عنوان مقاله [English]
The investigation and estimation of surface subsidence and ground settlement is an important aspect in the design of shallow tunnels in urban areas. Proper exploration could lead to correct measures and avoiding any damage to structures over and underground.
In this study, four sections of the east-western part of Tehran’s Metro Line 7 with the most potential for surface subsidence were chosen and studied. This part of the metro project is positioned in the young alluvial deposits of Tehran and consists mainly of fine grained soil. Ground settlement requires three dimensional design. Hence, FLAC 3D was used to investigate the surface subsidence of the ground along the tunnel route in sections mentioned above. One of the most important advantages of three dimensional design is the possibility of stepwise excavation, and to explore the effect of each excavation step on the surrounding ground. Hence, the stepwise excavation was carried out and continued in 1.5 m advancing stages, until the advancement stopped affecting the ground settlement at the point over the tunnel portal considered in the model.
Even though, analytical and empirical methods are unable to evaluate the effect of ground water and the effect of overburden due to the presence of structures and traffic at the surface, because of not installing the monitoring system, analytical methods suggested by Sagaseta, Loganathan and Poulos, Verruijt and Booker, and Bobbet, and also Peck’s empirical method were used to investigate the ground settlement in this project.
After using the various methods to study the four chosen sections of the metro line, and analyzing the settlement curves in these sections, it was concluded that the ground settlements is permissible (except the second section).