بررسی تاثیر سه‌بعدی تغییرپذیری مکانی مدول یانگ بر اساس تحلیل احتمالاتی نشست سطح زمین در تونل‌زنی natm (مطالعه موردی)

یکی از مهم‌ترین مواردی که در طراحی، تحلیل و ساخت تونل‌های شهری natm موردتوجه قرار می‌گیرد میزان نشست سطح زمین در حین ساخت تونل است. نشست بیش‌ازحد زمین معمولاً به تاسیسات، ساختمان‌های مجاور و زیرساخت‌های شهری آسیب‌های جبران‌ناپذیری وارد می‌کند؛  جهت تحلیل واقعی و بررسی دقیق نشست سطح زمین در حفاری تونل‌های شهری لازم است تا شرایط واقعی خاک موردتوجه قرار گیرد. روش‌های استفاده‌شده مرسوم در ارزیابی نشست سطح زمین معمولاً تغییرپذیری مکانی خصوصیات خاک را در نظر نمی‌گیرند بلکه خصوصیات خاک به‌صورت قطعی در محاسبات لحاظ می‌شود بنابراین در این مطالعه سعی شده جهت مدل‌سازی شرایط واقعی خاک، تغییرپذیری مکانی مدول یانگ خاک با استفاده از یک میدان تصادفی سه‌بعدی مدل شده و با روش عددی تفاضل محدود ترکیب ‌شود سپس با تحلیل‌های پارامتریک از مقیاس‌های مختلف نوسان توسط شبیه‌سازی مونت‌کارلو، برای هر میدان تصادفی ایجادشده حداکثر نشست سطح زمین به دست ‌آید. نتایج نشان می‌دهد که مقدار میانگین و ضریب تغییرات مربوط به حداکثر نشست  به ترتیب با افزایش مقیاس نوسان از 28 میلی‌متر به 31 میلی‎متر و از 0.02 به 0.35 افزایش می‌یابد. همچنین تغییرپذیری خصوصیات خاک هم در بزرگی و هم در توزیع تغییر شکل زمین در سه بعد، موثر بوده و نادیده گرفتن آن منجر به دست‌کم گرفتن خطر نشست بیش‌ازحد سطح زمین می‌شود.

Investigating the 3D effect of spatial variability of Young modulus based on the probabilistic analysis of surface settlement in NATM tunneling (Case study)

SummaryOne of the problems with NATM tunneling in urban areas is the risk of excessive surface settlement during excavation operations. For real analysis and detailed study of surface settlement, it is necessary to pay attention to the real soil conditions. However, the conventional methods are always deterministic, rather than taking the natural spatial variability of soil properties into account. Therefore, in this study, an attempt has been made to model the real soil conditions by spatial variability of the soil young modulus based on a threedimensional random field. By combining finite difference analysis with random field theory, a preliminary investigation has been performed into the surface settlement with spatially random Young modules. For this purpose, a combination of finite difference numerical method, random field, and Monte Carlo simulation is used which is known as the random finite difference method (RFDM). The procedure used is reimplemented by the authors in a MATLAB environment to combine it with The FLAC3D program and a series of parametric analyses were conducted to study the effects of uncertainty due to the variability of soil Young’s modulus on ground movements. IntroductionExcessive surface settlement is one of the major problems we encounter when constructing shallow tunnels in soft grounds. For the analytical study of surface settlement, it is necessary to consider soil properties in design calculations with high accuracy. In this research, the complex RFDM method is used to express the spatial variability of soil properties so that we can show its effects on surface settlement. The results demonstrate that soil variability exerts an influence both on the magnitude and distribution of surface settlement. In addition, it is concluded that negligence of the spatial variability of soil properties in surface settlement probability analysis can lead to underestimation of tunnel design parameters. Methodology and ApproachesTo create a random field, the values of SOF are determined first. Then, a threedimensional random field is created by the random field generation functions. The random field created is assigned to the finite difference mesh by the embedded FISH language in FlAC3D.Finally, 1000 Monte Carlo simulations are performed and 1000 surface settlement curves for each SOF are generated. Results and ConclusionsThe mean values ​​of the Smax in numerical stochastic analysis when the SOF is 60 m is approximately equal to the obtained Smax from the numerical model because with increasing SOF the spatial correlation of the Young modulus parameter increases and is closer to the soil characteristics of the tunnel. In addition, the COV of the Smax tends to be 0.3 with increasing the SOF, but in general, it increases significantly (from 0.01 to 0.3), which causes changes in the magnitude of the Smax (between 5 and 80). Mm) becomes.The spatial variability of the Young modules causes the change in the magnitude of the surface settlement as well as a change in its location, so threedimensional numerical analyzes can accurately display the maximum displacement of the Smax in both a vertical and longitudinal section of the tunnel.