ABSTRACT
The 2nd stage of West extension works for M2 metro line in Warsaw included the TBM excavation underneath an existing road viaduct which overpassed an operating railway line. Specific modelling works were carried out at executive design stage to verify the ground movements produced by the TBM excavation and hence the impact on such assets. Empirical methods and 2D PLAXIS and 3D MIDAS GTS NX numerical analyses were executed and the acceptable results justified the removal of the soil improvements initially foreseen at feasibility stage. Particular effort was given to correctly model the TBM excavation sequence in order to achieve the target volume loss and 3D modelling allowed to capture viaduct differential movements in longitudinal and transverse direction during tunnelling.
A set of monitoring instrumentation was installed on site including ground pins and levelling pins for manual measurements and mini-prisms and tilt-meters for automatic readings. TBM excavation was completed by November 2020, no damage was induced and monitoring results showed a very good agreement with predicted results. The study of such case history provides a good insight into 2D and 3D modelling of TBM works with particular reference to ground movement and damage assessment.
