Research On Mechanism Of Emergence And Expansion Of Seepage Failure Of Dike Foundation

Double-layer dike foundation widely distributed in the middle and lower reaches ofrivers. Seepage failure is the most common failure modes in the dike foundation. In recentyears, many scholars have done a lot of research on the seepage failure generation condition.But few research on how the piping channel developing after the seepage exit generating. Thedevelopment of the piping channel is related to the degree of risk. For this problem, this paperstudies the characteristics of the piping channel. After the seepage exit appears, thedevelopment of the piping channel contains two parts: the radial expansion and the axialexpansion. This paper do the flowing jobs in the problem.1. Research on the mechanism of piping channel development, contains radial expansionand axial expansion. About the radial expansion, take the particles on the side wall as theresearch object. The final form of the channel radial expansion is determined by state of theseparticles. River Dynamics concepts and formulas introduced in the mechanical analysis.Incipient velocity of particles was deduced by the particles stress analysis. Interactionsbetween particles of different size and incipient standard were considered in the analysis.Considering the impact of turbulent flow, non-uniform velocity distribution and flowcharacteristics in the channel, channel average velocity were used as channel radial expansioncriteria.2. Research on the experiment of piping channel development, contains radial expansionand axial expansion. About the radial expansion, took multi-group experiments by using twomodel box. Experimental results demonstrate the impact of the hydraulic gradient to the radialexpansion is great when the head difference between the channel and the remote is low. Andwhen the head difference is high, the impact becomes not so clear. At this time, the impact ofthe scour in the channel is clear. About the axial expansion, took multi-group experiments byusing two typeset of material to simulate the aquitard. The shape changes of the channel werestudied in plan and section. Experimental results confirmed the thesis of the tip hydraulicgradient trend.3. Research on the numerical of piping channel development, contains radial expansionand axial expansion. About the radial expansion, prepared a two-dimensional finite elementprogram. The program simulated the channel radial expansion process. The channel averagevelocity, natural angle of repose and additional shape conditions is the determinationcondition of the radial expansion. The head difference between the channel and the remoteand the flow in the channel is the boundary conditions. About the axial expansion, proposed a method of equivalent substitution based on the Multi-layer High permeableThree-dimensional finite element program. This method can achieve accuracy and reduce theamount of computation. When it came to judge the channel radial expansion, the actual formof the channel cross-section was used. When it came to calculate of seepage field, theequivalent rectangular cross-section was used. The flow in the channel and the seepage fieldout the channel is consistent with both before and after the change. The seepage field and thehydraulic gradient in channel tip can be get from the program. They can used to judgewhether the channel will occur axial expansion.4. Verify the correctness of the mechanismand the program by comparing the results of the calculation and experiment. Discussing thedevelopment of the piping channel in the typical double-layer dike foundation based on thefinite element program.