Evaluation of Soil Constitutive Model Effects on Numerical Modeling of Settlement Induced by Tunneling in Urban Area, Case Study of the Amirkabir Tunnel

Document Type : Research Article

Authors

1 Dept. of Mining, Petroleum & Geophysics, Shahrood University of Technology, Shahrood, Iran

2 Dept. of Mining, Isfahan University of Technology, Isfahan, Iran

3 Western Australian School of Mine (WASM), Curtin University, Australia

4 Dept. of Mining and Metallurgy, Amirkabir University of Technology, Tehran, Iran

10.29252/anm.2019.12567.1411

Abstract

Summary
This paper reflects the role of different constitutive models on the deformations induced by tunneling in the urban area. These constitutive models were applied in finite element analysis of tunnel-induced subsidence for the case study of the Amirkabir Tunnel in Tehran. The results of this paper indicate that the numerical simulation of tunneling induced settlement with hardening soil small strain stiffness model is much more accurate than other constitutive models. 
 
Introduction
Accurate prediction of tunneling induced settlement is one of the most important challenges encountered in urban underground projects. Generally, such predictions are usually obtained by the application of numerical simulation, where the accuracy of the results depends on several factors. The constitutive models play an indicative role in the accuracy of numerical simulation of tunneling induced settlement. This issue was studied by comparing the effect of different constitutive models on the development of ground deformations around the tunnel and the tunneling induced settlement for a case study.     
 
Methodology and Approaches
Finite element analysis of tunneling induced deformations using PLAXIS software was performed for three different elastoplastic constitutive models including Mohr-Coulomb, hardening soil, and small strain hardening. The input data of numerical simulation were captured from different in-suite and laboratory tests on the host ground of the Amirkabir tunnel as a case study. Tunnel construction was modeled based on the as-built condition of the excavation stages of the T4 section of the Amirkabir tunnel. Finally, numerical results were compared and verified with monitoring results and field measurements.
 
Results and Conclusions
Results showed that the Mohr-Coulomb model provides a lower prediction of vertical displacements comparing to two other implemented models. Furthermore, the Mohr-Coulomb model shows an unrealistic uplift of the tunnel floor after all of the excavation stages. Results illustrated that using hardening soil models, with sophisticated features including non-linearity pre-failure and high stiffness under small strain, considerably improves the prediction of displacements. It is observed that using hardening soil small strain stiffness model, the accuracy of predictions increased noticeably compared to the field measurements. A full comparison between the results from Mohr-Coulomb and Hardening Soil cases yields some important differences, which are presented in this paper.

Keywords

Main Subjects


حفر فضاهای زیرزمینی (از قبیل تونل) با جابجایی و تغییرشکل زمین اطراف (محیط درونگیر) و نشست سطح زمین همراه است. بررسی و پیش بینی این تغییرشکل‌ها بویژه برای تونل‌های شهری از اهمیت ویژه‌ای برخوردار بوده و دقت این نوع پیش‌بینی‌ها به شدت به نوع و سطح مدل‌های مورد استفاده وابسته است. با به کارگیری مدل مناسب برای بررسی رفتار جابجایی‌های اطراف فضاهای زیرزمینی مثل تونل، دقت پیش‌بینی‌ها افزایش یافته که این موضوع در نهایت منجر به افزایش کارآیی و کاهش مخاطرات پروژه خواهد شد.

پیش‌بینی جابجایی‌های سطحی (نشست سطح زمین) در فرآیند احداث تونل یک امر بسیار مهم بوده و مطالعات گسترده‌ای در این خصوص انجام شده است. به طور کلی، مطالعات انجام شده در خصوص جابجایی‌ها (به ویژه نشست) ناشی از حفر تونل را می‌توان به روش‌های تجربی[1-4]، تحلیلی[4-9] و عددی[9-13] تقسیم‌بندی نمود. اولین تلاش‌ها برای پیش‌بینی نشست ناشی از حفر تونل با استفاده از روش‌های تجربی انجام شده است. روش‌های تجربی دارای چارچوب محاسباتی ساده‌ای بوده و یک تخمین کلی و ابتدایی از جابجایی‌های ناشی از حفر تونل را ارائه می‌کنند[14،15]. معادلات حاکم بر جابجایی‌های ناشی از حفر تونل در روش‌های تجربی جایگاهی نداشته که در نتیجه، مطالعات جدیدتر به سمت توسعه روش‌های تحلیلی و راه‌حل‌های فرم بسته گرایش پیدا کردند[16،17]. مدل‌های تحلیلی دارای فرضیات ساده کننده بسیار زیادی بوده و در اعمال بسیاری از پارامترهای موثر در اندرکنش تونل و زمین درونگیر شامل پارامترهای ژئومکانیکی زمین، اثر آب زیرزمینی، شکل مقطع تونل و روش حفاری و نصب سیستم نگهداری دارای ضعف شدید هستند. به همین دلیل، در سالیان اخیر، استفاده از روش‌های عددی با قابلیت‌هایی همچون امکان مدلسازی‌ رفتارهای مختلف زمین، امکان در نظر گرفتن رفتار آنیزوتروپ و ناهمگن محیط، قابلیت تحلیل‏ مسائل غیرخطی، قابلیت مدلسازی‌ تونل با اشکال مختلف و امکان اعمال روش اجرایی، استفاده از مدل های عددی برای شبیه‌سازی تغییرشکل‌های اطراف تونل و پیش‌بینی نشست ناشی از حفر تونل به شدت گسترش یافته است[18-21].

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