Experimental Research On Seismic Damage Mechanism Of High RCC Arch Dam

With the vigorous development of China's water conservancy, a large number of arch dams have been found or being in construction. So, to study the seismic responses of arch dams will be very important to seismic design and seismic safety. High Roller Compacted Concrete (RCC) arch dams under strong earthquakes have complex failure mechanism, and are affected by many factors. Shaking table tests has become the effective way to study the earthquake responses of arch dams. Meanwhile, in accordance with "Code for Seismic Design of Hydraulic Structures of Hydropower Project" (NB 35047-2015), hydraulic structures which the intensity of an earthquake resistance is VIII and above, height of over 150 meters, engineering seismic fortification category Group A, are asked to test research on dynamic models. The study of model materials, simulation and measurement technology about high dams dynamic model tests is not perfect yet. There are still many challenges for researchers to study the seismic response of arch dams, such as nonlinear behavior of structural joints, the role of horizontal weak layer, and the dam-reservoir interaction. In order to study these critical issues, this paper conducted a series of studies, including the experimental research of model materials, the technical methods to monitor damage, and the destruction shaking table tests. The main contents are as follows:(1)The present work has developed a high density, low elastic modulus, low tensile strength and good brittleness dam model material. This work provided uniaxial tension and compression constitutive relation of model material based on a series of tests at different strain rates. Based on the tests, the stress-strain curve is obtained and rate-dependent empirical formulas for strength, strain at peak stress and the elastic modulus of the model material is given respectively. The relationship between Poisson's ratio, energy absorption capacity, failure pattern and strain rate is analyzed. Model material properties mentioned above is also compared with the prototype material. This work not only provides the material study for dam dynamic model tests, but also provides material parameters for numerical study.(2)The present work has developed a novel seismic damage monitoring method to achieve the dynamic stress history monitoring perform and internal damage monitoring for dam model. Before dam model tests, sensors' calibration tests were carried out by the use of piezoelectric effect under different loading rates. Through the preliminary experiments to verify the effective of damage monitoring method, and damage index was defined by RMS index. A dam model system with a distributed PZT sensors was used as an object for verification. This proposed method can complement each other with the traditional method to improve the measurement accuracy of dam dynamic model test.(3)Based on the model materials research and damage monitoring technology research, some different dynamic rupture tests was carried out to study the impact of structural joints and horizontal weak layer on damage mechanism of RCC arch dam. The establishment of the model was based on elasticity-gravity similarity law, the design of dam model takes into account the rate sensitivity of the mechanical properties of materials. The simulation of contraction joints took the effect of key grooves into consideration, while the simulation of induced joints was based on fracture mechanics. In order to provide the material properties information, several groups of splitting tensile test which containing a weak layer were carried out under dynamic loading. The results showed the opening of contraction joints and induced joints released the stress on corresponding position, and then mitigated the damage of the dam. The presence of weak layer mainly affects the dam failure mode, but does not significantly reduce the overall overload capacity of the dam structure. The physical simulation technology is helpful to understand the effect of joints and weak layers on seismic damage mechanism and provide some useful information for the seismic design of RCC arch dams.(4)In order to study the dynamic response of arch dam and failure modes under the influence of reservoir, arch dynamic model test was conducted in this paper. By comparing the results with or without reservoir, it was discovered that the reservoir can keep the arch dam in prelaoding state and give full play to the characteristics of arch compression capability. Considering the similitude and the actual conditions, the influence of the density of reservoir was studied by the numerical simulation. The concrete damage mechanics was chosen for the nonlinear constitutive model of the dam. Material parameters were obtained through the mechanical performance tests of model material. The cohesive elements was selected to simulate the structural joints.The numerical model was checked by the model test. Numerical results showed that the density of reservoir mainly affect the distribution of maximum tensile stresses for upstream face, and the failure mode can be ignored. This method using natural water to simulate reservoir is an effective way in the current circumstances.