Study On The Mechanism Of Spur-Dike Water Damage Based On Fluid-solid Coupling

The spur dike is the most common hydraulic structure of channel regulation engineering in mountainous areas.The channel would be narrowed after the spur dike was built,and the horizontal channel would guide the flow and sand.Local circulation would be formed to wash and silt the channel so the riverbed morphology would be improved.The river bank and dykes would be protected to keep the water depth of the channel,so as to make the channel meet the requirements of navigation standards.However,as the spur dam is in a harsh environment,it would be influenced by complicated factors like the effects of water flow and the shape of the river bed.Therefore,there would be frequent spur water damage.In order to effectively prevent or reduce the occurrence of spur dikes damage,it is necessary to adopt new technical methods to continuously promote the design and construction of waterway regulation projects.Based on the fluid-solid coupling theory,adopting the finite element numerical simulation method,combined with the data of the "7.11 flood" flood damage survey data of the No.4 spur dam in the Jinxi reservoir area of the Jialing River in Sichuan Province in 2018,this paper researched the flow-structure and stability mechanism.And the preliminary results as follows:(1)Combining the data of 4 # spur dam and Jialing River "7.11 flood",adopting the channel regulation standards and other common methods,a series of calculation and analysis on spur dam scouring depth,block stable weight,anti-slide stability etc.have been analyzed according to different flow rates and different water depths.The result showed that excessive flow velocity,deep water depth,insufficient weight of the dam block,and easy erosion of the dam foundation were the main causes of water damage to the spur dam.Under normal circumstances,when the flow velocity reaches 3m/s and the water level is high(2m above the dam crest),the spur dam would suffer from the water damage.The higher the flow speeds,the greater the water depth,and the more serious the water damage would be.(2)Based on the CAE simulation platform Workbench of ANSYS,the coupling numerical model of water-spur dam is established.Through the numerical simulation results,the distribution structure of the flow structure at the head and body of the spur dike during the water damage is obtained.At the head of spur dike,due to the low velocity,the flow structure of the spur dike has a tendency of circumfluence,and the flow over the spur dike shows a slightly downward trend.Due to the water blocking effect of the spur dike at the dam body,an ascending current is formed on the Facing of the water slope,and the flow velocity at the top of the dam would increase.In addition,the water flow structure behind the dam presents obvious bottom flow and surface flow.With the increase of the underflow velocity,the velocity of surface flow decreased,so the flow would scour the riverbed at the foot of back water slope.With the increase of velocity and the water level,the flow trend around the dam head would be getting weak.After crossing the dam,the velocity of dam crest and subduction is increasing,so the scour effect on the slope foot and the top of the slope would be increased.After the dam structure was destroyed,the water flow structure returned to relatively stable at its original position.However,there is still similar flow structure displayed at the place where the displaced stones are.And the flow structure remains relatively stable when it is far from the dam.(3)Through the numerical simulation and comparison calculation of the water damage of the spur dam at the flow rates of 2m/s and 4m/s,it shows the water damage failure of the spur dam is plastic damage.When the flow speed is of 2m/s,the dam body basically remains stable.When the velocity of 4m/s,part of the dam body of the dam head was completely damaged.And most of the filling stones would be taken away by the flood,then the dam body would be completely damaged with a small part of the dam body stones remained.The block stones at the root of the dam also shifted under the action of water flow,and the original shape of the dam was partially destroyed.The simulation results are basically consistent with the on-site investigation.(4)The research results of this paper provides reference for the design and construction of spur dikes for waterway regulation in mountainous areas.