2017年7月九州北部豪雨における須川第一砂防堰堤の袖部を破壊させた原因の一考察

抄録

A part of the wing on the left bank of the Sugawa Daiichi sabo dam was destructed by woody debris or sediment discharge due to heavy rainfall in the northern part of Kyushu Island, July 2017. A large amount of woody debris was captured on the upstream of Sugawa Daiichi sabo dam, and the influence of woody debris has been considered to be one of the cause of the destruction. However, the load acting on the wing has not been analyzed and the causes of the destruction has not been clarified yet. In this report, each load (hydrostatic pressure, impact force of stone, impact force of woody debris, etc.) was estimated from data acquired during the field survey, several concrete cores were sampled from the sabo dam, and executing concrete strength tests. Structural calculation and stability calculation were carried out based on the estimation and concrete strength tests, and the cause of destruction was analyzed. Analysis result of the structural calculation shows that destruction did not occur only due to hydrostatic pressure and it was assumed that one of the reasons for destruction was that there was a construction joint with low strength. From the stability calculation it was confirmed that a part of the wing could fall due to the collision of multiple woody debris. The destruction of the wing was estimated to be caused by multiple woody debris colliding or multiple woody debris collided and fell after lower woody debris load acted.