عنوان مقاله [English]
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.