بررسی رفتار بار- جابجایی شمع مارپیچ در ماسه مرطوب و اشباع با استفاده از دستگاه فشار مخروطی همه جانبه

نوع مقاله : علمی - پژوهشی

نویسندگان

1 دانشجوی دکتری، دانشکده مهندسی عمران، معماری و هنر، دانشگاه آزاد اسلامی واحد علوم و تحقیقات، تهران، ایران.

2 استادیار، دانشکده مهندسی عمران، معماری و هنر، دانشگاه آزاد اسلامی واحد علوم و تحقیقات، تهران، ایران.

3 استاد، دانشکده مهندسی عمران و محیط زیست، دانشگاه صنعتی امیرکبیر، تهران، ایران.

چکیده

امروزه با توجه به کاهش یافتن منابع نفت و گاز در خشکی و افزایش روز افزون ساخت و ساز در مناطق ساحلی، استفاده از پی‌های عمیق برای تامین پایداری سکوهای نفتی و تاسیسات در نواحی ساحلی رو به افزایش می‌باشد. شمع مارپیچ یکی از انواع پی‌های عمیق می‌باشد که به واسطه‌ی مزایای خود، مورد توجه بسیاری از پژوهشگران قرار گرفته است. یکی از پرکاربردترین روش‌های ارزیابی عملکرد شمع‌ها، استفاده از مدلسازی فیزیکی می‌باشد که از نظر زمان، هزینه و قابلیت تکرارپذیری نسبت به انجام آزمایش‌های برجا، اولویت دارد. دستگاه فشار مخروطی همه جانبه (FCV) یکی از موثرترین روش‌های مدلسازی فیزیکی انواع شمع‌ها می‌باشد. این دستگاه شکل مخروطی داشته و با اعمال فشار از کف و به واسطه‌ی جداره مخروطی خود، توزیع تنش خطی مشابه با واقعیت در راستای محور دستگاه ایجاد می‌نماید. در نتیجه با اعمال هر فشار از کف، عمق مشخصی از خاک در نمونه‌ی درون دستگاه FCV مدلسازی می‌گردد. در این پژوهش ابتدا دستگاه FCV با ابعادی بهینه و با قابلیت اشباع شدن نمونه طراحی و ساخته شد. این دستگاه تا زمان نگارش این مقاله تنها دستگاهی است که توانایی مدلسازی فیزیکی شمع در شرایط اشباع را دارا می‌باشد. پس از کسب اطمینان از کارایی این دستگاه، رفتار بار-جابجایی شمع مارپیچ تک پره و سه پره در تراکم‌های گوناگون و در شرایط مرطوب و اشباع مورد بررسی قرار گرفت. نتایج نشان داد افزایش تراکم، درگیری خاک و پره را افزایش داده و ظرفیت باربری شمع مارپیچ افزایش می‌یابد. از طرف دیگر با اشباع شدن نمونه ظرفیت باربری شمع کاهش چشمگیری می‌یابد. همچنین افزایش تعداد پره ظرفیت باربری شمع را افزایش می‌دهد.

کلیدواژه‌ها

موضوعات


عنوان مقاله [English]

Investigation of Load-Displacement Behavior of Helical Pile in Wet and Saturated Sand with FCV Apparatus

نویسندگان [English]

  • Ali Jassim 1
  • Navid Ganjian 2
  • Abolfazl Eslami 3
1 PhD Candidate, Department of Civil Engineering, Science and Research Branch, Islamic Azad University, Tehran, Iran.
2 Assistant Professor, Department of Civil Engineering, Science and Research Branch, Islamic Azad University, Tehran, Iran.
3 Professor, Department of Civil and Environment Engineering, Amirkabir University of Technology, Tehran, Iran.
چکیده [English]

Nowadays, given to the scarcity of Oil and Gas resources onshore, and the increasing demand for construction of facilities in coastal areas the use of deep foundations for providing stability for marine infrastructures, such as Oil and Gas Drilling Rigs and Wind turbines, has gained an increasing attraction. Interests in research of helical piles have been arisen due to the advantages of such foundations. Physical modelling is one of the most common method in practice for performance evaluation of deep foundations which provides with the researcher the capability of repeatability. In addition, it is chip and easy-to-execute method compared to the in-situ pile loading tests. Frustum confining vessel (FCV), is one of the most effective tool for physical modeling approach. FCV has a conical shape, which can convert the vertical applied pressure to the base of the vessel, to horizontal stress and to produce a stress distribution similar to the idealized linear stress distribution of soil in situ. Consequently, each base pressure corresponds to a specific embedment depth in real-world. In this study, a new FCV device with an optimized dimensions with the capability of testing model piles in saturated soil samples was constructed. To the best of the author’s knowledge, the newly constructed apparatus is the only FCV with this capability. After performance evaluation of the device, the load-displacement of a helical pile with one and three helices at different relative densities, both in wet and saturated sand, was evaluated. Results indicate that as the relative density increases the interlocking of the sand and helices increases which yields to an increase in the ultimate bearing capacity of pile. On the other hand, the bearing capacity reduces significantly in saturated sands. Also, increasing the number of helices significantly increases the bearing capacity of the helical pile.

کلیدواژه‌ها [English]

  • FCV Apparatus
  • Anzali Sand
  • Physical Modeling
  • Helical Pile
  • Saturated Sand
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