A thesis submitted in partial fulfillment of the requirement for the Degree of Master of Engineering, School of Civil Engineering

Thesis (M.Eng.) - Asian Institute of Technology, 1999

Finite element programs SFCUP and CRISP (CRitical State Program) have been used to simulate the SCL-NATM excavation of a tunnel in stiff clay. The excavation process was modelled in two- and three- dimensions conditions with either full-face or staged excavation schemes. The three-dimensional ground behaviour near tunnel face was investigated by finite element program SFCUP and the stiff highly overconsolidated clay was represented with linear elastic soil model. The effects of shotcrete liner and tunnel drainage boundary were investigated by 2-D plane strain analyses with CRISP. Previously published numerical models generally analyzed the ground behaviour in terms of total stress analysis and did not include incremental excavation. Thus those studies have neglected the pore water pressure and transient effects of the tunnel advance. In this study, for the first time, a detailed 3-D modelling of the sequential excavation that closely follows the practical field procedures has been carried out in stress-flow coupled formulation. The results obtained are compared to assess the importance of the arching of soil ahead of the tunnel face, the effects of staged excavation and the effective stress paths of soil elements around the tunnel face.