Assessment of tunnel induced deformation field through 3-dimensional numerical models (Necatibey subway station, Ankara, Turkey)

Aktürk, Özgür
In heavily settled areas, deformations induced by the tunnel excavation may cause serious damage to nearby structures. In this study it is aimed to model ground deformations induced by main tunnels and connection tunnels excavations as well as groundwater drainage. Therefore, it is necessary to study effective means of controlling tunnel induced deformations. The main parameters affecting the failure and deformation state of the soil around a circular underground opening are the physical characteristics of the soil, the diameter of the opening, and the support pressure. During the construction stage of Necatibey Station of KızılayÇayyolu metro line (Ankara, Turkey), challenging ground conditions involving highly heterogeneous and locally water saturated foundation soils have been encountered. Possibility of damage at the surface and/or on the underground structures can be estimated using finite difference method (FDM) of analysis. In this study, two geophysical methods namely Electrical Resistivity Imaging (ERI) and Ground Penetrating Radar (GPR) were utilized to distinguish soil types at the study area. By correlating these geophysical survey results with the boring v logs, 3-Dimensional soil profile was revealed at the study area to build up a basis for numerical models. 3-Dimensional (3D) FDM analyses were conducted to assess tunneling induced deformations, along with movements around shallow soft ground main tunnels and connection tunnels. During sequential excavations, temporary and permanent shotcrete lining was also simulated. The soil behavior is assumed to be governed by an elastic-perfectly plastic constitutive relation based on the Mohr–Coulomb criterion. The computed deformations around these openings have been compared with the in-situ measurements. The results of the study revealed that the 3-D elasto-plastic analyses yield comparably good correlation with the in-situ measurements. Also, in this study, the effects of main tunnels excavations on each other and the effects of connection tunnels excavations on main tunnels were identified in terms of ground deformations. In order to simulate induced surface settlement due to groundwater withdrawal at the site 3-D fully coupled (fluidmechanical) numerical models were run using different time durations. The model studies revealed that deformations monitored at the ground surface are directly related with the tunnel construction practice. Pumping groundwater has very little or no effect on the measured deformations.
Citation Formats
Ö. Aktürk, “Assessment of tunnel induced deformation field through 3-dimensional numerical models (Necatibey subway station, Ankara, Turkey),” Ph.D. - Doctoral Program, Middle East Technical University, 2010.