| As one of the most effective measures of soil and water conservation, check dam was widely distributed in the Loess Plateau of China, which has a considerable influence on the local production and living. The drainage building of shaft type is one of the main discharge structure forms of check dam, during its actual operation, the occurrence of adverse flow pattern where free flow and full flow alternately appear and the negative pressure zone all bring great risks to the safety of buildings and dams. However, due to the particularity of its structure and operating conditions, it is not clear yet about the flow and pressure characteristics in the process of discharge. In this paper, the experimental study on the drainage structure of shaft type was carried out, and the reasons for the destruction of the discharge structure were explored from the angle of hydraulics. And by simulating the process of dam break through the model, the influence of dam break on the dynamic process of gully erosion were discussed. The results of the study would provide a scientific basis for the design of drainage structures of shaft type. The main conclusions were as follows:(1) Based on the physical model test and the numerical simulation method, this paper analyzed the hydraulic characteristics of the drainage structure of the shaft type under the conditions of clear water and sediment laden flow. The results showed that its discharge state were divided into three parts including influent from shaft wall, influent from annular weir and shaft wall and flow controlled by horizontal pipe. The calculation formula of the flow coefficient during the state of influent from shaft wall was improved with a better fitting degree.The discharge coefficient of sediment laden flow was slightly larger than that of clear water.(2) The influence of water head and sediment concentration on the pressure characteristics of the drainage structure of shaft type under two conditions were analyzed. The results showed that the pressure characteristics were closely related to the discharge state. When in the state of combined influent from annular weir and shaft wall, the pulsating intensity of the measuring point in the shaft under the condition of clear water was larger than that of sediment laden flow, while that of the measuring point near the inlet both showed an opposite trend under the state of combined influent from annular weir and shaft wall as well as flow controlled by horizontal pipe. The frequency domain analysis of the sediment laden flow showed that a higher sediment concentration was more prone to create a large vortex. If the sediment concentration was taken into consideration, cavitation may occur in the drainage structure of shaft type. The flow patterns in the shaft and horizontal tube were intuitively reflected by numerical simulation.(3) Wangmaogou watershed was selected to simulate the dam break inversion, by which the change process of water level in front of the dam, peak flow and erosion power in the main channel and the dam system unit were analyzed. The results showed that there were four dam units where dam break happened in the Wangmaogou watershed, among which the water level process of unit outlet in Sidizui, Kanghegou and Huangbaigou unit were influenced by the dam break and the check dam at the outlet of the watershed, which was Huangbaigou No.1, should be heightened to restrain the erosion energy in the basin. The runoff erosion energy along the channel under the condition of overtopping was less than that of non-dam condition. The dam land could cut down the peak effect to a certain extent,which had a positive effect on the safety of flood control... |
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