連続設置される透過型砂防堰堤の確率的巨礫捕捉性能評価

摘要

砂防堰堤の目的は，上流ポケットに土砂を貯留することで下流域への土砂災害を軽減するものであり，このうち透過型砂防堰堤は土石流流体力が大きい土石流ピーク時の砂礫を効率的に捕捉できることから数多く建設されるようになってきだ）。この効率的土砂捕捉機能は，通常時には開口部から砂礫を下流に供給することで上流ポケットの土砂捕捉空間が確保され，土石流時には巨礫によって透過部を閉塞させることで不透過型堰堤と同様な土砂捕捉機能が発揮されることによる。%In planning for the arrangement of countermeasures in such a basin where has a large amount of sediment discharge, a series of grid check dam structures will be constructed. In this case, decision making of the space between steel pipes in consideration of change of characteristic of sediment rocks is substantial because characteristic of sediment rocks is used for design of grid check dam structures, and it change when it pass through the grid .This paper discusses an evaluation method of effect of grid shape on the probability of rocks capturing, and then an evaluation of effect of a series of grid check dam structures on the probability of rocks capturing. First, it is assumed that the capturing events are based on a probability process, I.e., a geometric distribution in a Bernoulli sequence. Second, the probability of what a rectangular space is stuffed by some rocks following log-normal distribution diameter is estimated using Monte-Carlo simulation. Third, in cases where same dam models were arranged at upstream and downstream, the number of rocks captured by the dam at downstream is less than 20% of number of rocks that pass through the dam at upstream. Fourth, in cases where the dam at downstream is designed to account for characteristic of rocks that pass through the dam at upstream, the number of rocks captured by the dam at downstream is about 50%.