مطالعه تشدید تپه‌های متناوب مجاور

توپوگرافی و خصوصیات زمین‌ شناسی تاثیرات معنی‌داری در پاسخ لرزه‌ای زمین دارند. بیشتر مطالعات بر تقویت ناشی از یک توپوگرافی واحد متمرکز شده‌اند. تحقیقات محدودی در مورد توپوگرافی‌های هم‌جوار انجام شده است. در این مقاله، تشدید تپه‌های همگن و غیر همگن با هندسه نیم‌دایره‌ای در حالت متناوب بررسی شده است. جهت مطالعه تشدید تپه‌های متناوب قرار گرفته در کنار یکدیگر از تپه‌ها با فواصل صفر، 0/5، 1 و 2 برابر ارتفاع تپه مبنا شده است. از سوی دیگر به‌منظور بررسی اثرات ارتفاع تپه مجاور بر پاسخ لرزه‌ای تپه مبنا، ارتفاع تپه مجاور 0/5، 1، 1/5، 2 و 3 برابر ارتفاع تپه مبنا در نظر گرفته شد و پاسخ لرزه‌ای مورد مطالعه قرار گرفت. لازم به ذکر است مقایسه‌ها برای حالتی که تپه به‌صورت تنها قرار گرفته باشد مورد مقایسه و تحقیق قرار گرفتند. نتایج به‌دست‌آمده در این تحقیق نشان می‌دهد که افزایش فاصله بین تپه‌های مجاور یکدیگر، تقویت را کاهش می‌دهد. همچنین نتایج حاصل از پژوهش نشان می‌دهند که افزایش ارتفاع تپه کناری تا سه برابر ارتفاع تپه پایه مورد مطالعه، تقویت را تا 40 درصد افزایش می‌دهد. نتایج به‌دست‌آمده از این تحقیق بیانگر این مطلب است که هندسه تپه مجاور بر پاسخ لرزه‌ای تپه پایه تاثیر می‌گذارد.

amplification study of adjacent alternating hills

topography and geological characteristics have significant effect on seismic response of structures. most studies have focused on the amplification caused by a single topography. limited research has been conducted on adjacent topographies. the main aims in this paper are studying the most important factors that affect the amplification ration in the hill topography. the angle between the layers one hill, have a distinct effect of this ratio. in this research, this angle and its effect on the amplification ratio is studied. another important issue is the adjacent hills and their interaction on each other. in the other word, the distance between the adjacent hills, the geometry shape of the hills, homogenous and non-homogenous soil parameters are the most important factors. these factors are studied in this research with a vast numerical analysis based on finite difference method. it should be mentioned that all the models are in dry condition, so the water table level is neglected in the numerical analyses. the effects of these parameters are studied on the amplification ratio of the base hill. the base hill is assumed the hill without any topographic situation near it, for example hill or valley topography near the base hill. in this paper, the amplification of homogenous and non-homogenous hills with semicircular and alternating geometry has been investigated. flac2d software is a finite difference program of itasca software that is used for continuous environments. in order to investigate the effect of the distance between topography, intermittent semicircular hills are located at distances of 0.0, 0.5, 1.0 and 2.0 times the height of the hill. in order to investigate the effect of lateral hill height on the seismic amplification of the studied topography, the height of the side hill is 0.0, 0.0, 1.5, 2.0 and 3.0 times the height of the studied hill. the distance between the hills is half the height of the studied hill. in order to study the geometry of the side hill on the results of the resonance of the studied hill, the side hill is considered in triangular, semicircular and trapezoid geometry. the geometry of the studied hill is semicircular and the height of both hills is equal. due to the semicircular geometry, ratio of height (h) to half the width of the hill (l), equal to (h/l=1). the mesh sizes of the models are taken 2× 2 meters. in software modeling, the model boundaries should be considered so large that the waves reflected from the borders are almost dumped and have no effect on the results. ‏‏ the ratio of maximum displacement of the desired point in the model with topography (pgd response) (peak ground displacement) to the maximum displacement of the desired point in the reference model (pgd reference) is expressed as magnification in displacement (ux). the obtained results in this research show that increasing the distance between the hills, decreases the amplification. the results show that increasing the height of the side hill up to 3 times the height of the studied base hill, increases the amplification up to 40%. the results indicate that geometry of the adjacent hill affects the seismic response of the base hill. reducing the shear wave speed in the non-homogeneous hill reduces the amplification of the base hill compared to the homogenous hill. for adjacent non-homogenous hills, resonance increases, so amplification decreases in the homogeneous base hill. the obtained numerical results show that the adjacent hill’s geometry shape, its distance to the base hill, the non-homogenous soil properties of the adjacent hill and also the layering in the adjacent hill, have distinct effects on the amplification ratio of the base hill.