تعیین فاصله ایمن محل کوبش در عملیات تراکم دینامیکی در مجاورت تونل ها با استفاده از مدلسازی عددی سه بعدی

نوع مقاله: یادداشت فنی

نویسندگان

1 کارشناس ارشد ژئوتکنیک؛ دانشکده‌ی فنی و مهندسی، دانشگاه خوارزمی تهران

2 استاد مهندسی ژئوتکنیک؛ دانشکده‌ی فنی و مهندسی، دانشگاه خوارزمی تهران

چکیده

یکی از بهترین روش های بهسازی عمیق خاک های ماسه ای خشک و اشباع، تراکم دینامیکی است. اجرای عملیات تراکم دینامیکی به علت ارتعاشات زیادی که ایجاد می کند، همواره دارای شرایط ویژه ای جهت ایمنی و پایداری سازه های مجاور یا زیرزمینی است. بدین ترتیب عملیات تراکم دینامیکی باید به نحوی طراحی و اجرا شود که سازه های زیرزمینی مجاور، در اثر ارتعاشات تولید شده پایدار مانده و بهسازی مورد نیاز نیز صورت گیرد. در این مطالعه با مدلسازی عددی سه بعدی بوسیله نرم افزار المان محدود ABAQUS ، حداقل فواصل ایمن در اثر عملیات تراکم دینامیکی برای تونل با قطر ثابت در چهار عمق و سه تراز انرژی کوبش مختلف با استفاده از معیار بیشینه سرعت ذرات (PPV) که توسط آیین نامه های معتبر بیان شده تعیین گردیده است. مطالعات نشان داد ربع اول تونل که در سمت کوبش قرار دارد، ناحیه بحرانی آن است. با افزایش عمق تونل و یا کاهش انرژی کوبش، میزان فاصله‌های ایمن از محور آن کاهش می یابد. همچنین موقعیت نقطه نظیر بیشینه PPV در جداره تونل، در انرژی و فاصله کوبش ثابت، با افزایش عمق، از انتهای ناحیه بحرانی به سمت تاج آن جابجا و برای تونل در عمق و فاصله کوبش ثابت، با کاهش انرژی کوبش، محل وقوع PPV در ناحیه بحرانی ثابت ولی مقدار آن کاهش می‌یابد.

کلیدواژه‌ها

موضوعات


عنوان مقاله [English]

Stability of Tunnels Adjacent to Dynamic Compaction Operation using Three-Dimensional Modeling

نویسندگان [English]

  • Alireza Jahangir 1
  • Amir Hamidi 2
1 Civil Engineering Group, School of Engineering, Kharazmi University
2 Civil Engineering Group, School of Engineering, Kharazmi University
چکیده [English]

Summary
Dynamic Compaction is one of the best methods of deep soil improvement. Dynamic compaction operations generate large vibrations; Therefore it should be designed and implemented in a way that does not damage adjacent underground spaces. In this research, for a tunnel with constant diameter, four different locating depths and three different impact energies are modeled numerically using finite element code ABAQUS. In this way six impact distances from tunnel axis are considered. In order to determine safe distances of dynamic compaction from tunnel axis, peak particle velocity (PPV) values in tunnel which is defined by reliable standards are considered.
 
Introduction
Proposed method consists of repeated dropping of a heavy weight tamper in a predetermined pattern on the weak ground that is going to be compacted. Ground vibrations caused by dynamic compaction can damage adjacent underground spaces such as tunnels and buried structures. At First, by numerical modeling of dynamic compaction, critical zone of the tunnel was determined then variations of maximum PPV location for different depths of tunnel and different impact energies were indicated. Finally safe impact distances from tunnel axis for different depths of tunnel with different impact energies in critical zone were determined by allowable PPV that defined by reliable German, British and Swiss standards.
 
Methodology and Approaches
Dynamic compaction has been modeled by many researches with different numerical methods such as finite element. In this research, ABAQUS finite element code in three dimensional space was applied in three steps. In the first step, gravity analysis was performed to exert initial stresses. In the second step, excavation of the tunnel and installation of lining were performed. And in third step, Dynamic implicit analysis for drop of tamper on soil in ten number of blows with time duration 60s for each impact were considered.
 
Results and Conclusions
This research shows that the critical zone of tunnel is located at the first quarter of tunnel in side of dynamic compaction. Increase in depth of the tunnel, safe impact distances from tunnel axis were reduced. By considering constant impact energy and impact distance by, maximum PPV location at the end of critical zone will move up by increase in depth of the tunnel. Also, assuming constant depth of the tunnel and impact distance, maximum PPV point location was fixed with decrease in impact energy.

کلیدواژه‌ها [English]

  • Dynamic compaction
  • Numerical Modeling
  • Safe distance
  • Tunnel
  • Peak particle velocity
  • ABAQUS
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