effects of face excavation patterns on time dependent behavior of tunnel

 a number of numerical analyses were performed to investigate the effect of different patterns of tunnel face excavation, in natm, on the time-dependent behavior of ground due to tunneling. for achieving this aim an elastoplastic-viscoplastic constitutive model implemented in flac code was used. towheed tunnel which was constructed in accordance with the principles of the new austrian tunneling method (natm) as a case study is analyzed by three different face advance techniques. three type of excavation patterns studied in the present work are; twin sidewall excavation (method-a), crown, invert face excavation (method-b), and crown, bench, and invert face excavation (method-c). the obtained results shows that method-a presents a less ground settlement, and can be considered as more proper method for tunnel excavation.