Earth-rockfill Dam Seismic Strain Analysis And Materials Dynamic Parameters Back-analysis

Earth-rockfill dams are the most commonly constructed type of dams. Most of the high earth-rockfill dams existing or under construction in China are located in areas of high seismic intensity. With the implementation of West China Development strategy and the West-to-East Electricity Transmission project, a new patch of high earth-rockfill dams will be built in the high-intensity areas in Southwest and Northwest China. However, if these dams fail upon the occurrence of earthquakes, disastrous consequences will emerge.Currently, the research on seismic resistance of earth-rockfill dams is far lagged behind engineering practice. Anti-seismic analysis basically depends on the equivalent linearization method proposed in1970s, which is accurate in evaluating the distribution of seismic acceleration and shear stress only under low nonlinearity. The seismic deformation should still be estimated by using semiempirical methods. However, the seismic injury and damages of earth-rockfill dams can still not be reliably predicted. There is no reference for designing of earth-rockfill dams with a height over200m at home and abroad. Currently, because few modern compacted earth-rock dams have undergone earthquakes, there are few records of real seismic reactions or few seismic damage data from high earth-rock dams in high intensity regions. Moreover, because the nonlinear dynamic constitutive models for large-strain dam materials, and the theoretical research on solving methods are immature, it is difficult to obtain the dynamic damage response of high earth-rock dams by using theoretical analysis and numerical calculation, or to clarify their seismic damage mechanism. Therefore, it is hard to accurately evaluate their anti-seismic security under earthquakes. This severely affects the reliability, economy and science in anti-seismic design of high earth-rock dams, and restricts the development of their construction. Therefore, to meet the rapid development of high earth-rock dams in high-intensity regions in China, these key anti-seismic problems should be solved immediately.On account of some key problems in studies about earthquake resistance of earth-rockfill dams, earth core rockfill dam shaking table test, residual strain of Zipingpu Concrete Faced Rockfill Dam (CFRD) after Wenchuan earthquake, and back-analysis of earth-rockfill dam dynamic parameters were carried out. The contents and conclusions are as follows:(1) Based on the data smoothing method which combines the finite element method and general interaction validation, a set of programs suitable for strain measuring and calculation in geotechnical test models were developed. The three point bending beam experiment verifies the correctness and reliability of the programs. This method is applied to the strain measuring and calculation of the earth core rockfill dam shaking table model test, so the displacement field and strain field of model dam were obtained. Meanwhile, the earthquake damage mechanism of core rock-fill dam was discussed. The results show that the failure process can be roughly divided into three stages:overall deformation stage, dam-slope slipping deformation stage, and failure stage. The second stage starts when the overall movement turns to sliding along the upstream and downstream slopes. The failure pattern of the model dam is shallow damage along upstream and downstream slopes under empty reservoir, and is deformation failure along upper downstream slope under full reservoir.(2) Finite element smoothing was used to process the seismic residual deformation data from the Zipingpu CFRD and thereby to obtain permanent deformation displacement fields. Then, the seismic residual strain field was calculated, including vertical seismic residual strain, volumetric strain, shear strain of the dam body, and slope residual strain, which can be used to explain various seismic damages observed on the dam body. Therefore, the method in this study is reliable. The precision of the acquired residual strain satisfies engineering requirements.The results show that the maximum settlement rate on the dam body occurs at about2/3of the dam height, and dilatancy occurs approximately from the dam crest to30m in the upstream and downstream slopes, so this region should be reinforced by anti-seismic measures. The immediate cause of the dislocation of horizontal construction joint in face slabs is the excessive residual shear strain. The two bank abutments are under axial tension; the valley is extruded axially and the entire dam body shrinks to the valley.(3) Real earth-rockfill dam materials dynamic parameters different slightly from that obtain from indoor laboratory test.In order to probe the rationality of current detemination method of earth-rockfill dynamic parameters, two back-analysis methods of earth-rockfill dynamic parameters were presented according to observed seismic acceleration information.①The back-analysis approach of earth-rockfill dynamic parameters based on response spectra and acceleration peak is presented. According to the acceleration response information of Liyutan Dam in the Chi-chi earthquake, the dynamic parameters were obtained by applying the back calculation approach. The results demonstrate that the dynamic shear modulus coefficient K of the dam materials obtained from laboratory dynamic triaxial test is smaller than the true value, suggesting that it should be adjusted.②The back-analysis approach of earth-rockfill dynamic parameters based on earth-rockfill dam dynamic characteristics is presented. According to the acceleration response information of Zipingpu CFRD in the aftershock of Wenchuan earthquake, the dynamic parameters of dam materials were back-analyzed. The results indicate that K of the dam materials obtained from laboratory dynamic triaxial test is smaller than the true value, suggesting that it should be adjusted.