Research On Overtopping Breaching Of Geotextile-Reinforced Dams

In order to use the abundant water resources, China has built tens of thousands of reservoir dams. A series of high dams have been built up with the height of 100 m or more. Seismic strengthening with geotextile or steel bar in dam crest has become an important measure in engineering. Historical experience shows that embankment dams are prone to encountering an overtopping breaching failure. For now, the study of dam breaching is not enough, especially the research on reinforced embankment dams has not been reported.In this paper, experimental and numerical simulation methods are taken to study the process and mechanisms of reinforced embankment dam during an overtopping breaching. The main research contents are as follows: a circulating water tank system is developed to conduct model tests of dam breaching. By providing the U-bend in the side of the tank, the channel flow is transformed into a pipe flow, so that an electromagnetic flow meter can be used for measuring dam overtopping flow accurately. The work system, energy dissipation system and flow measurement system are all integrated into the circulating water tank system; 13 groups of small scale model tests are conducted in the tank to study the dam breaching process; Based on the experimental data, the breach vertical-cutting rate function is derived; The PFC(particle flow code) software is used to study the performance of soil with different clay in it; Penetration is considered during an overtopping breaching by using the discrete element method; A half trapezoidal breach numerical model is established to research the extended mode of breach sidewall. The main conclusions are as follows:(1) The performance of the vertical anti-erosion is improved because of the crest reinforcement. The drag force applied by the geotextile causes numerous breach sidewall collapse. The effective reinforced area locates in the 35%-50% range of dam height by analyzing the discharge curve. Reducing the reinforced spacing can enhance the anti-erosion ability.(2) Fitting the discharge curve with the peak flow as the discontinuous point. Before reaching the peak flow, vertical-cutting rate is a power function of time; After the peak flow, vertical-cutting rate is an exponential function of time.(3) Discrete element numerical simulation results show that the curve about erosion rate and fluid pressure transform from straight to concave line gradually with the bond strength increasing; When overtopping water is very shallow, water pressure is lower, seepage of earthen dam is very small. When the overtopping flow grow deeper, water pressure become larger, and the influence of earthen dam seepage could not be ignored. The depth of the breach has a greater impact on breach extension than the breach sidewall slope.