the real bridge by using 3 dimensional Distinct Element Method based on assembled cylinder elements. The simulation points out the twisting mechanism of woody debris occurred at the space between slab of the bridge and the flood surface in damming up process. Validity of the simulation at real site is discussed.

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