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Taiwan have high and precipitous landform with plentiful rainfall, a high speed flow stream easily to cause a riverbed scrub and destroy structures, so to dredge stream become the most important work of preparedness against natural disaster. Stone sill is the most common protection river bed scouring structures on the transverse direction of rivers, due to some principles of easy to get material and tally with ecological landscape, material naturalized and the economically construction, only the analysis theory of stone sill entirety permutation in stability still need to be developed. In this study, we use the DDA (Discontinuous Deformation Analysis) method to build an analysis model, so that can understand the different permutation style of stone sill to the influenced of riverbeds’ stability. First, this study will review the solid-bed hydraulic engineering analysis and alignment model of abroad and internal wild stream, to be a mold of selection the stone size, permutation pattern, and as the main simulation object of the usually stream, to consider for two riverbed’s width of 6m and 10m, Use the three permutation methods: 8 word-type array, parabolic and uniform arrangement, even particle permutation in different rise-span ratio (1 / 3, 1 / 4, 1 / 6, 1 / 8) permutations and combinations, application DDA to find out the most suitable permutation under a different flow speed mode. The analysis result of this study showed differences in the proportion of rise-span ratio can significantly influence the stability, of the mode in every permutation shows the average displacement of 1/8 rise-span ratio will increase 390% ~ 726% than the 1/3 rise-span ratio. And in the different three permutation models, the 8 word-type array can sustain higher flow speed attack than other two models.
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