تحلیل قابلیت اطمینان روش میخ‌گذاری در پایدارسازی گودهای شهری-مطالعه موردی یک گود در شهر تهران

نوع مقاله : مقاله پژوهشی

نویسندگان

1 دانشکده مهندسی عمران، دانشگاه تربیت دبیر شهید رجایی، تهران، ایران

2 دانشکده مهندسی عمران، دانشگاه علم و صنعت ایران، تهران، ایران

چکیده

امروزه در پایدارسازی گودبرداری خاکی و سنگی به خصوص در محیط‌های شهری به ‌طور گسترده از روش میخ‌گذاری (Nailing) استفاده می‌شود که عدم قطعیت‌ در متغیرهای مختلف خاک، تأثیر به سزایی بر تحلیل پایداری آن‌ها دارد. روش‌های سنتی در ارزیابی و تحلیل پایداری گودبرداری معمولاً بر پایه معیارهای تجربی و مفاهیم ضریب اطمینان و بیشتر بر روش تعادل حدی استوار است که عدم قطعیت‌ها را در نظر نمی‌گیرند. در این تحقیق از تحلیل قابلیت اطمینان جهت بررسی سه حالت خرابی در گودهای پایدار شده توسط میخ‌گذاری استفاده می‌شود که شامل گسیختگی کلی، بیرون کشیدگی (Pull out) میخ (میلگرد مسلح کننده) و گسیختگی میخ (میلگرد مسلح کننده) می‌باشد. متغیرهای تصادفی در این تحقیق شامل چسبندگی خاک و زاویه اصطکاک داخلی، وزن مخصوص خاک، قدرت پیوند دوغاب-خاک و مقاومت گسیختگی میلگرد می‌باشند. در این پژوهش جهت مطالعه موردی از داده‌های یک گود پایدار شده به روش میخ‌گذاری نیز استفاده شده و تحلیل قابلیت اطمینان نیز با استفاده از نرم‌افزارهای معروف MATLAB و همچنین RT انجام شده است. یکی دیگر از اهداف این مطالعه بررسی میزان تأثیر همبستگی متغیرهای مختلف خاک و نوع توزیع متغیرهای تصادفی بر شاخص قابلیت اطمینان بوده و تحلیل حساسیت به منظور تعیین اهمیت متغیرها در شاخص قابلیت اطمینان نیز مورد بررسی قرار گرفته است. نتایج این تحقیق نشان داد همبستگی بین متغیرهای مقاومتی خاک یعنی چسبندگی و زاویه اصطکاک داخلی تاثیر چندانی بر بیرون کشیدگی میلگرد ندارد در صورتی که بر ناپایداری کلی گود و گسیختگی میلگرد تاثیر قابل ملاحظه‌ای دارند که باید در تحلیل‌ها در نظر گرفته شوند. همچنین این مطالعه نشان داد که نوع تابع توزیع نیز بر شاخص قابلیت اطمینان اثرگذار بوده و در تحلیل و طراحی گودبرداری دارای اهمیت می‌باشد.

کلیدواژه‌ها

موضوعات


عنوان مقاله [English]

Reliability analysis of nailing method in the stabilization of urban excavation - A case study of an Excavation in Tehran

نویسندگان [English]

  • Saeed Ghaffarpour Jahromi 1
  • Naser Shabakhty 2
  • Parastoo Tajik 1
1 Faculty of Civil Engineering, Shahid Rajaee Teacher Training University, Tehran, Iran.
2 Faculty of Civil Engineering, Iran University of Science and Technology, Tehran, Iran.
چکیده [English]

Soil nail walls are being used to support vertical excavations below ground level to construct one or two basements. Also, the variability of in-situ soil properties has a significant influence on the stability of the soil nail walls. Conventional methods of slope stability analysis are usually based on limit state analysis and factor of safety criterion. These methods do not take into account the uncertainties. In the present study, global stability, soil-nail pullout failure and nail tensile failure are chosen to study. Cohesion, unit weight and angle of internal friction of soil and ultimate bond strength along the soil nail and yield strength of nail are modeled as random variables. Computations of reliability are performed using MATLAB and RT software. For better understanding, a case of soil nail wall constructed to support a vertical excavation in Tehran is considered for the study and its stability is evaluated for three failure modes. This research aims first to analyze the reliability of nailing walls and validate it using the Monte Carlo simulation method. In addition, the effect of correlation between soil parameters and distribution of random variables on the reliability index was investigated. By sensitivity analysis, the importance of variables in the reliability index was investigated. Then, the reliability index changes were evaluated with respect to the safety factors. Finally, changes in the reliability index were studied by changing the length of nails and the diameter of the nails. According to the assumptions, the correlation between the soil resistance parameters does not have much effect on the pullout mode if the general failure and pulling modes of the nails have a significant effect and should be taken into account in analyzes, as well as the type of distribution of variables affects the reliability index and the choice of distribution type is important.

کلیدواژه‌ها [English]

  • Reliability index
  • Monte Carlo simulation
  • Types of rupture
  • Excavation
  • Uncertainty
  • Correlation
[1] T. Wu, and L. M. Kraft, Safety analysis of slopes, Journal of Soil Mechanics & Foundations Div., 96(2) (1970) 609-632.
[2] D. D. Genske, T. Adachi, and M. Sugito, Reliability analysis of reinforced earth retaining structures subjected to earthquake loading, Soils and foundations, 31(4) (1991) 48-60.
[3] B. S. Chun, K. M. Kim and D. K. Min,  Study on reliability analysis for reinforced earth retaining walls, Third Asian Geotechnical Conference on Geosynthetics, Korea, (2004) 248–254.
[4] T. Chalermyanont and C. H. Benson, Reliability-based design for internal stability of mechanically stabilized earth walls, Journal of Geotechnical and Geoenvironmental Engineering, 130(2) (2004) 163-173.
[5] F. Nadim, H. Einstein and W. Roberds, Probabilistic stability analysis for individual slopes in soil and rock, In Proc. Int. Conf. on Landslide Risk Management, (2005) 63-98.
[6] S. Sayed, G. R Dodagoudar and K. Rajagopal, Reliability analysis of reinforced soil walls under static and seismic forces, Geosynthetics International, 15(4) (2008) 246-257.
[7] G. S. Babu and  V. P. Singh, Reliability analysis of soil nail walls, Georisk, 3(1) (2009) 44-54.
[8] B. M. Basha and G. S. Babu, Optimum design for external seismic stability of geosynthetic reinforced soil walls: reliability based approach,  Journal of geotechnical and geoenvironmental engineering, 136(6) (2010) 797-812.
[9] X. Z. Wu, Probabilistic slope stability analysis by a copula-based sampling method, Computational Geosciences, 17(5) (2013) 739-755.
[10] B. M. Basha and G. S. Babu, Reliability-based load and resistance factor design approach for external seismic stability of reinforced soil walls, Soil Dynamics and Earthquake Engineering, 60 (2014) 8-21.
[11] C. Jingyu, N. Zhihong, Z. Lianheng anf L. Wei, Case Study on the Typical Failure Modes and Reliability of Reinforced-Earth Retaining Wall, Electronic journal of geotechnical engineering, 21(1) (2016) 305-317.
[12] L. Wang, M. Powers and W. Gong, Reliability Analysis of Geosynthetic Reinforced Soil Walls, In Geo-Risk, Geotechnical Risk Assessment and Management. GSP 285 (2017) 91-100.
[13] P. Lin, J. Liu and X. Yuan, Reliability analysis of soil nail walls against external failures in layered ground, Journal of Geotechnical and Geoenvironmental Engineering, 143(1) (2017) 40-56.
[14] J. Yuan and P. Lin, Reliability analysis of soil nail internal limit states using default FHWA load and resistance models,  Marine Georesources & Geotechnology, 37(7) (2019) 783-800.
[15] Y. Hu, P. Lin, C. Guo and G. Mei, Assessment and calibration of two models for estimation of soil nail loads and system reliability analysis of soil nails against internal failures, Acta Geotechnica, 15 (10) (2020) 1-28.
[16] A. Johari, A. Hajivand and S. Binesh, System reliability analysis of soil nail wall using random finite element method, Bulletin of Engineering Geology and the Environment, 79(6) (2020) 2777-98
[17] A. M. Hasofer, An Exact and Invarient First Order Reliability Format, J. Eng. Mech. Div., Proc. ASCE, 100(1) (1974) 111-121.
[18] R. Rackwitz and B. Flessler, Structural reliability under combined random load sequences, Computers & structures, 9(5) (1978) 489-494.
[19] C. Lazarte, H. Robinson, J. E. Gómez, A. Baxter,A. Cadden, and R. Berg, Soil nail walls reference manual, No. FHWA-NHI-14-007 (2015).
[20] F. B. Ferreira, A. Topa Gomes, C. S. Vieira and M. L. Lopes, Reliability analysis of geosynthetic-reinforced steep slopes, Geosynthetics International, 23(4) (2016) 301-315.
[21] P. Lumb, Safety factors and the probability distribution of soil strength, Canadian Geotechnical Journal, 7(3) (1970) 225-242.
[22] G. S. Babu and A. Srivastava, Reliability analysis of allowable pressure on shallow foundation using response surface method, Computers and Geotechnics, 34(3) (2007) 187-194.
[23] S. Javankhoshdel, N. Luo, and R. J. Bathurst, Probabilistic analysis of simple slopes with cohesive soil strength using RLEM and RFEM, Georisk: Assessment and Management of Risk for Engineered Systems and Geohazards, 11(3) (2017) 231-246.
[24] B. K. Low and K. K. Phoon, Practical first-order reliability computations using spreadsheet, Proc. Probabilistics in Geotechnics: Technical and Economic Risk Estimation, (2002) 39-46.
[25] N. Luo, R. J. Bathurst and S. Javankhoshdel, Probabilistic stability analysis of simple reinforced slopes by finite element method, Computers and Geotechnics, 77 (2016) 45-55.