Abstract
Results of a series of 3D and 2D analyses of open-face tunnelling in marly-clayey deposits are presented in the paper. A parametric study was performed to investigate the influence of initial stress state, soil deformability, shear strength parameters, and soil anisotropy, on settlement prediction. Comparison of 2D and 3D results shows that the settlement trough predicted by 2D analysis agrees well with 3D results when an appropriate amount of unloading prior to lining installation is adopted. It is demonstrated that the load reduction factor significantly depends on shear strength parameters of soil.
Highlights
The main issue of open-face tunnelling (NATM - New Austrian Tunnelling method or open-face shield) in urban environment is the control of surface settlements
Consideration of stress relief and ground movements that occur at tunnel face prior to the installation of lining is essential if reasonable predictions of settlement induced by tunnelling are to be obtained
The 3D process of tunnel construction was simulated in steps over a length of 80m and the steady-state settlement conditions were developed at approximately 30 m (5D) behind the tunnel face
Summary
The main issue of open-face tunnelling (NATM - New Austrian Tunnelling method or open-face shield) in urban environment is the control of surface settlements. Various studies have shown that a crucial role in FE prediction of tunnelling-induced settlement is assumed by the 3D effects of tunnelling, the initial stress state ( the coefficient of lateral earth pressure at rest K0) and the stress-strain behaviour of soil [6,7,8,9,10,11,12,13,14,15,16,17,18,19,20] It has been noted by several authors that the finite element analysis of tunnelling predicts excessively wide transverse settlement troughs, when compared with field data, especially in stiff clays under high K0 conditions (K0 > 1). The FE analysis of settlement above the Dedinje Tunnel, which is part of the Belgrade railway junction, is presented as a case study
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