ABSTRACT
This research aims to declare a case study on a twin tunnel constructed by New Austrian Tunneling Method. The twin tunnel is sketched with connected initial linings and separate final linings, due to dimension and obstacles restrictions. Three scenarios of excavation were numerically modeled in order to reduce settlement. The first scenario comprises entire excavation and installation of the initial lining of each section in order. The second scenario simulates the effect of keeping Center Cross Diaphragm during excavation till the entire construction of initial lining. The third scenario evaluates the effect of final lining construction for a section before entire initial stabilization of another. Numerical results show that the third scenario reduces the surface settlement about 44% comparing to the first one, while the second scenario has no significant effect. Furthermore, the ratio of the surface settlement obtained from the third scenario reduces about 40% than the first one.
