Stability of A-Jack concrete block armors protecting the riverbeds

Abstract

Flip buckets are among one of the most common types of energy dissipaters, especially for dams. The scouring phenomenon occurs when falling jets hit the river bed, and A-Jack concrete block armors can be used as an effective way to control such a phenomenon. The main purpose of this study is to investigate the stability of sediment particles using A-Jack concrete block armors. In this regard, the general form of the incipient motion and incipient failure of A-Jack armor were extracted based on dimensional analysis and particle stability analysis. In these analyses, the dimensionless parameter of stability number denoted by SN is a function of other variables. The results of different physical models for different hydraulic conditions and sediment sizes are evaluated. Variability of SN related to each variable is considered, and linear and non-linear models for prediction of breakage conditions of the A-Jack block are derived. Using the experimental results, several empirical relations were developed to predict the incipient motion and incipient failure for different protection alternatives under different conditions of A-Jack block. By defining the bed scour as a criterion for the stability of A-Jack block, a design relation was also proposed to determine the required block size. Other topics investigated and discussed in this paper include effects of size and type of A-jacks as well as criteria for a gravel filter.