Study On Ground Motion Characteristics And Wave Input Of Valley Site Based On IBIEM

The scattering effect of local topography makes the ground motion field of the valley site extremely complex,forming a significant spatial inconsistency excitation of the large-span buildings on it At present,the influence mechanism of the scattering effect of the valley topography on the ground motion characteristics of the site is still unclear,and it is urgent to establish a spatially non-uniform fluctuation input method for the valley site that considers the scattering effect.Based on the Indirect Boundary Integral Equation Method(IBIEM),this paper analyzes the free field,scattered field and total field solution of the valley site in the frequency and time domains.The influence mechanism of,incident angle and incident wave frequency on the ground motion characteristics of the valley site was proposed,and a wave input method considering the valley scattering effect was proposed.The law of influence of the response.The main research contents are as follows:(1)Based on the IBIEM method,the frequency domain and domain solutions of the total field of the valley site under oblique incidence of P-wave or SV-wave are derived.According to the theory of seismic wave field decomposition and superposition,the total ground motion field of the valley site is decomposed into free field and scattered field.Based on seismic wave propagation theory and boundary conditions,the free field in half space under oblique incidence conditions of P and SV is obtained.Based on the Green’s functions of the full-space compression wave source and the shear wave source,the Green’s functions under the action of the half-space compression wave source and the shear wave source are deduced.Combined with the relationship between the free field and the scattered field on the boundary,the amplitude coefficient matrix of the scattering source is solved.After Fourier transform and inverse transform,the time domain solution of the ground motion response of the valley site is given.The correctness of the IBIEM method is verified by a numerical example,and the convergence and accuracy of the IBIEM method are discussed.(2)The ground motion characteristics of the valley site under the oblique incidence of P-waves are analyzed,and the input method of the fluctuations of the oblique-incidence of P-waves based on IBIEM is established.Based on the IBIEM method,the influence law of the valley slope,the incident angle of P wave and the predominant frequency of incident wave on the peak displacement of the valley surface in two directions is studied.Based on the deviation of the viscoelastic boundary free field input method in calculating the valley scattering problem,a spatially non-uniform P-wave fluctuation input method considering the valley scattering effect is proposed based on IBIEM.The results show that the two-way peak displacement on the wave-facing side of the valley surface is significantly larger than that on the back-quilt side,and the shielding effect of the valley on the seismic wave makes the site ground motion non-uniform;The seismic wave frequency and other factors have a significant influence;with the increase of the incident wave frequency,the difference between the free field and the total field of the two-direction displacement on the truncated boundary becomes larger and larger.The total field input method based on the viscoelastic boundary is basically consistent with the IBIEM calculation results.Field input errors are obvious.(3)The ground motion characteristics of the valley site under the oblique incidence of SV waves are analyzed,and an input method of SV wave oblique incidence fluctuations based on IBIEM is established.Based on the IBIEM method,the influence law of valley slope,SV wave incident angle,and SV wave predominant frequency on the peak displacement of the valley surface in two directions was studied,and the vibration trajectory,displacement time history and main influencing factors of typical characteristic points on the valley surface were analyzed.A spatially non-uniform fluctuation input method for SV waves considering valley scattering effects.The results show that the horizontal inconsistency of the vertices on both sides of the valley is more significant than the vertical direction.When high frequency waves are incident,the amplitude of the SV wave scattering source on the back wave side increases significantly,and the amplitude of the P wave scattered on the front wave side even exceeds the incident SV wave.;The range,direction of motion and number of vibrations at the midpoint of the slope on both sides of the valley are significantly affected by the slope of the valley,the incident angle and the frequency of the incident wave than the central point at the bottom of the valley;the more comprehensive and sufficient the incident and scattered wave fields of the truncated boundary are,the calculation results are closer to the IBIEM semi-analytical results,considering the scattering effect of the river valley is the essential reason that the total field input method is more accurate than the free field input method.(4)The ground motion characteristics of the valley site under the oblique incidence of the P-SV wave combination are analyzed,and the P-SV wave combination oblique incidence wave input method based on IBIEM is established.The effects of different input methods on the response of an asphalt concrete core earth-rock dam were studied.The results show that the P wave and SV wave have a superposition effect on the contribution of the horizontal displacement component,and have an offset effect on the contribution of the vertical displacement component,resulting in the variation of the two-way peak displacement with the slope of the valley,the incident angle of the P wave or the SV wave,and the frequency.The oblique incidence results are quite different.Compared with the total field input,the acceleration,displacement and stress responses of the asphalt concrete core wall dam under the free field input are significantly different.