JOURNAL OF ROCK MECHANICS

JOURNAL OF ROCK MECHANICS

Numerical Modeling of Surface Subsidence during Excavation Sequences in the New Austrian Tunneling Method

Document Type : Original Article

Authors
Department of Mining Engineering, Amirkabir University of Technology, Tehran, Iran.
Abstract
As the area of ​​metropolitan areas expands and the population increases, the volume of intra-urban traffic is also increasing. The development of underground communication networks such as underpass tunnels and metros is the most suitable option for solving traffic problems in metropolitan areas due to the lack of interference with the movement of citizens. In this regard, the New Austrian Tunneling Method (NATM) is the best option for tunnel excavation in shallow urban areas and over short distances. For the successful implementation of the NATM excavation method in shallow urban environments, it is very important to estimate and control the displacements of the roof, floor, and perimeter of the tunnel and, consequently, the ground subsidence at each stage of excavation. In this study, numerical modeling in the Plexis software environment has been used to estimate the ground subsidence in section T3 of the Amirkabir underpass tunnel in eastern Tehran.  The numerical model includes a hardening soil behavior model (fully elastoplastic) for the soil mass around the tunnel and an elastic behavior model for the shotcrete retaining system (initial tunnel retaining system) and the tunnel middle wall. Based on the results of this research, after the end of the ninth excavation stage, the maximum total displacement was 54 mm, the vertical displacement of the roof was 53 mm, and the tunnel floor swell was 42 mm. The highest displacements were related to the instability of the roof and the uplift of the tunnel floor due to the increase in horizontal stresses at shallow depths. Also, the maximum ground settlement at the end of the ninth excavation stage was estimated to be about 52 mm, and a settlement depression was formed in the range of 2 to 5 meters from the tunnel middle wall at ground level and will gradually reach equilibrium as the abutment advances. Therefore, controlling the displacement of overburdened soil in the final three stages of excavation of the middle gallery of the tunnel will play a major role in controlling ground subsidence.
Keywords

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