Research On Spur Dike's Technical Status Evaluation Method In The Middle And Lower Reachers Of The Yangtze River

In the regulation engineering,the spur dike is one of the commonest regulating structures.The success of groyne works depends on remaining in a normal working condition.Hence,it has a profound significance to study how to evaluate the spur dike's technical status in an comprehensive,objective and scientific way.The main contents and results of this paper are as follows:(1)According to investigate the spur dikes' damage situation,the evaluation indexes are preliminarily selected,which are based on the investigation method,experts' investigation and scouring mechanism.The complex correlation coefficient of each index is calculated by the method of great uncorrelation and the relative indexes are eliminated.Finally,the evaluation indexes are confirmed and are listed as follow:(1)dam root: axial damaged length,transverse damaged length,notch height;(2)dam head: collapse length;(3)slope surface: damaged area,slope ratio;(4)dam surface: dam height,collapse depth,collapse length;(5)scour: depth,the distance between the deepest point and the axis of the dam,the slope of the scour.The collection of various indicators are also proposed.(2)Basing on investigating and analyzing the damage of spur dikes in the middle and lower reaches of the Yangtze Riverm,an evaluation index system for spur dike technical conditions was established.The evaluation index system of spur dike technical status is built.The rule layer is listed as follow: spur dike's structural attribution and changes in the scour.The index layer indicators are dam surface,slope surface,dam head,dam root,existing scour hole,and scouring trend.In addition,basing on analytic hierarchy process,each evaluation index's weight value is calculate.(3)In order to achieve quantitative evaluation,this paper proposes an evaluation method for spur dike technical conditions---the DER method and four levels of evaluation standards have been established.At the same time,in order to evaluate the technical status of a single index and the whole spur dike,a single technical condition index evaluation formula and an overall technical condition evaluation formula are proposed.(4)Different methods are used to determine the criterion of each evaluation index in this paper.For the dam head's index,it's considered that the channel's velocity influences the spur dike's technical status.Calculating the changes of velocity with different collapse length,the criteria of dam head is determined,with flow chart method.The other structural attribution indexes' criteria are confirmed through the existing specifications.For the scours' index,the criterion is decided by judging the relation between the scours' slope and the sediment's rest angle.For the technical index of scours' forecast,the coming flow and the sediment,the properties of the spur dike and the river bed's boundary conditions are analyzed to determine the input factors.Based on BP articical neural work,the model is built and the scours' changes are forecasted under the condition of large water and less sand.(5)With the evaluation model,four spur dikes on Zhangnan waterway in 2016 are evaluated.The scores are 98.3,96.6,98.9,98.9,respectively.The technical status is rated as the first class and is good.The evaluation process is quite simple and the evaluation model is reasonable.It is of high reliability and can be used as a reference for the channel maintenance department.