Slump Mechanism And Stability Of Deep-water Closure Dyke And Its Engineering Application

Difficulty of river closure used to be measured by velocity of flow, water drop and the like. Later, some experts and scholars concerned tried to perform study on comprehensive index to measure difficulty of river closure,, and advanced concepts of maximum flow energy in closure gap or maximum flow energy per unit width in closure gap and the relating formula was derived, which has been used to up now due to lack of examples of large-scale closure works, especially deep-water closure works, to verify it. Knowledge of closure difficulty has not been broken through until appearance of special example of deep-water closure of the main channel for the Three Gorges Project. What are characteristics of deep-water closure works? What are key difficulties in deep-water closure? How to establish theoretical model and find out resolution? What are the engineering measures and countermeasures to overcome the above difficulties? All those above-mentiond problems demand prompt solution in this field.Characteristics of deep-water: dumped stone materials are unable to roll down to the slope foot because of high dike and long slope; new stable slope can form only through repeatedly collapse; dike caving leads to unsteady of the dike nose.In order to attain hydraulic parameters in closure gap and so that present the needed condition for mathematical model solution of dyke nose slump, a mathematical model of current in river channel is established and its solution and engineering computation example are given. In establishing current mathematical model near the closure gap, two-dimensional model is usually adopted. Finite volume method is adopted in this paper thanks to its simplicity, flexibility, conservation type discrete pattern and non-necessity of linearization. For turbulent viscosity coefficient, zero equation model is adopted in this paper.Basic equations for two-dimensional mathematical model are consisted of continuous equation, momentum conservation equations in direction X (with the stream) and direction Y (against the stream) and corresponding closed turbulent flow equation.In finding out solution of the general microdifferential equation, finite volumemethod is used to discrete and establish a two-dimensional mathematical model of turbulence. Later, Simpler method is used to doing programming and calculation. Closure works of the main channel for the Three Gorges Project is selected as example for engineering computation. The given computation conditions consist of calculation scope and topography data, situation in stages of closure dike advancement, closure gap location and current condition. Various hydraulic parameters for closure gap after computation include upstream and downstream water levels in closure gap, water level along axis of closure dike, drop, diversion volume and ratio for the open diversion channel and mean velocity in central line of the closure gap. Results computerized according to mathematical model and hydraulic model test are basically identical. Difference between diversion volumes of the open diversion channel is less than 5 %, except for individual cases. Upon successful closure of the main channel for the Three Gorges Project, results computerized according to mathematical model and field real measured data are compared, showing that they are basically identical. Difference between real measured and computerized diversion ratios is within 6%.Study on deep-water closure dike nose slump mechanism and its stability is carried out specially in this paper, examples of dike nose slump for computation and forecast are put forward, and slump law is analyzed based on the above study.As a theoretical analysis for closure dike stability, study on slump of dike nose is carried out under the conditions of erosion by current and without current erosion. In condition of no current erosion, the formulas for slump length, height and volume are derived in case of complete slump and the relationship of slump volume varying rate and critical water depth have been further derived, a i...