| Spur dike is the most commonly used to regulate structure to improve navigation conditions of rivers in mountainous areas.It can restrain water and attack sand and increase navigation depth of ships.In the channel of mountainous rivers,the structure of spur dikes mostly adopts riprap structure with certain water permeability,but due to its water-resisting effect,especially the diversion of the head of the dike to upstream incoming water will change the flow structure and cause the riverbed to be washed out,thus causing the situation of spur dikes being destroyed by water.However,previous research measures on scouring of spur dikes are mostly focused on impervious spur dikes,so it is necessary to study the impact of water permeability characteristics of spur dikes on scouring of dike head area.In this thesis,physical generalization model test and theoretical analysis are used to study the scouring effect of upstream water on riverbed in dike head area by controlling different flow classes,void sizes,void ratios and void locations.The variation laws of depth,volume and width,length and maximum silting height of scouring pit behind permeable groin dike are mainly studied.At the same time,the scouring prevention measures for permeable spur dikes were put forward in combination with the existing scouring prevention measures for spur dikes.The main conclusions are as follows:(1)Scouring pit behind dike develops rapidly at the initial stage.Under different flow conditions,the larger the flow,the deeper the scouring pit behind dike and the larger the volume of scouring pit.The influence of void size and void ratio on scour pit behind the dike is relatively small.Under the same flow rate,the larger the void size,the shallower the depth of scour pit behind the dike and the smaller the volume of scour pit.The smaller the void ratio,the greater the depth and volume of scouring pit behind the dike,but smaller than that of solid spur dikes under the same flow rate.(2)Flow has a significant influence on Silting behind the dike.With the increase of flow,the width,length and maximum height of silting behind the dike increase to some extent.At the same flow rate,the larger the void size and void ratio,the smaller the width and length of transverse and longitudinal silting behind the dike,and the higher the maximum height of silting behind the dike.(3)With the same flow rate,void size and void ratio,the closer the void position of the permeable spur dike is to the dike head,the smaller the scouring pit depth and volume behind the dike,the smaller the width and length of transverse and longitudinal silting and the higher the maximum silting height.(4)Combining with the scouring prevention measures of spur dikes in the past,it is proposed to increase the void size and void ratio(the maximum void size in this thesis is D=32mm and the maximum void ratio is P=22.5%).At the same time,the dike is protected by pre-fabricated concrete or wire cage loaded with rubble to increase the self-weight of the dike body and by placing load-twisting accropode,etc.,and monitoring is strengthened during routine patrols,and maintenance is carried out according to the characteristics of water damage sites.Starting from the aspects of reducing scour behind dike and increasing stability of dike body,the stability of spur dike is enhanced.In conclusion,by changing the size,void ratio and position of the voids of the permeable groin,the riverbed scouring caused by the influence of the dike head can be reduced.The research results are of certain engineering significance for the study of anti-scouring measures of the permeable groin. |
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