Site investigations and convergence measurements for a twin metro tunnel driven in Ankara clay, Turkey

Abstract

Over population and increase in the traffic congestion in urban areas have led to an inevitable rise in the construction of underground structures. Therefore, a project consisting of 9325m twin metro tunnel construction has been planned by the Greater Municipality of Ankara in order to help to ease transportation problems in Ankara, Turkey. This paper presents the geotechnical properties along the tunnel route, and construction of the Middle East Technical University (METU) twin metro tunnel between 2.720 and 4.000 km as a part of Ankara project III. The twin metro tunnel runs mainly through Ankara Clay above this is artificial fill material. Each tunnel has approximately 38 m2 cross-sectional area and is excavated in two stages in accordance with New Austrian Tunnelling Method (NATM). There have been several drilling holes conducted to investigate groundwater levels and engineering properties of the host medium; these will be examined in the paper. In order to monitor the amount of tunnel closure, convergence measurements taken during construction of the tunnel will be presented and discussed.