بررسي تاثير مشخصات سازه‌هاي سطحي و لايه‌بندي زمين در بارهاي وارد بر پوشش تونل با استفاده از روش المان محدود

Influence of Surface Buildings and Ground Stratification on Lining Loads, Applying the Numerical Finite Element Method

در تونل‌سازي مكانيزه براي نگهداري تونل از پوشش‌هاي بتني پيش‌ساخته استفاده مي‌شود، كه با طراحي اقتصادي‌تر آنها مي‌توان هزينه‌ي پروژه‌ها را كاهش داد. جهت ارزيابي دقيق‌تر بارهاي وارد بر پوشش تونل‌هاي با قطر بزرگ، تاثير پارامترهاي مختلف سازه‌هاي سطحي و مشخصات هندسي تونل به همراه لايه‌بندي زمين و مشخصات خاك پيرامون تونل با مدل‌سازي سه بعدي با استفاده از نرم‌افزار ABAQUS بررسي شده است. براساس نتايج حاصل، لايه‌بندي زمين و وجود سازه‌ها در ميزان بارهاي وارد بر پوشش تونل‌ها موثر است و در مطالعه‌ي موردي سازه‌هاي 5 طبقه و بيشتر، تاثير قابل ملاحظه‌يي دارد. اين آثار براي تونل‌هاي كم‌عمق بيشتر است و اثرات سازه‌ها با افزايش عمق تونل كاهش مي‌يابد. همچنين پارامتر عرض ساختمان، موثرترين پارامتر در مسيله‌ي اندركنش ساختمان و تونل است و با افزايش عرض اثرگذاري، ساير پارامترها نيز افزايش مي‌يابند.

Urban development and increasing population growth have been accompanied by a considerable growth in mechanized shield tunneling. Commonly, precast concrete segments are used as a tunnel lining, which constitutes the largest portion of tunneling costs. The optimum design of lining that decreases tunneling costs requires an accurate evaluation of loads acting on the lining. In this paper, the effects of ground stratification and geometry, position and weight of the buildings on lining loads are studied. For this purpose, a 3D finite element model is used employing ABAQUS software (Ver. 6.10). The main construction aspects and all main elements of the mechanized excavation are modeled: TBM shield, concrete tunnel lining, support of excavation face, over-excavation, tail gap grouting and progressive hardening of the cement based grout. The geometry of the tunnel, lining segments, the injection grout and surrounding soil properties are adapted from the (under construction) Tabriz urban railway, line 2, project. The results show that ground stratification and building properties have a considerable effect on lining loads, and this effect should be taken into consideration in the design. Based on obtained results for the mentioned case study, surface buildings with 5 and more storeys have a considerable effect on lining loads, especially for shallow tunnels. Also, the geometry of surface buildings influences the internal forces of the lining; increasing both building width and length increases the lining loads. The building width is the most important parameter of the tunnel and surface building interaction; by increasing this parameter, the influence of other parameters increases. Also, by comparison of obtained results in this study with results of 2D analysis, the reliability of 2D models, in order to evaluate lining loads, is investigated. The comparisons show that 3D analysis is superior to 2D analysis, particularly in the presence of surface buildings. The difference between results increases with a decrease in building length and an increase in tunnel depth and building weight.