صابر اکبری

Evaluation of the interaction between a new and the existing underground structures is one of the important problems in urban tunneling. In this work, using FLAC3D, four numerical models of single- and twin-tube tunnels in urban areas are developed, where the horizontal distance between the single- and twin-tube tunnels are varied. The aim is to analyze the effects of the horizontal distances, considering various criteria such as the deformation of linings, the forces and moments exerted on the twin-tube tunnels and their safety factors, the subsidence that occur on the surface and the nearby buildings, the stability of the single-tube tunnel, and the stability of the pillar lying between the single- and twin-tube tunnels. Considering the above-mentioned criteria, the results obtained indicate that the interaction between the single- and twin-tube tunnels is virtually negligible in the distance more than three times the single-tube tunnel diameter. Also the stability of the pillar lying between the tunnels makes the distance to be chosen at least 1.5 times the single-tube tunnel diameter.

Increasing urban development and social needs for transportation systems bring about construction and extension of urban transportation systems. Considering the fact that the important part of costs relates to excavation and maintenance of tunnels, choosing the single or double tube tunnels is one of the most important decisions in urban tunneling. In case of using single tube tunnel, it should be large enough to accommodate a pair of trains and their appurtenances. However, in case of using twin tunnels, considering that each tunnel is meant to be used for one train, the sections of the tunnels can be smaller. The aim of this paper is to use 3D numerical models for line 1 twin tube tunnels and line 2 single tube tunnel of Tabriz metro to study the various aspects of using twin or single tube tunnels in urban areas. Various criteria have been considered such as: stability of the single and twin tube tunnels, subsidence occurred on the surface and nearby buildings, forces and moments exerted on the twin and single tube tunnels and their factors of safety. In this paper finite difference numerical method (FLAC 3D) has been used to model the tunnels of both lines. The results show that when considering the viewpoint of displacements occurring on the walls of tunnels, using a single tube tunnel with big section will be recommended. However, when the viewpoint of subsidence control and forces and moments acting on segmental linings is taken into account, the use of the twin tube tunnels will be advantageous.

Evaluation of the interaction between new and existing underground structures is one of the most important problems in urban tunneling. In this paper, three-dimentional finite difference numerical model of single and twin tunnels in urban areas has been presented. The aim of this research was to evaluate the effects of changing the depth of excavating single tunnel, in constant horizontal distance, on the interaction of single and twin tunnels considering various criteria including forces and moments exerted on twin-tunnels lining and their safety factors, subsidence of ground surface and nearby buildings, excavation stability of single tunnel and stability of pillar lying between single and twin tunnels. The case study is related to single and twin tunnels of Tabriz urban railway, in northwest of Iran. Results indicated that increasing depth of single tunnel causes average safety factor of Sahand tunnel to decrease (6.52 to 6.35) and that of Sabalan to increase (6.78 to 7.02). As the depth of single tunnel increases, excavation stability of single tunnel increases and surface subsidence decreases. The stability of pillar lying between twin and single tunnels increases as the depth of single tunnel increases.

Evaluation of interaction between new and existing underground spaces is one of the important problems in tunneling in urban areas. In some cases it is necessary to excavate tunnels close to each other’s. This، in turn، will lead to important interaction between these tunnels. In this paper، using 3D numerical modeling of line 1 twin tunnels of Tabriz urban railway، excavation stability of these tunnels، using critical strain of Sakurai، have been studied. Also displacement pattern of lining in both twin tunnels (Sahand & Sabalan) have been investigated. In next step، effect of excavation of these tunnels on the subsidence of surface and adjacent buildings، using Cramer criteria and finite difference method (FLAC 3D)، have been studied. For the purpose of study of the interaction effects between these tunnels، forces and moments that act on the segmental lining of each tunnel and their safety factor have been verified. Eventually، stability of pillar that lies between two tunnels، have also been evaluated. The results show that: 1-twin tunnels of Tabriz metro will be stable during excavation. 2-Surface subsidence due to excavation of these tunnels will have no important effect on existing structures. 3-Safety factors varies between 5-10 on the different positions of segmental lining. 4- Pillar that lies between twin tunnels will be stable