Trapping analysis of steel open�]type Sabo dam against debris flow by DEM representing protrusions of rock

Toshiyuki HORIGUCHI, Joji SHIMA, Tomoo MATSUBARA, Hiroshi TATEZAWA, Satoshi KATSUKI, Nobutaka ISHIKAWA and Takahisa MIZUYAMA

Recently many steel open�]type Sabo dams (hereafter, steel open dams) have been constructed in Japan. These structures consist of steel pipes, and they are designed to allow most soil and small gravel to pass downstream through the gaps. However, if the debris flow has occurred, the steel open dam can capture large rocks. This paper presents experimental and computational approaches to examine the trapping mechanism whereby rocks in a debris flow are captured by a steel open dam. First, a model test was performed by using a flume to examine the mechanism whereby rocks (gravels) in a debris flow are trapped by a steel open dam. Second, a new three�]dimensional distinct element method (3�]D DEM) was developed in which the rocks were modeled as assembled elements representing natural, irregularly shaped rocks. The assembled elements are consisted of six equally size spherical elements symmetrically arranged in the shape of a regular octahedron. The ratio of protrusions to the diameter of the spherical elements was termed the protruding coefficient β, which was determined by performing the angle of repose test at the site. Third, the proposed3�]D DEM was applied to simulate the trap performance of the model test. Finally, the projected trap performance and shape of sediment by the proposed DEM were compared with the model test result and the DEM using a single spherical element.