Shaking Table Model Tests Study On Seismic Failure Mechanism Of Earth-Rockfill Dams

The energe demand is still a key topic of the present world. The latest five year energe plan of China proposes that we should accelerate promote the development of the water resourses. The earth-rockfill dam is the mostly used dam type in the construction of the dam engineering. An increasing number of tall earth-rockfill dams will be built in southwest China and other locations around the world, some of which are highly seismic areas. The height of the dam is more and more high, and the issue of safety of them becomes of vital importance. The safety of the earth-rockfill under strong earthquake is the key problem of the hydraulic engineering and it will be a disastrous accident if the earth-rockfill is broken. However, only a limited number of dams have been damaged by earthquakes, particularly earthquakes with high magnitude. This lack of data limits the accuracy to judge the seismic safety of earth-rockfill dams under high-magnitude earthquakes. So the dams’ failure mechanism during earthquakes has remained unclear, which has limited the ability to accurately judge dam safety. The current aseismic measures mostly according to the experience and lacking of the validation of the actual projects or experiments. So researches on the seismic failure mechanism and aseismic measures of earth-rockfill dams have important significance on improving the design technology and protecting the life security of the public people.It is difficult to predict the deformation of the earth-rockfill due to the lack of the in-situ data and the soil complexity in both the constitutive model and calculation parameters. The shaking table model test is the most effective method for studying the failure mode and the failure mechanism of soil structures under seismic loads because of its flexibility and convenience. The rockfill has strong nonlinear characteristics so it is hard to select a model material satisfying the similitude law completely in the earth-rockfill dam shaking table model tests. In addition, the current experimental technologies have some limitations on researching the seismic failure mode and failure mechanism of the earth-rockfill dams such as it is hard to measure the displacements of the discrete material and it is also hard to measure the strain of the model slab and clay core with low strehgth and elastic modulus. So the researches on the model similarity, the development of the model material and the improments on the experimental technologies have great significance on improving the technical level of the shaking table model test of earth-rockfill. And the solving of these problems is also important on evaluating the test results and applying the test results on the practical project.Considering of the limitations of the current experimental technologies, some improvements on the shaking table model test technology are introduced. And then, the seismic failure mechanism and aseismic measures of earth-rockfill dams (including earth-core rockfill dam-ECRD and concreted faced rockfill dam-CFRD) are researched based on the introduced experimental technologies. The research work carried out in the present thesis can be summarized as follows:1) A model slab material satisfying the similitude law is developed according to numerous experimental datas. The PIV technology is applied to large-scale shaking table model tests on slope stability, and the failure criterion is also studied. A system for image collecting, fast storing and pattern recognition, by which Particle Image Velocimetry (PIV) technology can be used in shaking table tests to obtain the displacements of soil particles. A type of specially designed distributed Fiber Bragg gratings (FBG) as strain sensors to measure the strains of the model slabs which have very low elastic modulus and strength. The disturbance of the FBG sensors to the dam model are reduced by linking the sensors together and several sensors can be measured together by a single channel. These new experimental technologies provide technician support to research the failure mechanism of earth-rockfill dams under earthquake.2) The methods to prepare the model materials are discussed, and some examples are analyzed. A series of model experiments are designed to investigate the dynamic failure mode and failure mechanism of ECRDs. Different input waves including the gradually increasing sinusoidal waveform and a series of synthetic wave with increasing magnitude are employed to investigate the failure mechanism of ECRDs under different conditions. Then the effectivenesses of the developed experimental technologies are validated according to the test results.3) A series of model experiments are designed to investigate the dynamic failure mode and failure mechanism of CFRDs. Based on the experimental results and numerical simulation, the failure process of the dam and the failure mechanisms of slab fracture and slab dislocation are discussed.4) A shaking table model test is designed to research the main damage characteristics of the Zipingpu dam, i.e. the slab dislocation. And the failure mechanism of the slab dislocation is researched by the test results, the numerical simulation results (including the finite difference method and the dynamic finite element time history method), and also the analysis method resluts. 5) To discuss the effects of possible measures on enhancing the stability of CFRD, a series of model experiments are conducted. The measures discussed herein include using geo-textile to enhance the upper model, placing some slope protection materials on the downstream slope surface, and replacing the top model rock-fill by cemented rock-fill material. Moreover, a new aseismic measure is presented to overcome the weakness of the current measures that is using the concrete layer to replace the geo-textile and the steel bar. Accroding to the comparison of the crest settlement rate, the surface grain yield acceleration, the slab fracture acceleration, and the slab dislocation acceleration of each model, the effectiveness of each aseismic measures on improving the stability and anti-deformation ability of CFRD are researched. Finally, the measure in which firstly the upper1/5of the dam is reinforced, and then the downstream slope is protected by the slope protection material, such as grouted stone pitching, is suggested.This work is funded by the National Natural Scientific Foundations of China (Grant No.90815024,51121005,50978045and2009T017). These supports are gratefully acknowledged.