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  Problems Encountered in a Large Tunnel Excavated inGraphite Schists

  The T34 tunnel constructed within the scope of Ankara Istanbul High Speed Train Project. During the T34 tunnel excavation, deformations of up to 58 cm occurred between Km: 230+830 - 230+708. These deformations are far above tolerance and caused the failure of tunnel supports. When the deformation measurements were investigated, it was observed that the deformations resulted in the closure of the tunnel section up to about 40 cm. As a result of the deformations in the T34 tunnel, a reprofiling excavation was needed between Km: 230+830-230+708 due to severe deformations and tunnel closure. In in-situ observations, longitudinal cracks occurred in the upper half of the tunnel and this created serious problems on the tunnel stability. In the scope of this study, the reasons of the severe deformations and support system failure in the T34 tunnel excavated in graphitic schists are discussed, and the verification of the support systems successfully applied during the face excavation are demonstrated by numerical analysis. In addition, the proposed excavation and support projects for the face excavation are presented.

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