Hi all,
In tutorial 7 of plaxis 3D - Phased excavation of a shield tunnel, I wonder why the surface contraction is not applied on the surface of 1.5-m-long ring segments after the TBM because the section 5.5.6 surface contraction in Plaxis 3D reference manual mentioned that "If a contraction was already applied in the previous phase, assigning 0 to the value will implicitly apply a contraction with the same value but in the opposite direction resulting in a zero contraction at the end of the current phase". Therefore, not applying surface contraction on 1.5-m-long ring segments means the volume loss of these segments will return to 0, which is unrealistic. I am modeling tunnel excavation with a volume of 1%, so I wonder whether I should use a surface contract for ring segments after the TBM or just ignore it and follow the tutorial.
Thank you
Hi Nam,
The tutorial for "Phased excavation of a shield tunnel" is now tutorial 5, Please go through the link to view the latest version of PLAXIS 3D Tutorial manual.https://communities.bentley.com/products/geotech-analysis/w/wiki/45388/tutorials-plaxis-3d.
The TBM is modelled as per the conicity, the reduction of diameter for first 7.5m is considered and the last 1.5m to the tail has constant diameter so it has uniform contraction of 0.5% and the remaining sections have linear contraction. So, we have applied the contraction in Phase_1 to model this decrease in diameter between the cutter head and the tail. The tunnel opening has already contracted in shape as per this contraction value (decrease of diameter). Lining is installed after the TBM has passed. Then in Phase_2 we deactivate the plate element(TBM) along with the contraction and activate the volume element that represents the lining, so in the lining contraction is not reverted .So the effect of contraction still exists in the lining from the TBM, however this is a way of modelling in PLAXIS.
Answer Verified By: Kalyani Singh
Thank you Kalyani