PLAXIS 3D Tutorial 06: Phased excavation of a shield tunnel

04 October 2018

The lining of a shield tunnel is often constructed using prefabricated concrete ring segments, which are bolted together within the tunnel boring machine to form the tunnel lining. During the erection of the tunnel lining the tunnel boring machine (TBM) remains stationary. Once a tunnel lining ring has been fully erected, excavation is resumed, until enough soil has been excavated to erect the next lining ring. As a result, the construction
process can be divided in construction stages with a length of a tunnel ring, often about 1.5 m long. In each of these stages the same steps are repeated over and over again.

In order to model this, a geometry consisting of slices each 1.5 m long can be used. The calculation consists of a number of Plastic phases, each of which models the same parts of the excavation process: the support pressure at the tunnel face needed to prevent active failure at the face, the conical shape of the TBM shield, the excavation of the soil and pore water within the TBM, the installation of the tunnel lining and the grouting of the gap between the soil and the newly installed lining. In each phase the input for the calculation phase is identical, except for its location, which will be shifted by 1.5 m each phase.

The attached *.p3dlog file contains all the commands to generate the models up to calculation (without point for curves selection). With a PLAXIS VIP licence you can use the commands runner to open the *.p3dlog file and to execute all commands in one go. Without a VIP licence, you can open the *.p3dlog file with any text editor, like Notepad, and then execute the commands via the command line command by command.

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