| With the rapid improvement of high dam construction technology in China,the construction of earth-rock dam has reached 300 m level.The size of the high earth-rock dam is huge,and the length of the dam-foundation interface along the river is more than kilometers,and the elevation of the riverbed connected with the dam is hundreds of meters different from that of the two banks,which makes the ground motion input on the dam foundation surface have very obvious inconsistency.During the earthquake,the scattered waves inside and outside the dam body will transmit more energy to the foundation and then radiate to the infinite domain,which will intensify the influence of the dam foundation interaction on the dynamic response of the high earth-rock dam.In addition,most of the current seismic response analysis of high earth-rock dams assumes that the seismic wave is vertically incident.However,in the actual earthquake,there will be oblique incident earthquake wave,and there will be obvious traveling wave effect on the dam foundation interface when the local seismic wave is oblique incident.These factors which have important influence on seismic response of high earth rockfill dam have not been well considered in the current calculation and analysis.However,the construction of high earth-rock dams in China is mainly distributed in the southwest areas with high earthquake intensity and difficult to avoid.Once the dam is wrecked by a strong earthquake,it will greatly damage the safety of people’s lives and property.Therefore,the reasonable ground motion input should be paid more attention to in the seismic safety analysis of high earth-rock dams.At present,static and dynamic calculation parameters of earth-rock dam are generally determined by laboratory static and dynamic triaxial tests.However,the laboratory test is limited by equipment conditions,so only the scale material test can be carried out.There is a big difference between the mechanical parameters of the scale material obtained and the field full-scale material.In the static analysis of earth-rock dams,the settlement of the scale material parameter calculation existing the problem of "high dam is small".The dynamic parameters,which play a key role in seismic dynamic response analysis,also have scaling effect in the test results.Therefore,to obtain the reasonable dynamic parameters of the prototype full-scale rockfill becomes the premise of improving the seismic response analysis.In order to solve the above problems,this paper has carried out the seismic input research of the interaction of high earth-rock dam-foundation-river valley,back analysis of dynamic parameters of rockfill materials considering the interaction,identification of modal parameters of high earth-rock dams,and seismic safety of high earth-rock dams when seismic waves are incident obliquely in different directions and other research work.The main research contents and conclusions are as follows:(1)By constructing two-dimensional and three-dimensional uniform viscoelastic artificial boundary elements and combining with the method of equivalent load node force,the input method of vertical incidence of ground motion in two-dimensional and three-dimensional complex site is established.This method can better simulate the radiation damping effect of the infinite foundation,and can also consider the nonlinear characteristics of the foundation,and can simulate the seismic wave propagation process and the inconsistent ground motion input caused by the valley topography.A typical dynamic calculation example of a high earth-rockfill dam shows that when considering the dynamic interaction between high earth-rockfill dam,foundation and river valley,the extreme value of the dam response decreases obviously,and the traditional consistent ground motion input method often overestimates the seismic response of the dam,thus underestimating the ultimate seismic capacity of the dam.(2)Based on the input method of two-dimensional and three-dimensional vertical incidence of ground motion,and using the ground motion information measured at the dam monitoring point during earthquake,two methods for dynamic parameter inversion of rockfill are presented,so as to discuss the rationality of the current determination method of dynamic parameters of indoor and outdoor dam material.Based on the developed 2D viscoelastic artificial boundary and its corresponding ground motion input method,the multi-population genetic algorithm and radial basis neural network were used to construct the inversion platform.A dynamic parameter inversion analysis model of earth-rock dam was proposed considering the interaction between dam foundation and radiation damping.Based on the main seismic records of the Chichi earthquake,the dynamic parameters of Liyutan Dam are analyzed and compared with the results of rigid boundary inversion and indoor and outdoor tests.It is shown that the dynamic shear modulus coefficient C obtained from the rigid foundation model and the laboratory tests are both small.Using the developed 3D viscoelastic artificial boundary and transfer function method,the problem of ground motion inversion input for river valley topography is solved.Based on the combination of multi-output support vector machine(MSVM)model and particle swarm optimization algorithm,a dynamic parameter inversion method for high earth-rockfill dam considering the interaction effect in 3D river valley topography under weak earthquake is proposed.Based on the Jinggu seismic records,the measuring points in the 3D free valley field were taken as the control points of seismic response.Based on the transfer function and viscoelastic artificial boundary,the ground motion input at the bottom of the model was determined.The dynamic parameters of Nuozhadu Dam were analyzed by inversion.The results show that the MSVM model only needs relatively few samples and training times on the premise of ensuring the calculation accuracy,which can effectively save the time of finite element calculation.By comparing with the inversion results of rigid foundation and laboratory test results,it is shown that the dynamic shear modulus coefficient of rockfill material obtained from the rigid foundation model and laboratory test is small.For the same type of dam materials,the dynamic shear modulus coefficient of upstream rockfill materials is smaller than that of downstream rockfill materials.(3)Based on seismic monitoring data of high earth-rock dams,an automatic identification method for modal parameters of high earth-rock dams is proposed based on covariance-driven stochastic subspace model,improved stability diagram and spectral clustering.Based on the monitoring data of Nuozhadu Dam during the Jinggu earthquake,the frequency and damping ratio of the dam can be well identified by this method.Based on the combination of modal parameter identification method and multi-population genetic algorithm,a dynamic parameter correction method for high earth-rock dam based on modal identification is proposed.The method is applied to the dynamic parameter inversion of the FEM of Liyutan Dam.It is found that the modal parameters of Liyutan Dam calculated according to the laboratory test parameters are quite different from those obtained from the actual weak earthquake records,and the modal parameters corresponding to the inversion parameters are more consistent with the reality.The dynamic parameters of dam inversion are used for seismic response analysis under strong earthquake,and the calculated acceleration of monitoring point is in good agreement with the measured acceleration.Compared with the dynamic shear modulus coefficient of rockfill,the coefficient obtained from laboratory test is small.(4)In the FE calculation,using 3D viscoelastic artificial boundary,considering the oblique incident seismic waves at arbitrary angles in the horizontal plane and the vertical plane,the input formulas for the oblique incident seismic wave of P wave and SV wave at arbitrary angles in the homogeneous field of 3D half space are derived.According to the seismogenic structure in the main potential source area of Nuozhadu Dam site area,the corresponding field response spectrum is determined,the corresponding artificial seismic wave is generated,and the seismic response law of Nuozhadu Dam under the oblique incidence of seismic wave in the main potential source area is discussed.The results show that when P wave and SV wave are oblique incident,the traveling wave effect will be obviously enhanced,which makes the seismic response of the dam have some differences. |
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