Evaluation of geological model in construction process of sabzkuh tunnel (Case study in iran)

Abstract

Geological and geotechnical surveys, in general, should precede the tunnel excavation to ensure its safety. Also they should be continued during the tunnel excavation, because the geological condition can be changed unexpectedly while the tunnel is under construction. Tunnel face stability is one of the main issues in tunnel excavation in soft and alluvial grounds in order to keep the construction process stable and prevent localized face collapse. Choosing of an appropriate excavation method is influenced by geological and geotechnical studies and comprehensive and appropriate use of these data in tunnel designing. The Sabzkuh tunnel was excavated mainly in fault zones, alluvial, shale and limestones using the conventional and shielded tunnel boring machine (TBM) Methods. An advance length of 1.5 m without any support system caused many difficulties during the excavation of Sabzkuh tunnel. So, to overcome the complicated ground conditions and tunnel collapse, the excavation method were shifted from full face to sequential excavation in addition to decreasing the excavation step. This paper discusses some of the key geotechnical challenges faced in the tunnel design, including characterization of ground conditions, selection of appropriate design parameters, and evaluation of excavation and support installation sequence based on monitoring and analyzing ground behavior during construction.