عنوان مقاله [English]
Development of subway systems is considered as an essential need in urban areas. Each line of a subway contains tunnels, stations and mid tunnel ventilation shafts. Concrete Arc Pre-Supporting (CAPS) system and Sequential Excavation, are known as standard methods for the construction of underground stations. When the process is underway, it is necessary to protect surface and underground structures from Subsidence hazards. In this paper, stability analysis and settlement evaluation of Haft-e-Tir Station of Tehran metro line No. 6 have been considered. Geotechnical investigations have shown that the main subsurface layer has been formed of a very dense soil.
CAPS is an executive construction method. In addition to tunnel stability, reduction of surface displacement can be made by CAPS. Numerical simulation has been deemed as a special procedure for evaluation and analysis of settlements. The optimal spacing for concrete arch is an important parameter for the success of the method that is usually determined by 3D modeling. However, 2D modeling methods can be faster to reach an optimal result.
Methodology and Approaches
The optimal spacing for concrete arch of Haft-e-Tir Station has been determined using Sakurai's critical strain approach and allowable by-law stresses. The surface subsidence has beenestimated by two methods namely analytical-empirical and numerical modeling methods. The numerical finite difference method (used in FLAC2D software) has been applied in this research. Analytical Bobet relations have also been used for calculating maximum subsidence. Maximum slope of subsidence curve has been calculated by Peck empirical relations. Kramer criterion has also been used to control the maximum slope of the subsidence curve in both methods.
Results and Conclusions
It is demonstrated that the optimal spacing of concrete arch for Rectifier tunnel, South tunnel, and sections I and II of North tunnel in the Haft-e-Tir Station are 3, 2.5, 3, and 3.5 meters, respectively.