Design and development of a riprap work having resistivity against overtopping flow on soil embankment.

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The purpose of the Research Project Is to investigate hydraulic and mechanical properties of rockfill and to propose a design procedure of riprap work that effectively resist against overtopping flow on soil embankment. Rock has been advantageously employed in hydraulic structures such as rockfill dams, flow-through embankments, rubble weirs and riprap works. To predict a flow transmissibility of the rockfill structure, an accurate evaluation of head loss property of flow through rockfill is required. In the Research Project, a head loss equation of flow through rockfill that is applicable to a wide range of rock particle size is proposed. A quadratic equation is selected to describe the head loss property of flow through rock fill. Two nonlinear coefficients included in the equation are effectively determined as a function of a hydraulic mean radius of rockfill voids based on laboratory tests using river gravel 5 to 75 mm in diameter. It is shown that the head loss equation of flow determined can be well applied to predict the flow transmissibility of rockfill structures without any consideration of scale effect of flow. A numerical experiment is conducted to estimate an amount of laminar flow composing the flow through rockfill. The laminar flow is found to be negligible even in the flow through a small size structure constructed using small rock particles. A parameter estimation procedure that employs a simple genetic algorithm combined with FEM calculation is also developed to determine the nonlinear coefficients in the head loss equation from a stage-discharge rate data observed in the laboratory or in the field/ Investigations of the mechanical property of rockfill as well as of soil erosion in an underlying foundation that have been left behind this two-year project will be tackled successively by the Head Investigator.