ارزیابی ظرفیت باربری فشاری شمع‌های طویل فولادی کوبشی فراساحلی در منطقه خلیج ‌فارس

نوع مقاله : مقاله پژوهشی

نویسندگان

دانشکده مهندسی عمران، آب و محیط زیست، دانشگاه شهید بهشتی، تهران، ایران

چکیده

استفاده از شمع‌های طویل فولادی کوبشی به ‌عنوان شالوده سکوهای دریایی استخراج نفت و گاز، به ‌دلیل محدودیت‌های فیزیکی، وجود بارهای سنگین و کم بودن ظرفیت باربری لایه‌های سطحی بستر دریا، از پرکاربردترین گزینه‌هاست. روش‌های مختلفی برای تعیین ظرفیت باربری شمع‌ها شامل تحلیل استاتیکی، استفاده از نتایج آزمایش‌های برجا، و آزمون‌های میدانی بارگذاری استاتیکی و دینامیکی شمع وجود دارند. در سال‌های اخیر، استفاده از آزمون‌های برجا نظیر نفوذ مخروط در طراحی شمع‌های فراساحلی، به ‌دلایلی همچون دقت قابل ‏توجه، نتایج پیوسته در عمق، شباهت آن به شمع و مشکلات اخذ نمونه دست ‌نخورده در دریا، گسترش قابل توجهی یافته است. آزمایش‌های دینامیکی نیز به‌ عنوان یک روش جایگزین، اقتصادی و سریع، نسبت به آزمون‌های استاتیکی بارگذاری شمع به‌ ویژه در محیط­های فراساحلی مورد توجه‌اند. در مطالعه حاضر، برای نخستین بار، یک بانک داده جامع شامل پارامترهای مهندسی خاک حاصل از نتایج آزمون‌های آزمایشگاهی و بر جای ژئوتکنیکی همراه با اندازه‌گیری‌های میدانی به‌ دست آمده از آزمون‌های دینامیکی شمع در سه زمان کوتاه، میان و بلند مدت در منطقه خلیج فارس - میدان پارس جنوبی توسعه می‌یابد. سپس، نسبت به انتخاب و کاربرد چهارده روش شامل چهار روش فراساحلی تحلیل استاتیکی و ده روش مستقیم مبتنی بر نتایج آزمایش نفوذ مخروط برای تخمین ظرفیت باربری محوری فشاری شمع‌های لوله‌ای فولادی کوبیده شده در منطقه مذکور اقدام می­شود. نتایج حاصل از روش‌های مختلف با نتایج آزمایش‌های دینامیکی شمع در سه زمان مورد اشاره مقایسه و توسط معیارهای آماری ارزیابی می‌شوند. بر اساس یافته‌های حاصل از تحلیل‌های آماری، کمترین دقت و کیفیت پیش‌بینی برای بانک اطلاعاتی توسعه یافته در روش‌های تحلیل استاتیکی در مقایسه با روش‌های مبتنی بر آزمون نفوذ مخروط ارائه می‌شوند. مقادیر ظرفیت باربری کل به ‌دست آمده از روش‌های تحلیل استاتیکی به ‌طور میانگین 70%، 63% و 35% بیشتر از مقادیر متناظر اندازه‌گیری شده حاصل از آزمون‌های دینامیکی شمع به‌ ترتیب در سه زمان کوتاه، میان و بلند مدت می‌باشند.

کلیدواژه‌ها

موضوعات


عنوان مقاله [English]

Evaluation of Compressive Bearing Capacity of Long Offshore Steel Piles Driven in the Persian Gulf

نویسندگان [English]

  • AmirHossein Shamshirgaran
  • Babak Ebrahimian
Faculty of Civil, Water and Environmental Engineering, Shahid Beheshti University (SBU), Tehran, Iran
چکیده [English]

Long-driven steel piles are widely used in the foundation of fixed offshore oil and gas extraction platforms due to the existence of physical limitations, heavy loads and weak shallow seabed soil layers. There are different methods to determine the pile bearing capacity, including static analysis, using the results of in-situ tests, as well as static and dynamic pile loading tests. In recent years, the in-situ cone penetration test has considerably been developed in the design of offshore piles owing to its high accuracy, continuous recoding across the depth, and similarity to pile. Additionally, the application of in-situ tests for pile design is of great interest due to difficulties in obtaining undisturbed soil samples at sea. The dynamic pile load test is also considered as an alternative and economical way to the static pile load test, particularly in offshore environments. In this paper, for the first time, a comprehensive data bank, including soil engineering parameters derived from laboratory and in-situ tests as well as field measurements obtained from dynamic pile tests in short, medium, and long-term conditions, is developed for the Persian Gulf - South Pars field. Afterward, fourteen methods, including four offshore static analysis methods and ten direct methods based on cone penetration test results, are selected and applied to estimate the axial compressive bearing capacity of steel pipe piles driven in the studied area. The results obtained from different methods are compared with the results of dynamic pile tests at three mentioned times and evaluated using the statistical criteria. According to the findings of the conducted statistical analyses, the lowest precision and prediction quality are provided in the four static analysis methods compared to the CPT-based methods for the developed data bank. The values of pile total ultimate bearing capacity obtained from the static analysis methods are on average 70%, 63%, and 35% higher than the corresponding values measured by the dynamic pile tests in short, medium, and long-term conditions, respectively.

کلیدواژه‌ها [English]

  • Offshore pile
  • Axial compressive bearing capacity
  • Cone penetration test (CPT)
  • Dynamic pile test
  • Persian Gulf
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