Abstract

The authors analyze rock-fall problems of in-situ slope models at a road and dam site by using two and three dimensional discontinuous deformation analysis (2D and 3D-DDA). The objectives of the study are to clarify the dispersions of the rock-fall trajectories in the horizontal direction and the velocity changes in different rock shapes with vegetation on the slope using 3D-DDA. Four falling rock shapes, cubic, the twelve sided polygonal, the twenty sided polygonal and the eighty sided polygonal (ball) were introduced into the 3D-DDA models. It was found in this study the dispersions in the horizontal direction of the slope is larger for the cubic shape than the ball shapes. The falling velocities of rocks is larger for the ball shapes than the cubic shapes.

The influence of the vegetation, such as trees on the slopes, caused large direction changes and slowed down the velocities of the falling rocks. Therefore, the most important parameter for rock fall simulations in three dimensional analysis is the effect of rock shapes on velocities and trajectories. The advance over previous studies is the finding that the 3D-DDA analyses is useful for estimating the velocities of falling rocks in actual rock fall problems and subsequently to determine the design of the protective walls?? with trees as vegetation. On the other hand, conventional two dimensional analysis (2D-DDA) has been used for design of the protective walls against rock fall. Since, the above results from three dimensions could be introduced in the conventional two dimensional analysis, it will be possible to save on the total cost of design and construction work of rock fall countermeasures.

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