A special support design for a large-span tunnel crossing an active fault (T9 Tunnel, Ankara–Sivas High-Speed Railway Project, Turkey)

Abstract

Throughout construction process of a tunnel in an active tectonic region, it may be impossible to avoid active faults. Active faults create two adverse effects on the tunnels which are sudden fault displacement and weak ground conditions in fault zone. If a tunnel crossed by an active fault, the tunnel might be damaged by sudden movement of the fault. However, the main goal is to localize this damage without complete loss of tunnel. In this study, a special design developed for a wide span tunnel cut by an active fault is presented and the performance of the design is verified by numerical analyses. T9 tunnel was constructed within the scope of Ankara–Sivas High-Speed Train Project, Turkey, and the special design at the intersection of T9 tunnel with the Akdagmadeni active fault is the main subject of this study. T9 tunnel predominantly passes through agglomerate, basalt, marble and gneiss units and the tunnel route crosses the Akdagmadeni fault at around Km: 327 + 915. At this location, major deformations occurred in the tunnel and the tunnel excavation had to stop for a certain period. After the re-design phase, a special tunnel support system for this location were developed and proposed design was analyzed with numerical analyses. In addition, the possible displacement of the Akdagmadeni fault was estimated and the inner lining was re-designed considering the seismic parameters (i.e. peak ground acceleration and maximum displacement during a large earthquake). Consequently, in the present study, the effects of active fault crossing on the tunnel were explained and a special inner lining design was proposed to localize the possible damages, which are originated from the sudden displacement of the active fault.