Analysis Of The Seismic Motion Dynamic Stress Path Of A Sedimentary Valley Subjected To Obliquely Incident SV Waves

Hydropower bears immense strategic significance in China’s electricity development.The country’s abundant water resources are chiefly distributed in the western region,where high dams and other cross-river valley projects face various challenges,including severe earthquakes,intricate valley terrain,and thick covering layers.Investigating the distribution law of seismic waves in the deep covering layers of the valley holds great engineering importance as it enhances the seismic stability assessment accuracy of the engineering and liquefaction analysis of the site.This paper focuses on the isosceles trapezoidal sedimentary valley site of an engineering project.Using the finite element software ABAQUS and the input method of infinite element artificial boundary combined with equivalent load,the study numerically analyzes the distribution form of acceleration amplification coefficient and dynamic stress path shape of SV wave oblique incidence on the sedimentary valley site.The study’s main conclusions are as follows:(1)The refraction wave of valley topography has an impact on the acceleration amplification coefficient.When the seismic wave is vertically incident,the positions of the maximum values of acceleration amplification coefficient of the valley with small slope are located in the middle and both sides of the sedimentary layer surface.The positions of the maximum values of acceleration amplification coefficient gradually shift from the surface to the deep soil with an increase in slope.This shift indicates the possibility of liquefaction or softening of the soil inside the sedimentary layer increases sharply.(2)The topographic effect mainly affects both sides of the valley,whereas the central part is affected by the topographic effect of the valley on both sides and the amplification effect of the soil layer.As the valley’s width increases,the amplification coefficient of seismic acceleration in the middle weakens due to the topographic effect,and the one-dimensional seismic motion amplification is shown.As the valley’s width decreases,the topographic effect of the valley on the seismic motion in the middle increases,and the one-dimensional analysis method underestimates the seismic motion amplification effect,thus overestimating the site’s stability.(3)Compared with the vertical incidence,the seismic motion of sedimentary layer is focused and amplified on the oncoming side and filtered and reduced on the back side when the seismic wave is obliquely incident.With the increase of the incident angle,this phenomenon tends to be significant,and the position of the maximum acceleration amplification coefficient moves from the middle of the valley to the oncoming side.(4)When the seismic wave is vertically incident,the dynamic stress paths at the centerline of the sedimentary layer in the valley present vertical reciprocating straightline stress paths,which conform to the law of the horizontal field.However,the dynamic stress paths on both sides of the sedimentary layer in the valley are oblique elliptical stress paths,which are quite different from the law of the horizontal field.When the seismic wave is obliquely incident,the dynamic stress paths at the centerline of the sedimentary layer in the valley present a flatter oblique elliptical stress path,while the dynamic stress paths on both sides of the sedimentary layer in the valley present inclined straight-line and oblique elliptical stress paths.With the increase of the incidence angle,the long axis of the dynamic stress path on the oncoming side of the sedimentary layer in the valley shows an overall increasing trend.