Keywords: three-dimensional distinct element method, cylindrical element, anti drift wood structures, wood debris, drift wood, trap performance.

Recently many check dam structures have been constructed in the mountainous areas and play an important role as countermeasures to debris flow disasters in Japan. There are various shapes of check dams from the view point of the requirement performance. The open type of check dam is expected to be permeable for fine gravel and sand in the usual situation but to halt the huge rocks in debris flow. After stuffing, it works like a close type check dam which interrupts disastrous rock, gravel and soil in the debris flow. The permeability requirement comes from an environmental issue, i.e. the shortage of sand supply in the downstream area, environmental damage of plants, or fish mode of life and so on [1].

It is difficult to succeed in the contradictory demands by setting a proper interval for the structural elements [2]. Especially in the case that the debris flow contains woody debris, this setting policy does not work well based on real disaster observations. However, there is not much research work on the performance of an open check dam subjected to woody debris flow.

In order to ignore a complicated prediction for the performance of the check dam subjected the mixed debris of rocks and wood, a specific check dam, called anti-drift wood check dam in this study, has been constructed in these days. The drift wood check dam screens the drift woods at an upstream area. However, the performance of the anti-drift wood check dam has not been studied sufficiently.

This paper proposes an application of the three-dimensional distinct element method [3] for damming up performance of the anti-drift wood check dam subjected to a debris flow containing drift woods. In order to simulate the wood drift performance in the debris flow, the cylindrical element, i.e., its contact judgment and handling process and so on, is proposed. The scaled debris flow experiments associated with several wood debris containment ratios are carried out in advance.

The capturing process and drift wood performance obtained by simulation are in good agreement with the experimental one, which is a collision between drift woods and anti-drift woods structure, rotation, trapping and accumulation. The simulation results show good performance from the view point of the drift wood capturing mechanism and the capturing probability in terms of the ratio of the interval of structure to the wood length.

1

The Japanese Ministry of Land, Infrastructure, Transport and Tourism, "Technical Criteria for River Works: Practical Guide for Planning", Sankaido, 2005.

2

National Institute for Land and Infrastructure Management, Ministry of Land, Infrastructure and Transport, "Manual of Technical Standard for designing Sabo facilities against debris flow and driftwood", Technical Note of National Institute for Land and Infrastructure Management, No. 365, 2007.

3

P.A. Cundall, "A computer model for simulating progressive large scale movement in blocky rock system", Proc. Symp. ISRM, Nancy, France, 2, 129-136, 1971.

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