| In recent years,because of the decrease of water and sand entering into the lower reaches of the Yellow River,there is a series of new problems appeared,such as the existing projects cannot effectively control the river regime and serious beach erosion,etc.Taking a section of the lower reaches of the Yellow River as an engineering background,an assembled concrete permeable pile dam was designed.Furthermore,a two-dimensional hydrodynamic model of the reach is constructed by using MIKE21 FM.Finally,the differences between concrete permeable pile dam and traditional dam spur dikes were analyzed.The above research can provide some reference for river regulation in the lower reaches of the Yellow River.The main conclusions of this paper are as follows:(1)Through the study of key parameters of pile dam design,it is known that pile diameter,space,angle of incidence and number of rows have certain influence on the flow velocity of cross section behind the dam.The change of pile diameter will mainly change the length of dam axis,which will affect the guiding effect.The larger the pile diameter,the better the guiding effect,the lower the flow velocity behind the dam,the better the effect of slow flow and sediment deposition of pile dams.The change of spacing has no significant effect on pile dams.When the diameter of piles is 1.2 m,the critical space is 0.6m,the corresponding permeability is 33.3%.This situation is the critical point.When the space is more than 0.6m,the flow capacity behind the dam increases,and the area of the low velocity area behind the dam decreases.The change of incidence angle can significantly change the flow field around the pile dam,and with the increase of incidence angle,the guiding effect of the pile-dam system is continuously strengthened.The increase of the row number of pile-dam arrangement can significantly increase the area of the low velocity area behind the dam.The flow rate can be reduced by 40%maximally.(2)According to the results of parameter optimization,the main technical indexes of pile dam are analyzed and calculated,and the assembled concrete permeable pile dam in the lower reaches of the Yellow River is designed.The design discharges are 4000 m~3/s and 800 m~3/s respectively,and the design water level is corresponding to the flow level.The design scour depth is finally determined to be 15 meters by combining theory with practice,and the embedded depth is finally determined to be 10 meters by calculation;design pile diameter is1.2m,design pile net space is 0.6m,corresponding permeability is 33.3%.Based on the above parameters,a new type of concrete permeable pile dam is designed as an assembled structure.The pile dams are linearly arranged at equal distances.Shallow dams are set between the piles and dams to strengthen river regime control in non-flood season,and engineering bridges are set on the upper part to strengthen the stability of the pile-dam system.Bored pile sinking is selected for construction method.In addition,the bearing capacity of pile dam strengthened by prefabricating pile dam.(3)Taking a reach of the lower Yellow River as engineering background,a two-dimension hydrodynamic model of MIKE21 FM is established by using the measured topographic data and hydrological data in 2017,and the parameters are calibrated.Based on this model,the different effects on rivers caused by pile dams and spur dikes are studied.The results show that spur dikes and pile dams have some effects on the water level and velocity distribution of rivers,and the diversion effect of spur dikes is stronger than that of pile dams.This may be due to the fact that the boundary conditions are not taken into account in this paper,the difference between them is not significant.In addition,pile dams have a series of advantages that traditional spur dikes do not have,such as stable foundation,rapid construction,and relatively small ecological disturbance,which is conducive to the survival and reproduction of benthic organisms. |
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