| A lot of high earth and rock dams have been constructed or being planned or designed in the western region of China (meizoseismal area). With advantages in safety, economy and adaptability, Concrete Face Rockfill Dams (CFRD) are selected as one of the most widely used rockfill dam types. Many of these high CFRDs located at valleys with extremely complex geological conditions, and at regions where earthquake with high seismic intensity occurred frequently. Therefore, it has great theoretical practical significances to study the aseismic measures of high CFRDs to survive from strong earthquakes.A large earthquake (Ms=8.0) occurred on May12,2008in Wenchuan in China's Sichuan province,17km west from where locates Zipingpu CFRD. The largest seismic intensity in the epicenter was up to XI. The strong shock caused obvious damages on Zipingpu dam. Unfortunately the rock station under Zippingpu dam failed to capture the base rock seismic wave of Zippingpu dam during Wenchuan earthquake. Thus the damages from field investigations cannot be used to quantitatively verify the results predicted by dynamic numerical analysis. Equivalent linear viscoelastic model was usually applied in dynamic constitutive model of rockfill materials. Therefore, the elastic-plastic analysis method was established for the stress-strain behavior of high earth and rockfill dam. It is a great significance to calculate the process of gradual deformation during earthquake.The present research is supported by the Natural Science Foundation of China "Study on aseismic measures of high earth and rockfill dam in meizoseismal area"(No.50679093), the National Mega-project of Natural Science Foundation of China "Disaster simulation and safety control of high earth and rock dams during earthquake"(No.90815024) and the National Key Technology R&D Program for the11th5-year plan "Study on earthquake damage assessment of Zipingpu reservoir and aseismic technology of dams"(No.2009BAK56B02). The deformation of Zipingpu dam and the dislocations of face slabs at horizontal construction joints were simulated by numerical method. A elasto-plastic model for static and dynamic analyses on high rockfill dams was developed and verified. The main contents of this study are as follows:(1) The peak acceleration and spectrum characteristic of the dynamic responses of Zipingpu CFRD shaken by aftershocks after Wenchuan Earthquake were analyzed. Several representative motion records captured by the rock stations at the dam site were selected to generate the seismic input for three-dimensional dynamic finite element (FE) analysis of Zipingpu CFRD. The calculated acceleration responses were compared with the measured data at different levels. The characteristic of dynamic response of the dam under small earthquake was studied.(2) Selection of the seismic wave input of Zipingpu CFRD in dynamic simulation under Wenchuan earthquake was discussed at first in this paper.3-D dynamic FE simulations of Zipingpu CFRD were carried out with various seismic input waves, including records of main shock captured by nearby rock stations, records of aftershocks captured by stations on the dam site, and the artificially derived seismic input according to the standardized spectrum of specifications for seismic design of hydraulic structures. The dynamic responses of the dam under various seismic input waves are compared with the measured data. Suitable seismic wave inputs of Zipingpu CFRD under Wenchuan earthquake such as seismic waves measured by Diban station of Mao town and artificial seismic waves generated by standardized spectrum were suggested for dynamic simulation.(3) The damages of Zipingpu dam during Wenchuan earthquake were simulated numerically. Three-dimensional FE methods, respectively based on strain potentials and rigid sliding method, were adopted to calculate the permanent deformation of the dam and further to calculate the dislocations of face slabs between the second and third construction stages. The calculated results are compared with the field measured data. The major factors affecting the dislocation of face slabs, including the direction of the joints, water level of the reservoir and different seismic inputs, were analyzed.(4) An elasto-plastic model for static and dynamic FE analyses of high CFRD was developed based on the generalized plastic P-Z model. The elastic shear modulus, elastic bulk modulus, loading and unloading plastic modulus, and and reload function about stress history were modified according to the stress-related behaviour and the damping characteristic of rockfill materials. The parameters of the improved model were determined by large-scale static and dynamic triaxial experiments. The improved generalized plastic P-Z model was successfully programmed into the FE software GEODYNA. Static and dynamic analyses of Zipingpu dam were carried out using this elasto-plastic model. The dam deformation during construction and during the earthquake, and the dislocations of face slabs between construction stages during the earthquake were calculated.(5) Comprehensive aseismic measures for improving the stresses distributions of face slabs were proposed, including adopting extrusion-sidewall technology during construction, reducing the friction factor between sidewalls and face slabs, and adopting optimization scheme in the filling materials between vertical joints. The stress distribution behaviour of face slabs of high CFRD before, during and after earthquake were investigated by3-D staic and dynamic FE analyses. The effects of various dam height and valley shape were also discussed. The results of FE analyses showed that the above aseismic measures can effectively improve the stress distribution of the face slabs of CFRDs.
|
PDF Full Text Request