بررسي اثر موقعيت و ابعاد دال‌هاي محافظ تونل بر كاهش آثار ناشي از انفجار در سطح زمين

Effect of Position and Dimensions of Tunnel Guard Slabs on the Reduction of Ground-Level Explosion Loads

مطالعه رفتار و ايمن‌سازي تونل‌هاي مدفون كه شريان‌هاي حياتي هر كشور هستند به دليل اجراي اين سازه‌ها در محيط پيچيده خاك، همواره با دشواري‌هاي زيادي همراه بوده است. از طرفي در سال‌هاي اخير به دليل افزايش تهديدات امنيتي و تروريستي، نياز به بررسي رفتار اين سازه‌ها در مقابل بارهاي انفجاري بيشتر از گذشته احساس شده است. در تحقيق حاضر به بررسي پديده انفجار در سطح زمين و اثر موج ناشي از آن روي تونل‌ مدفون پرداخته ‌شده است و با استفاده از تحليل ديناميكي غيرخطي در نرم‌افزارANSYS-AUTODYN، ابتدا پديده گسترش موج انفجار در خاك در يك محيط سه‌بعدي و با هندسه كامل شبيه‌سازي‌شده و پس از اطمينان از صحت نتايج، اثر عمق دفن دال‌هاي محافظ معمولي و سپس دال‌هاي مركب تقويت‌شده با لايه‌اي از ورق فولادي در زير آن بررسي شده است. در ادامه نيز اثر ابعاد هندسه دال در كاهش آثار مخرب انفجار بر روي تونل، ارزيابي‌ شده است. نتايج حاصل نشان مي‌دهد كه هرچقدر دال محافظ به سازه تونل نزديك‌تر باشد محافظت بهتري از تونل صورت خواهد گرفت. بعلاوه افزايش ضخامت دال بتني همواره باعث كاهش آثار ناشي از انفجار بر روي مقطع تونل مي‌شود اما تغيير طول دال بتني صرفاً نمي‌تواند معيار مناسبي براي پيش‌بيني آثار بار انفجاري بر مقطع تونل باشد.

Summary Study on buried tunnels that are vital arteries in each country, has always been faced with many difficulties due to the implementation of these structures in the complex soil environment. On the other hand, due to increasing security threats in recent years, evaluating the behavior of these structures against blast loads has been felt more than ever. Therefore, in this study, effects of surface explosion on a buried tunnel has been investigated using nonlinear dynamic analysis in ANSYS-AUTODYN software. The effect of the blast wave propagation in soil is simulated with a full geometry in a Three-dimensional (3D) environment and after ensuring the accuracy of the results, the effects of the burial depth of tunnel protective slab and its dimensions in reducing the destructive effects of the explosion is evaluated in a Two-dimensional (2D) environment. The results indicate that better protection of the tunnel will be achieved if the slab is closer to the tunnel structure. Increasing the thickness of the slab always reduces the effects of the explosion on the tunnel but the change in the length of slabs cannot be a good indicator for prediction of the blast loads effects on the buried tunnel. Introduction As enemy weapons are in progress in kind and power, our purpose in this research is to find some methods for making tunnels more safe facing blast loads. Security slabs are the tools that we use to guard the structures of tunnels facing blast loads. Here, we study physics of this security slabs as well as their geometries and distances from the tunnels. Evaluation of other effective parameters of a slab such as the kind of materials and its cross-section seems to be acceptable for future studies of guard slabs of tunnels. Methodology and Approaches In this study, we simulate a complete condition of a surface blast, tunnel and its security slab, soil and air environment. An Eulerian algorithm and dynamic nonlinear analysis are used in the ANSYS-AUTODYN software to simulate the effects of blast loads on tunnel section. In this study, a 3D model is used for blast load propagation in soil while a 2D model is used when we have axial symmetry. Results and Conclusions The results of this study show that pressures and effective strain on tunnels will increase by increasing the distances of slabs from tunnel structures, and when a security slab is placed closer to a tunnel liner, it will be more effective than when it is closer to the ground surface. The results also indicate that increscent of the length of the slab is not necessary to be more than a specified length. In addition, increscent of the thickness of the slab is always effective in reduction of destructive blast loads on the tunnel sections.