ارزيابي رفتار غيرخطي تونل‌هاي دايروي تحت بارگذاري استاتيكي و ديناميكي

EVALUATION OF NONLINEAR BEHAVIOR OF CIRCULAR TUNNELS UNDER STATIC AND DYNAMIC LOADING

رفتار تونل‌هاي دايروي در آبرفت درشت دانه‌ي تهران، با استفاده از مدل هاي رفتاري Mohr-Coulomb و Duncan-Chang تحت بارگذاري استاتيكي و ديناميكي مورد ارزيابي قرار گرفته است. علاوه‌بر بررسي تاثير رفتار غيرخطي و نوع خاك، مطالعه‌ي پارامتري روي متغيرهاي ضريب فشار جانبي خاك و عمق تونل كه تاثير قابل‌توجهي در تغييرشكل ها و نيروها دارند، انجام شده است. نتايج بيان‌گر افزايش تاثير رفتار غيرخطي خاك روي ممان ها و نشست‌ها با كاهش مقدار ضريب فشار جانبي خاك هستند. همچنين رفتار غيرخطي خاك با افزايش عمق و به عبارت ديگر، افزايش تنش همه جانبه، اثر بيشتري داشته است. ضمناً مقادير ممان هاي بيشينه و پس‌ماند ناشي از بارگذاري ديناميكي براي ضريب فشار جانبي كم، با عمق افزايش مي يابد؛ در حالي كه براي ضريب فشار جانبي بالا، افزايش عمق تاثير نامحسوسي دارد.

The effect of different parameters on the static and dynamic behavior of tunnels has been one of the main concerns in previous studies. The effects most investigated are as follows: Soil type and thickness, tunnel depth and shape of tunnel section, coarse grain layers around the tunnel, interaction of twin tunnels and the distance between them, and method of tunnel construction. Generally, the investigations have been followed using physical and numerical methods. Using these methods, the effects of the mentioned parameters on the values of axial forces and lining moments, the relation between depth and settlement variations around the tunnels, the shape of the distribution profile of the surface settlements and etc, have been investigated. In this paper, the behavior of circular tunnels in Tehran coarse grain alluvium has been investigated using Mohr-Coulomb and Duncan-Chang constitutive models under static and dynamic loading. In addition to the evaluation of nonlinear behavior and soil type effects, a parametric study has been performed on the coefficient of the lateral soil pressure and tunnel depth, due to their significant effects on deformations and forces. Numerical modeling has been performed for tunnels with 15, 20 and 25 meter depths and 10 meter diameter. The Loma Prieta earthquake has been used for dynamic loading. Numerical modeling has been performed based on the finite difference method using Flac 2D software. Numerical results show an increase in the effects of nonlinear soil behavior on the moments and settlements with a decrease in the coefficient of lateral soil pressure. Nonlinear soil behavior effects have been increased with an increase in depth or confinement pressure. The maximum and residual moments of dynamic loading have been increased with an increase in depth for low values of lateral pressure coefficient, but, for high values of lateral coefficient, the increase in depth has no significant effect on moments. In contrast, moment variations of static loading show a similar trend for all values of lateral pressure coefficient. In static and dynamic loading, increasing the lateral pressure coefficient will result in more axial forces and less moment values in the tunnel lining.