Seismic Response Characteristics Of Asphalt Concrete Core Dam Under Spatial Non-uniform Wave Input

Asphalt concrete core embankment dams have excellent anti-seepage performance,good seismic performance,and strong ability to adapt to large deformations,and are widely built in the western region of China,which is rich in water energy resources.However,the dam site is difficult to avoid the frequent occurrence of strong earthquakes in the western region,and the deep overburden layers of the riverbed,which brings severe challenges to the seismic safety of asphalt concrete core dams.For a large-span hydraulic structure such as an asphalt concrete core wall dam,the spatial non-uniform ground motion of the dam site cannot be ignored.The nonuniform ground motion enhances the dynamic interaction between the foundation and the dam,intensifies the difference in the seismic response of the dam,arouses greater stress in the core wall,and increases the degree of damage of the dam.However,the response characteristics and failure modes of asphalt concrete core wall dams are not clear under the spatial non-uniform ground motion.This paper constructs respectively the non-uniform free fields of elastic halfspace and the nonlinear overburden sites under various waves combination oblique incidence based on the seismic wave combination effect and the wave potential function,develops a viscoelastic artificial boundary element in which the artificial boundary parameters change in real time with the dynamic shear strain of soil,establishes a non-uniform wave input method for halfspace and layered overburden sites under combined waves oblique incidence,carries out the study on the seismic response characteristics of asphalt concrete core wall dams on different sites under spatial non-uniform wave input.The main research contents and conclusions are as follows:(1)The non-uniform free fields of elastic half-space and overburden layers site under different incident modes of seismic waves are constructed.Based on the seismic waves combined effect,the half-space free fields under 3D oblique incidence of plane P-,SV-and SH-waves are constructed.Based on the same principle as the motions of the control point and the design ground motions,the combined oblique incident waves time histories in the bedrock are inverted,and then the half-space free fields under the 2D combined oblique incidence of P-and SV-waves and the 3D combined oblique incidence of P-,SV-and SH-waves are constructed.A method for determining the input ground motion at the bottom of the overburden considering the transmission effect of the bedrock-overburden interface is proposed.Based on the wave potential function,the amplitude matrix in the layered overburden under seismic waves oblique incidence is deduced in frequency.The nonlinear overburden free field under the combined oblique incidence of seismic waves is inverted by IFFT transform and combined with the equivalent linearization method.The results show that the ground motion field of the dam site constructed based on the 3D time-domain inversion model is more comprehensive,and the greater the distance from the control point,the more significant the difference between the site ground motion and the design ground motion.(2)The non-uniform wave input methods for bedrock foundation and overburden layers foundation under single-wave spatial oblique incidence and multi-type waves combination oblique incidence are established.Based on the potential function,the equivalent nodal loads are derived,which can reflect the three-dimensional spatiality of the incident direction of the seismic wave and the difference in the spatial superposition mode,combining with the viscoelastic artificial boundary,the non-uniform wave input methods under the oblique incidence of P-,SVand SH-waves and three kinds of waves combination are established.A viscoelastic artificial boundary element whose damping and elastic coefficients change dynamically with the dynamic shear strain of soil in real time is developed,combined with the free field of the overburden layers,the non-uniform wave input methods of the overburden foundation under the vertical incidence of seismic waves and the oblique incidence of seismic waves are established.The results show that the method has high computational accuracy.(3)The response characteristics of asphalt concrete core wall dam on bedrock foundation under non-uniform wave input are studied.The formation mechanism of spatially varying ground motions of the valley surface is revealed.The mechanism of the significant difference in acceleration and dynamic stress between the wave-facing and the wave-backing sides of the core wall is revealed.A new method for evaluating the tensile safety of the core wall was proposed,and the weak parts of the core wall were identified.The element seismic safety factor of the dam body is introduced,and the local dynamic stability of the dam body is evaluated.The results show that compared with the seismic waves vertical incidence,the non-uniform ground motion caused by the single-wave spatial oblique incidence causes the maximum and minimum principal stresses of the core wall to surge,the maximum increase is 14 times,which is prone to local tensile failure on the back wave side of the core wall.The principal stresses caused by the 3D combination oblique incidence of P-,SV-and SH-waves are larger under the same design ground motion intensity,with a maximum increase of 32%.Non-uniform ground motion has a significant impact on the response and seismic safety of asphalt concrete core dams,which should be considered in seismic design.(4)The dynamic interaction mechanism between the deep overburden layers and the asphalt concrete core embankment dam is revealed.The high precision of nonlinear wave input under vertical incidence of seismic waves proposed in this paper is demonstrated.The influence law of the influence factors of the transmission effect of the bedrock-overburden interface on the acceleration of the core wall dam is clarified.The mechanism of the significant attenuation of ground motion at the dam-foundation interface due to the dynamic interaction between the overburden layers and the core wall dam is revealed.The effects of the incident angle and the ground motion input methods on the dislocation between the transition material and the core wall,the stress of the core wall and the seismic subsidence of the dam body are analyzed.The results show that with the increase of the incident angle,the vertical dislocation and horizontal detachment,the stress of the core wall and the seismic subsidence of the dam body increase.Compared with the non-uniform wave input,the dam body response was significantly overestimated under the uniform input.The horizontal detachment and vertical dislocation increase by 2.23 times and 1.23 times,respectively.The core wall is prone to tensile failure in the middle,and the vertical seismic subsidence of the dam body increases by nearly 20%.