3D numerical analysis of sprayed concrete lined tunnels: Influence and optimisation 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. Either two-dimensional (2D) or three-dimensional (3D) analyses may be deployed, with the latter accounting for many of the 3D effects that are not captured in the simplistic, two dimensional approach. In this study, a number of 3D FE analyses were carried out, utilising software—ABAQUS ^[2] . A selection of back-calculated field stresses and concrete stiffness values were modelled using various excavation and support sequences to determine the in-tunnel displacements and lining stresses of the advancing tunnel. Four different excavation sequences were developed and the results were 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 optimal level of simulation for future FE problems. More than 40 different analyses have been performed in order to identify the sensitivity to variations in the inputs in an attempt to replicate the actual in-tunnel monitoring data. Out of those, some were selected as most representative and relevant to the conclusions. The study uses Crossrail Farringdon station as an example, but the conclusions can be considered for similar ground and construction conditions.