3D numerical analysis of sprayed concrete lined tunnels: Influence and optimisation of the simulation of varied construction schemes
Summary
3D numerical models require significant effort for their preparation and analysis, translated into time and cost. It is in the hands of the engineer to set the optimal level of simulation detail that will provide a reliable and cost effective solution. In sprayed concrete lined tunnels, a common simplification is to simulate the excavation with full face steps. This assumption can prove effective in minimising the modelling and analysis effort required to check the structural capacity of the concrete lining. However the calculated in-tunnel and surface deformations may not adequately reflect the actual observations due to the behaviour of the calculated lining stresses. The results of such analysis are often utilised in order to establish trigger levels. Therefore, it is imperative that the solution best reflects the real behaviour as much as possible.
The effect of simulating varied excavation sequences of a sprayed concrete lining tunnel on the 3D numerical analysis results, was investigated in this study. The excavation of a 20m long tunnel, 11.2m high and 10.4m wide, enlarged from an existing TBM tunnel (6.4m OD) was simulated using four different excavation sequences: i) full face, ii) top heading, bench and invert and iii) top heading, invert and bench and iv) top heading, combined bench/invert. Moreover, the effect of applying intermediate soil relaxation factors prior to the installation of the lining was also examined. The models were calibrated against real measurements.