Research On Mechanism And Numerical Simulation Method Of Seepage Failure Of Dike Foundation

Dike is the world’s oldest flood control engineering measures. And it is the last line of flood protection. The importance of dike engineering is self-evident. Seepage failure, in the past and for the foreseeable years, was and will be the most direct and biggest threaten to the dike. Although the research on seepage failure made a little progress, the general law of seepage failure is still not enough to be recognized. To improve the awareness of seepage failure of double-layers foundation of dike, the following jobs are carried out in this dissertation:1. Research on the experimental technique of model test. According to the characteristics of double-layer of dike foundation, the test apparatus is designed and the method is studied. The scales of model test are analyzed.In view of the lack research on the impact of overburden layer on the development of seepage failure, the nature of contact between the different simulating materials and sand is emphatically analyzed. According to the test results, the effection of the covering layer is not only impervious. The stress effection is also not neglected.Considering the seepage exit as the necessary condition of seepage failure, how to simulate the weak spots of the overburden layer is studied. By changing the ratio of compositions, the characteristic of overburden layer is controlled.2.Experimental research on the seepage failure.1) Experimantal study on the formation of seepage exitBy changing the size of the weak spot of the overburden layer, the general law is studied on the formation of seepage exit. Also the effection of the properties and the thickness of the covering layer on the formation of seepage exit are researched.2) Experimatal research on the development of seepage failureFirst, using cement mortar as the covering layers, progress of the seepage exit and concentrated seepage channel are analyzed. Secondly, results of experiments, using the bentonite and seal flexible water bag as the overburden layer, are compared. The effection of overburden layer on the seepage failure is analyzed.3. Research on the mechanism of seepage failure Based on the experimental results, the mechanism of formation of seepage exit is analyzed. It is pointed out that the seepage exit is the necessary condition of seepage failure.According to the results of experiments on the development of seepage failure, the influence of the inner factors on the seepage failure is studied. It is put forward that the final failure model of seepage failue is flow soil. The development of concentrated channel is the result of interaction between the anti-permeability of soil and seepage strength. Based on understanding of the seepage failure mechanism, two criterions are derivate. One is the stress strength, considering the seepage force. The other is the limited balance of the rotational moments of soil particle.Considering the failure zone is lesser, Darcy law is still satisfied on the most of the region. Meanwhile the relationship between the water head and flow is available throught the hydraulic method.4. Research on numerical simulation1) Numerical simulation on the progress of seepage faiure Based on understanding of seepage failure mechanism, the seepage field is computed by axisymmetric FEM. Compared the results between the experiment and numerical simulation, the above research method and two criterions on the seepage failure are reasonable, feasible.By applying of above program on the simulation of seepage failure, the precise definition of“harmless piping" is put forward.2) Numerical simulation of seepage exit formationAccording to the experimental observation and analysis, the formation of seepage exit is result of cracking and expansion. Based the theory of fracture machanics, the formation of seepage exit may be simulated by the extended finite element method. And on the basis of the references, the program of linear elastic 2-D extended finite element is developed. Compared the results between the experiment and numerical simulation, the above research method are reasonable, feasible.