Research on Bifurcation Property of Dike Rockfill of River Closure by End Dumping

College of Conservancy and Hydropower Engineering, Wuhan University, Wuhan 430072, China

Funding project：髙校博士学科点专项科研基金项目资助（98049303） Received: 2000-10-30 Revised: 2000-12-18 Available online: 2001-06-20

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Abstract

The dike slope slumping with high frequency and on large scale is a new and important problem in river closure by end dumping with deep water and low velocity. According to the characteristics of two kinds of slump phenomena, this article firstly analyzes and summarizes quantitatively the factors that influence the slump, which include the erosion resistance of the placed material, the erosion resistance of dike foundation, the water depth of the closure mouth, the mechanical property of dumping material and the absorbed water moisture of material. In addition, it indicates that the last three factors mainly determine whether the slump occurs and on what scale the slump occurs in the water closure with deep water and low velocity. Secondly, a micro model which describes the structure of the rockfill is adopted, and the research on the bifurcation property of the static balance equation, the type of its universal unfolding and its transition set is made by application of static bifurcation and singularity theory in nonlinear systems in the following two circumstances： 1) the stress in rockfill (σ1) is regarded as a parameter while the elastic coefficient (K) of the springs that simulate the friction relation among the particles is considered a constant; 2) the coefficient K is regarded as a parameter and the stress σ1 is a constant. The study result shows that different bifurcation phenomena of the static balance equation will happen when the stress increases or the K decreases to some extent. Therefore, the change of stress in rockfill and the water-immersed materials have theoretically proved to be the fundamental cause of the slump with high frequency and on large scale. Thirdly, the engineering measures to handle it are put forward which include：1) the processing scheme and dumping strength should be arranged correctly according to the water depth of each part of the closure mouth; 2) apart from the structural need of the cofferdam, those dumping materials, which particle diameter of which is homogeneous and shape is near to global, should not be used as far as possible; 3) the mud content of the mixed riprap used widely should be reduced so as to lower the extent of water influence; 4) truck should not be driven to the end of the dike and not be unloaded to water directly so as to reduce the impact against the slope and the turbulence to the stress of the rockfill. Finally, the reason why slumping possibility and range are greater in model experiment than in the prototype is demonstrated.

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References

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