This paper presents a way to apply discontinuous deformation analysis (DDA) technique to rock fall simulations. In order to make the method meet the practical requirements, the original DDA has been improved in the following aspects: 1). reducing error from large rigid body rotation; 2). considering damping effect due to resistance in the air and drag force from plants on the surface; 3). considering energy loss from collision. It has been shown that the improved DDA is very efficient in rock fall analysis. The velocity and jump height of each falling stone can be easily estimated in detail for the whole falling path by DDA simulation. They are very helpful in the design of protective structures. A practical rock fall analysis has been made. The results are quite good in agreement with the experiment made on the same slope, and they were used to design new concrete walls to stop possible rock fall blocks coming into the adjacent road and railway.
In the mountainous country like Japan, rock fall is a very serious problem for maintaining roads, buildings and houses. Rock sheds, retaining walls and prevention nets and fences are usually used to mitigate the hazards. It is obvious that the knowledge about the motion behavior of falling stones, such as the falling paths, velocities and jump heights, is necessary for the design of these structures. Many experiments of falling stones on real slopes have been made in Japan. Some good experiences and empirical formulas have been obtained, even the Manual of the Countermeasure against Rock Falls (in Japanese) was drawn up by Japan Road Association in 1983. However, since the motion behavior of falling stones is closely related to the detail shape of a slope, it has been found that the manual is helpless for some slopes. According to this formula, one can find that it is almost impossible to make a prevention structure to stop a falling stone of 60tƒ from a height over 40m because of too large energy from the estimated velocity of 27m/sec. Therefore, the knowledge about the distribution of velocities and jump heights in the whole falling path is necessary for the analysis of rock fall. For this reason, we present a way to simulate the rock fall by use of the discontinuous deformation analysis (DDA) technique (Shi, 1989). In order to make the method meet the practical requirements from rock fall simulations, we, at first, make some improvements on the original DDA. This includes reduction of the error due to large rigid body rotation, consideration of motion damping effect due to resistance in the air and drag force from plants on the surface, and consideration of energy loss due to collision. It has been shown that the improved DDA is very efficient in rock fall simulations. The velocity and jump height of each falling stone can be easily estimated in detail for the whole falling path. They, obviously, are very useful in the design of protective structures.
