Estimation of required thrust for tunnel excavation using 3D numerical modeling- Beheshtabad water transmission tunnel as a Case Study

In this article at first Beheshtabad water transmission tunnel is introduced and mechanized and D&B excavation challenges in squeezing grounds are explored, and the appropriate approaches to reduce the required thrust are presented. then the thrust evaluation methods are considered and the required axial force to penetration in the face according to advance rate, geometry of cutter head and compressive and tension strength of rock is calculated. on the next step, Geomechanical rock mass parameters in 19th chainage are determined, and the numerical method scheme which is applied to thrust determination is discussed and its results are considered. In following, the required thrust to overcome shield skin frictional resistance using Romani''s method is calculated and the obtained results are compared to numerical ones. For application of double shield TBMs in 29030-31600 and 34900-37490 km of tunnel for the most favorable geotechnical parameters three cm and for the least favorable geotechnical parameters ten cm over cutting is essential. In 31600-34900 km utilizing double and single shield TBMs aren''t possible and to decide on the usage of double and single shield TBMs a exploration gallery should be planned and executing additional tests to determination of long term parameters of host rock is required.