عنوان مقاله [English]
U7 station as a backup and service center has been situated in the middle of northern-southern Tehran’s metro line 7 project, in which is being excavated using an earth pressure balance (EPB) machine. In this paper, the most appropriate stabilization method for the exterior portal has been introduced, and afterward, the influence of tunnel excavation using TBM upon the stability of the above-mentioned portal has also been investigated in the excavating procedure onset using numerical method. As a result, soil substitution with plastic concrete, which can also be categorized as one of the ground improvement methods, has been selected to mitigate difficulties more effectively. In addition, optimized length of plastic concrete, used to minimize tunnel face displacement and to restrict prospect instability, has numerically been yielded.
In today’s world, development in infrastructure facility systems such as subways is in the public eyes more than ever. These underground openings are situated in urban and/or residential areas covered by soft soils and alluviums. Furthermore, providing a stable span for the TBM operations in a station would be of great importance to avoid encountering any potential hazard like settlement, economic limitation, and even human casualties. Consequently, in EPB mechanized tunneling, fairly proper stabilization method of any station portals is found to be influential.
Methodology and Approaches
In this study, the FLAC3D software has been used to carry out three dimensional (3D) numerical modeling to investigate the influence of plastic concrete on the face stability. In addition, the Mohr-Coulomb criterion has been taken into account for geo-mechanical behavior of soil material surrounding the tunnel. Since EPB machine is not capable of producing fairly enough pressure against the tunnel face to maintain stability at the beginning of the excavation up to 1.5 meters, hence plastic concrete length required for face stability is found to be 1.5 meters. Accordingly, five plastic concretes of 2, 3, 4, 5, and 10 meter long have been inserted to the numerical models. Finally, optimized length and lateral expansion of plastic concrete have generally been designed based on the results obtained from the numerical analysis.
Results and Conclusions
The results of 3D modeling have revealed that required length to fulfill tunnel face stability is 4 meters in respect with face displacement and also ruptured zones. Lateral expansion of plastic concrete, however, should not exceed 1 meter. The results have also demonstrated that plastic concrete plays a significant role in preventing tunnel crown from enormous displacement.