Author(s): Jau-Yau Lu; Jian-Hao Hong; Shu-Chun Ho

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Abstract: Grade-control structures can be used to stabilize the streambed and to protect the pier foundation against scour. However, considerable scour may occur downstream of the grade-control structures, which is so-called edge failure. The scour process downstream of the grade-control structures is an important issue of value to engineering practice. The main objective of this paper is to predict the geometrical parameters of the scour hole downstream of a low-head stepped grade-control structure. Experiments were carried out for two different flume slopes. The sediments used in the experiments were uniform sand and uniform gravel. Moreover, two ramp slopes of the grade-control structures were tested. The predicted maximum equilibrium scour depths and lengths of the scour holes agree well with the experimental data. Also, the computed temporal variations of the scour depth correspond closely with the measured data. In addition, an innovative device in the form of tetrahedron frame is placed downstream of the grade-control structure to test its effectiveness as an edge failure countermeasure. Although the device has previously been used to protect the river banks, it has not been tested as a sill-scour countermeasure. The results show that the average reduction of scour depth by placing tetrahedron frames downstream of the grade-control structure was about 83%.

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Year: 2009