Ground settlement caused by perpendicularly crossing twin tunnels, a parametric study: Fid-Bau Portal

Ground settlement caused by perpendicularly crossing twin tunnels, a parametric study

Islam, Md Shariful / Iskander, Magued

Highlights • FEA study examined the interaction between perpendicularly crossing twin tunnels. • The study focused on transverse & longitudinal settlement induced by the tunnels. • Development of settlement at various stages of tunnelling were investigated. • The effect of geometric parameters on the induced soil settlement was explored.

Abstract A series of three-dimensional parametric finite element analyses were carried out to investigate the induced ground surface settlement during the excavation of perpendicularly under and above crossing twin tunnels. Both transverse and longitudinal settlements are investigated and presented in this study. The results suggest that the larger the cover depth, the wider the transverse settlement trough and the more the position of maximum settlement shifted towards the existing tunnel centerline. It is also evident that the lower the cover depth the higher the settlement increase rate is. Other important findings are (i) both transverse and longitudinal tunnel displacements increase with an increase in the pillar distances when the upper tunnel is excavated first and vice-versa, and (ii) the maximum transverse settlement occurs at the centerline of the existing tunnel whereas the maximum longitudinal settlement occurs at and around the excavation face. Furthermore, the effect of various stages of the crossing tunnel excavation and tunnel sizes are also examined, and it is observed that the transverse settlement trough becomes wider and deeper as the new undercrossing tunnel advances away from the existing upper tunnel. It is also found that as the diameter of a tunnel increases, the transverse settlement of both the existing tunnel and the newly excavated crossing tunnel increases regardless of the excavation sequence.