بررسی تأثیرات ضخامت، عمق و تعداد لایه‏های ضعیف خاک بر پاسخ لرزه‏ای ساختگاه

نوع مقاله : مقاله پژوهشی

نویسندگان

1 استادیار دانشکده مهندسی عمران، دانشگاه صنعتی سهند، تبریز، ایران.

2 دانشیار دانشکده مهندسی عمران، دانشگاه صنعتی سهند، تبریز، ایران.

3 دانشجوی کارشناسی ارشد، دانشکده مهندسی عمران، دانشگاه صنعتی سهند، تبریز، ایران.

چکیده

شرایط ساختگاه، از جمله شکل و عمق لایه‏ها، نحوه قرارگیری آنها و توپوگرافی منطقه بر پاسخ لرزه‏ای ساختگاه مؤثر است که می­تواند عملکرد زیرساخت‏های حمل و نقل را تحت تأثیر قرار دهد. در این تحقیق، با استفاده از نرم‏افزار DEEPSOIL، تأثیر وجود لایه ضعیف شامل خاک رس نرم و خاک ماسه‏ای سُست بر پاسخ لرزه‏ای ساختگاه با تحلیل غیرخطی در حوزه زمان بررسی می‏شود. رکورد زلزله مورد استفاده در این پژوهش، زمین لرزه 4/7 ریشتری طبس است. اثر پارامترهای مختلف مانند ضخامت لایه ضعیف، موقعیت آن در اعماق مختلف و تعداد لایه‏ها در نظر گرفته شد. نتایج نشان داد که در حالت وجود لایه‌ ضعیف رسی با ضخامت 3 متر و لایه ضعیف ماسه‏ای با ضخامت 5 متر در سطح، شتاب بیشینه به ترتیب 7/2 و 3/2 برابر شتاب در سنگ بستر است. با بیشتر شدن ضخامت لایه ضعیف سطحی، پاسخ لرزه‌ای کمتر بوده و شتاب بیشینه در دوره‏های تناوب بالاتر رخ می‏دهد. مقایسه طیف شتاب برای موقعیت­های مختلف لایه ضعیف نشان داد که وجود لایه ضعیف در نزدیکی سطح زمین و عمق کمتر، بیشترین تأثیر را بر طیف شتاب دارد و موجب افزایش شتاب بیشینه می­گردد. اگر چه تعدد لایه‏های ضعیف موجب کاهش شتاب بیشینه می‏شود، اما طیف شتاب، پیک­های متوالی در دوره‏های تناوب مختلف، به­خصوص برای خاک ماسه‏ای سُست، را نشان می‏دهد.

کلیدواژه‌ها

موضوعات


عنوان مقاله [English]

Investigating the Effects of Thickness, Depth and Number of Weak Soil Layers on Seismic Site Response

نویسندگان [English]

  • Sadegh Ghavami 1
  • Mehrdad Emami Tabrizi 2
  • Elnaz Najafi 3
1 Assistant Professor, Faculty of Civil Engineering, Sahand University of Technology, Tabriz, I. R. Iran.
2 Associate Professor, Faculty of Civil Engineering, Sahand university of Technology, Tabriz, I. R. Iran.
3 M.Sc. Student, Faculty of Civil Engineering, Sahand University of Technology, Tabriz, I. R. Iran.
چکیده [English]

Site conditions, including the shape and depth of the layers, their location, and the area's topography, affect the seismic site response, which can influence the performance of transportation infrastructure. This study investigates the effect of a weak layer, including soft clay and loose sandy soil, on the seismic site response using DEEPSOIL software through nonlinear time-domain analysis. The Tabas earthquake record (Mw=7.4) was selected for site response analysis in this study. Effects of various parameters, such as thickness of the weak layer, its location at different depths, and number of layers were considered. Results showed that in the case of a weak clay layer with a thickness of 3 m and a weak sand layer with a thickness of 5 m at the surface, maximum acceleration increases significantly. As the thickness of the shallow weak layer increases, the seismic response decreases, and maximum acceleration occurs at longer periods. A comparison of acceleration spectra for different weak layer positions showed that presence of a weak layer near the ground surface and at a lower depth has the greatest effect on the acceleration spectrum, increasing the maximum acceleration. Although multiplicity of weak layers reduces the maximum acceleration, the acceleration spectrum exhibits successive peaks at different periods, particularly in loose sandy soils.

کلیدواژه‌ها [English]

  • Seismic Site Response
  • Weak Layer
  • Acceleration Spectra
  • Nonlinear Analysis
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