تأثیر میزان تراکم خاک در رفتار لرزه‌ای شمع در نهشته‌های مستعد روانگرایی حین زلزله

نوع مقاله : مقاله کامل پژوهشی

نویسندگان

دانشکده مهندسی عمران، دانشگاه صنعتی نوشیروانی بابل

چکیده

     سازه­ها در مناطق ماسه­ای شل و نیمه­شل اغلب بر روی فونداسیون­های شمعی بنا می­شود. اگر لایه­های ماسه­ای اشباع، باشد، وقوع پدیده روانگرایی بسیار محتمل می­شود. روانگرایی و اثرات آن یکی از اصلی­ترین دلایل خرابی شمع­ها و سازه­های متکی بر آن­ها در زلزله­های اخیر گزارش شده است. یکی از پارامترهای تأثیرگذار در رفتار دینامیکی شمع در مناطق مستعد روانگرایی دانسیته نسبی خاک می­باشد. با افزایش دانسیته نسبی، مدول الاستیسیته، زاویه اصطکاک داخلی، و عدد نفوذ استاندارد خاک افزایش می­یابد. با توجه به روابط موجود در علم مکانیک خاک افزایش دانسیته نسبی موجب افزایش ظرفیت باربری شالوده­ها، بهبود خواص خاک، کاهش نشست نا­مناسب، پایداری شیروانی­ها و کاهش خطر روانگرایی می­شود. می­توان اذعان کرد خاک با دانسیته نسبی بالا از نظر مهندسین خاکی مناسب جهت فعالیت­های ژئوتکنیکی است و شرایط ایده­آلی را حداقل برای طراحی­های استاتیکی فراهم می­کند. در این مقاله با بررسی رفتار شمع­های بتنی و فولادی با قطر­های مختلف در خاک­های ماسه­ای با دانسیته نسبی مختلف تحت پنج زلزله با فرکانس و­ شتاب بیشینه مختلف، اثر دانسیته نسبی بر روی رفتار شمع و خاک و دو مکانیزم مهم خرابی شمع­ها در مناطق مستعد روانگرایی یعنی خمش و کمانش مورد بررسی قرار گرفت. بدین منظور تحلیل تنش- کرنش غیر خطی با استفاده از نرم­افزار تفاضلات محدود FLAC در حالت کرنش مسطح و در نظر گرفتن مدل رفتاری غیر خطی برای روانگرایی خاک انجام گردید. نتایج نشان دادند که افزایش میزان تراکم خاک اگرچه موجب کاهش عمق روانگرایی و متعاقباً کاهش وقوع کمانش شمع می­شود، اما احتمال وقوع گسیختگی خمشی و برشی را افزایش می­دهد.

کلیدواژه‌ها

عنوان مقاله [English]

Effect of Soil Relative Density on the Seismic Behavior of the Pile in Liquefiable Soil

نویسندگان [English]

  • Milad Saeedi
  • Mehdi Dehestani
  • Isa shoosh Pasha
Department of Civil Engineering, Babol NoshirvaniUniversity Of Technology
چکیده [English]

Buildings and bridges on loose to medium dense sands are often built on piles foundation. If sand layer is saturated, liquefaction is likely to occur. In recent earthquakes, liquefaction and its effects have been reported as one of the main reasons for failure of piles and pile-supported structures [1]. When pile foundations are exposed to intense dynamic transverse loads during earthquakes, soil–structure interaction (SSI) plays an important role in allocating the response of pile foundations to lateral excitation [2]. Recent observations after major earthquakes have shown that extensive damages and destructions are still likely to be happened to pile foundations. This problem is significant particularly for pile foundations in loose saturated cohesionless deposits which are vulnerable to liquefaction and lateral spreading during seismic loading. Design procedures that have been developed for evaluating pile behavior under earthquake loading, have many uncertainties to be used for cases involving liquefaction. The performance of piles in liquefied soil layers is much more complex than that of non-liquefying soil layer as a result of the diminishing of stiffness and shear strength of the surrounding soil over time due to the increase of pore water pressure [3].By increasing the density of the soil the probability of liquefaction is reduced liquefaction. Soil compaction increases the soil relative density, modulus of elasticity, the angle of internal friction, and SPT-N of the soil. With regard to the relationships in soil mechanics science increase of relative density causes the bearing capacity of foundation to be increased, improves the soil properties, reduces the inappropriate subsidence, risk of liquefaction, and stabilizes embankments. High relative density is accounted suitable for geotechnical activities and provides the ideal conditions at least for static designs.

کلیدواژه‌ها [English]

  • Soil Relative Density
  • Depth of liquefaction
  • Buckling instability
  • Bending failure

مراجع

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نشریه مهندسی عمران و محیط زیست دانشگاه تبریز
دوره 46.1، شماره 82 - شماره پیاپی 82
بهار 1395
خرداد 1395
صفحه 25-36

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