Tunnelling in fault zones -: Bolu Tunnel, Anatolian Motorway, Turkey

The Bolu tunnel as the most crucial part of the Anatolian Motorway between Istanbul and Ankara is located within the North Anatolian Fault Zone. Site investigation led to an engineering geological model which is dominated by a faulted rock mass consisting mainly of a fault gouge matrix and blocks of hard rock varying in size. Unexpected large deformations that occurred during excavation required additional geological investigation, which gave evidence of a low angle fault system considered to be responsible for these excessive deformations. A special NATM design system has been developed to allow for the modified geotechnical model.