بررسی عددی تاثیر ژئوفوم به‌عنوان مصالح خاک‌ریز در تونل‌های کند و پوش بر نیروهای داخلی سازه تونل در حین زلزله

با توجه به کاربرد روزافزون تونل‌های جعبه‌ای شکل در شبکه‌های حمل‌ونقل بین‌شهری و درون‌شهری که اصولاً به‌صورت تونل‌های کند و پوش اجرا می‌شوند، نیاز به بررسی تاثیر مخاطرات طبیعی مانند زلزله بر این سازه‌های ژئوتکنیکی و روش‌های کاهش بار لرزه‌ای این نوع سازه‌ها بیش‌ازپیش احساس می‌شود. امروزه استفاده از مصالح سبک‌وزن مانند ژئوفوم در مهندسی عمران جایگاه ویژه‌ای یافته و بسیاری از چالش‌های علم مهندسی را برطرف کرده است. در پژوهش حاضر، نقش مصالح ژئوفوم به عنوان خاک‌ریز برای تونل‌های کند و پوش بر نیروهای داخلی سازه تونل در حین زلزله مورد بررسی قرار گرفته است. برای این منظور از مطالعات عددی با استفاده از نرم‌افزار اختلاف محدود flac 2d استفاده شده است. پس از بررسی‌های انجام شده مشاهده شد که ژئوفوم به عنوان خاک‌ریز در سطح بالای تونل توانسته به‌خوبی نیروهای داخلی در حالت استاتیکی، لرزه‌ای و کل سازه تونل را تا چندین برابر نسبت به حالت خاک‌ریز خاکی کاهش دهد. این تاثیر برای دیواره و سقف تونل دیده شد. بر اساس نتایج تحقیق حاضر چنین نتیجه شد که خاک‌ریز ژئوفومی جایگزین مناسبی برای خاک‌ریزهای خاکی از منظر بهسازی لرزه‌ای در تونل‌های کند و پوش می‌باشد.

Numerical Investigation of Geofoam Effect on the Internal Forces of Cut and Cover Tunnels during Earthquakes

According to increasing demand of boxshaped tunnels in transportation networks, which are mainly built as cut and cover tunnels, the impact of natural hazards such as earthquakes on these geotechnical structures and seismic load reduction methods of these types of structures is more important than before. Nowadays, the use of lightweight materials such as geofoam plays fundamental role in civil engineering and has solved many of the challenges of civil engineering. In the present study, the role of geofoam materials as embankments for cut and cover tunnels on the internal forces of the tunnel structure during the earthquake have been investigated. The numerical modeling was performed by twodimensional finite difference software, FLAC 2D v7.0. The results of an experimental study were used to verify the numerical model. Time histories of acceleration and bending moments for Kobe and Northridge earthquakes were examined. Based on the analysis, it was observed that the software was able to predict the results of the centrifugal experiment well and provided reliable results. EPS19 has been used as a geofoam embankment in the analyzes. The acceleration time history of the Kobe and Northridge earthquakes with a maximum acceleration of 0.3 g has been used in the analysis. In the numerical model of the present study, the equivalent linear model (ELM) has been used to model the behavior of the geofoam. MohrCoulomb elastoplastic model was used in soil behavior modeling for static analysis. The behavior of the soil in dynamic analyses was considered as nonlinear and modeled with hysteretic damping. The results are determined in the form of bending moment and shear force diagrams for the roof and wall of the tunnel. The diagrams were provided for static and seismic loading conditions. According to the results of numerical studies, it was observed that the geofoam model has a very good performance in reducing the bending moments and shear forces in static and seismic conditions. Present study shows that geofoam, as the cover material of the cut and cover tunnel, is able to reduce internal forces of the tunnel structure in static, seismic loading condition compared to the soil. Based on the results, it was concluded that geofoam is a suitable material for retrofitting the cut and cover tunnels during earthquakes.