Research On The Hydrodynamic Pressures And The Mechanisms Of Air-Cushion Isolation Of High-Dams

The interaction between dam and reservoir systems during earthquakes is an important disciplinary for the earthquake-resistance design of hydraulic structures. Recently, research focus has concentrated on the interaction of dam-reservoir-foundation system. Difficulties existing in this research are the interaction of dam-reservoir system and/or the couplings between the fluid and the solid, namely the hydrodynamic pressures. Hydrodynamic pressures can be an important cause of dam failure, especially, for high-dams. For antiseismic design, understanding the characteristics of hydrodynamic pressure distribution has a great importance so that safety measures to reduce the earthquake effects can be taken accordingly. In this study, therefore, combining with the project aided by the National Natural Science Fundation of China (No.50379029) and concentrating on the dynamic test, a series of mathematic and mechanical theories are used to investigate profoundly the mechanism of interactions among the dam-foundation-reservoir and air-cushion systems for the air-cushion isolation of gravity dam, and the dynamic test design on the air-cushion isolation of high arch-dam is preformed. Some new ideas and methodologies have been proposed. Detailed results of the research are as follows: 1.Experimental test using the large-scale shaking table for the gravity dam-reservoir-air system has been performed for the first time. The therotical analysis and numerical simulation results on air-cushion isolation for high-dam earthquake-resistance have been tested. The mechanisms of air-cushion isolation for dam earthquake control and some key points of earthquake-resistance design have been disclosed by dynamic test. Results on hydrodynamic pressures from this experiment agree well with numerical simulations for the anti-seismic effect of air-cushion isolation. Furthermore, the scientific meaning and application prospect of the air-cushion isolations for high-dam earthquake control have been effectively tested. 2. Based on the theory of dynamic similarity on physical model test, similarity analysis has been done for gravity dam-reservoir-air system. Due to the working mechanism and characteristic of the air-cushion, some key factors of the system and main similarity requirement are considered, a normal-model of geometry similarity is applied for dam-reservoir -foundation system, while approximate similarity requirements of geometry for air cushion isolation system are exerted for the conveniences of test. In order to assure the accuracy of experiment test and the technical measures of the model production, several alternatives of model scales are selected. A comparatively preferable model scale has been screened out on the basis of technical feasibility and economical rationality for Longtan gravity dam-reservior-air system. 3. According to the similarity specialty, proportion and mechanics specialty of model material, similarity relations derived in this study are employed for the selection of emulation material ratios though repeatedly adjusting and testing on small samples of dam-reservoir-gas system. These emulation material ratios must meet the requirements of similarity relations of the large-scale oscillation experimental equipment. Finally, a satisfactory mixture ratio, the structure of air compartment, test scheme and technical measures meeting similarity relations of gravity dam is obtained. And then, the test results is obtained, the test record is rational and credible on the whole. 4. The applicability of the non-linear dynamic FEM numerical model and method has been checked by the results of dynamic model test on the large-scale shaking table, this provided some calculational method and analysis measures for the study and applications of the air-cushion isolation technique of dams. 5. Based on the experimental test on large-scale shaking table for the gravity dam-reservoir-air system, the numerical simulation of the arch dam-foundation-reservoir-air system has been done, and the similarity relation of the system has beenconfirmed. a satisfactory mixture ratio meeting similarity relations of arch-dam and its foundation is obtained. Based on these works, model design on the large-scale oscillation experimental equipment is carried out regarding the arch dam-foundation-reservoir-air system. Briefly, in order to evaluate the anti-seismic effects of air cushion isolation, dynamic model test on large-scale shaking table for the gravity dam-reservoir-air system has been performed for the first time.The test results and numerical simulations show that air isolations will reduce the hydrodynamic pressures significantly and restrain the vibrations of dams in earthquake. If the dam and reservoir is isolated by air cushions, the shortages of hydrodynamic pressures will be more than 65% for gravity dam. So the air-cushion has good isolation effects, and it has important scientific meaning and effective value. Therefore, this technique of air cushion isolations can be widely applied into hydraulic dams to ensure great safeties.