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  3D numerical analysis of sprayed concrete lining tunnels: influence and optimization of the simulation of varied construction schemes

  In tunnelling, the use of finite element (FE) modelling to determine lining stress and in-tunnel displacement is a commonly employed practice. Two modelling techniques used are two-dimensional (2D) and three-dimensional (3D) analysis, with preference being to the latter. This is to account for many of the 3D occurrences that are not captured in 2D FE modelling despite their computational complexity. In this study, a number of 3D FE analyses utilising analysis software - ABAQUS were simulated. A selection of back-calculated field stresses and concrete stiffness values were modelled using various excavation support sequences to determine the in-tunnel displacements and lining stresses of the advancing tunnel. In order to verify the predicted effect of the advancing tunnel, four different excavation advance sequences were developed for the 3D FE analysis and the results compared with field measurements observed at Crossrail’s Farringdon Station. Using a well-instrumented tunnel as a case study, the paper aims to demonstrate how a very detailed sensitivity study and 3D numerical analysis can be used to determine the choice of excavation sequence for future FE problems. More than 40 different analyses have been performed in order to identify sensitivities to variations in the inputs and to captrue the monitoring data. Out of which only a few are selected as most representative and relevant to the conclusions. The section chosen derives from the authors’ work on Crossrail Farringdon station, but it is considered very representative for similar ground and construction conditions. The results of this work discusse the sensitivities of different approches in the modelled excavation sequence and advance rates, i.e. when the seqquence is altered from full face excavation to a combination of top-heading, bench/invert then the in-tunnel deformations and lining stress values also changed in terms of the face advance pattern adopted. The findings of the sensitivity study with variouss models are compared with field measurements in order to inform an FE modelling campaign optimisation.

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