Abstract: Empirical formula method is one of the most popular-used methods to predict the soft ground deformation induced by tunneling. Various empirical formulae to predict the ground settlement and horizontal movement above shallow tunnels are introduced. Aiming at the asymmetric double-arch tunnel engineering that lies at Jiaozhou Bay in Qingdao, the section ZK2+800.78 which is located in the intersection between main tunnel and ramp tunnel is chosen as a typical cross-section, a three-dimensional model for numerical analysis is established according to geometrical parameters and geological information of the typical cross-section; and dynamic construction process is simulated with finite difference software fast Lagrangian analysis of continua in 3D (FLAC3D). By comparative analysis of the ground settlement and horizontal movement calculated with FLAC3D program and these empirical formulae, the applicability of these methods to predict the ground deformation above asymmetric double-arch tunnel is discussed and evaluated in detail. It concludes that when the strata are in shallow levels, the ground settlement and horizontal movement can be forecast with these empirical formulae approximately. The results also show that the deviation of these empirical formulae increases with the increase of stratum depth. There is a remarkable shortcoming for these empirical formulae that they can only be used to estimate the ground deformation above a single tunnel in a single stratum. FLAC3D has its clear superiority in predicting the ground deformation above asymmetric double-arch tunnel under complicated geological condition.

Key words: asymmetric double-arch tunnel, ground deformation, finite difference method, empirical formula method, settlement trough, horizontal movement trough