Stability Analysis of Rectangular Shaft for TBM Portal Using Numerical Modeling

In some cases, a vertical shaft with a high cross-sectional area and a suitable depth as a portal for the assembly of a TBM drilling rig, the transfer of staff and equipment is required. If the shaft is used for this purpose, the cross -section of the shaft will be rectangular; otherwise, the cross-section of the circular shaft can also be used. In Iran, more than rectangular cross-section shafts have been used as TBM portals. The main objective of this research is to investigate the stability of rectangular shaft for TBM machine by using the finite difference method FLAC3D software. The results of numerical models show that the value of displacement in the horizontal direction increases with the distance from the corner of the rectangular shaft in depth. Also, the stress concentration in the rectangular shaft corners is very high in comparison to the side walls and will eventually become unstable. In addition, in a rectangular shaft, the amount of bending moment is applied to the support system and causes it to be unstable, which requires the elements of the instrument to reduce the moment. According to numerical modeling results, the rectangular shaft is close to the instability threshold.