| Popis: |
Stepped chutes are commonly used for overtopping protection for embankment dams. Aerated flow is commonly associated with stepped chutes if the chute has sufficient length. The aeration and turbulence of the flow can create a significant amount of splash over the training wall if not appropriately accounted for in the design of the structure. According to the United States Department of Agriculture (USDA)-Natural Resources Conservation Service (NRCS) Technical Release 60 Earth Dams and Reservoirs, a structural spillway should be designed to pass the freeboard hydrograph such that it does not cause serious damage to the embankment or the structure itself. For stepped spillways, researchers have suggested the training wall height equal a design factor, ranging from 1.4 to 1.5, multiplied by the bulked flow depth, y90. Yet, literature suggest that the design factor is a recommendation with little to no research provided to actually quantify what the design factor should be. Researchers at the USDA-Agricultural Research Service (ARS) Hydraulic Engineering Research Unit (HERU) in Stillwater, OK conducted a series of tests in a near prototype scale stepped chute facility to determine the design factor for training walls necessary to minimize the erosive splash that could result from the aerated flow. Tests were conducted in a stepped chute with a slope of 18.4 degree for a wide range of skimming flow conditions. Data indicates for a step height, h, to critical flow depth, dc, ratio of less than 0.4, the design factor for the training wall is 1.4, thus the training wall height is equal to 1.4y90. For h/dc ≥ 0.4, the design factor increases from 1.4 at h/dc = 0.4 up to 2.0 for h/dc = 1.0. These design factors are recommended for use on chute slopes ranging from 10 to 30 degrees. This research is intended to assist design engineers with appropriately designing stepped chute training walls to minimize the erosive splash that can occur as a result of aerated, turbulent flow. |
