| Summary: | 碩士 === 國立中興大學 === 水土保持學系所 === 105 === Landslide dam breach releases large amount of water and sediments, which cause dramatic changes at the downstream channels and it poses significant risk to residents and properties located in the inundated area. Field experiments on dam failure were conducted to observe the breaching process. These were conducted on November 7, 2016 (Test 1) and April 24, 2017 (test 2) into two field experiments, test 1 is less compaction case and test 2 is a natural compaction case. This research used intrusive instruments such as pressure gauge, soil moisture sensor and Acoustic Doppler Current Profiler (ADCP). This study is a first of its kind that 3D-PTV was applied in the field dam failure. In addition, the dam subsidence and flow field of the cross section were quantified by a nonintrusive method — 3D coordinate translation analysis. Direct observation of the dam breach included; 1. The relationship between dam subsidence and the water content inside the dam during the period of impoundment 2. The change of the surface flow field during the breach period.
It is found that compaction has a significant effect on the breach type and hydrograph. The piping will occur at the downstream slope when the dam is less compacted and when impounded time is long. In the impoundment stage, compaction and the height of groundwater are the most influencing factors. In the seepage stage, the most significant factor is compaction and impounded volume. Through the 3D image analysis, the dam subsidence follow a linear trend. In addition, compaction affects the dam subsidence, but does not affect the horizontal displacement, and the crest and the region of weak structure have large subsidence. The study also revealed that the vertical velocity played an important role in surface velocity, the proportion is about 32%, which indicated that previously applied 2D-PTV or LSPIV is not applicable in the breach channel. Finally, the average velocity distribution is divided into three stages. During the first stage, there is flood down cut, discharge and velocity increase. In the second stage, lateral erosion occur, discharge remain constantly high and increases slowly to peak and velocity decreases. Finally, during the third stage, flood begins to head cut, discharge decreases and velocity increases slowly to constant value. The results show that the application of this technique can improve the accuracy in the dam breach process.
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