The project considered here is related to the construction of a tunnel for the construction of a new metro line. The tunnel will be excavated at a relatively shallow depth using the conventional method (NATM). From available in-situ geotechnical investigation, excavation will mostly be taking place within green clay (referred to as montmorillonite clay) and marl. The excavation will be done in full section using an advancement length of 1 m.
Figure 1: Tunnel excavation for the new metro line construction
The tunnel is to be excavated in a very dense urban environment, with buildings sensitive to settlements. To reduce the displacements generated in the rock mass after excavation and thus the associated surface settlements, stabilization means composed of an umbrella vault and fiber glass bolting to the front is to be put in place (but not considered in the present PLAXIS analysis though). The support system, at the back of the front, is made up of steel arches and shotcrete. The installation of the steel set is done as close as possible to the excavated front.
As part of the tunnel design process in a dense urban environment context, geotechnical designers must not only properly assess the surface settlement during construction but also provide a safe design of the temporary support in the main section for both shotcrete and steel girders as shown in figure 2.
Figure 2: PLAXIS 2D support capacity diagrams for the tunnel lining
Create the PLAXIS 2D model using the tunnel designer
To run this tutorial case, you will need the following:
To use this Python script:
If you do not have write access to add files to the PLAXIS 2D installation directory, you can use the following alternative approach:
The script is tested with PLAXIS 2D CONNECT Edition V22 Update 1 and Python 3.8.
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