Sequential Construction Behaviour of Multi-Tunnel Considering an Interactive Approach

In the past few years, india has seen an acceleration in tunnel construction. the number of projects involving more considerable tunnel lengths is rising. There has been substantial growth in projects like pipelines in urban mass transit, railroads, roads and highways, water supply, and sewerage tunnelling activity in india. There are no vertical stack tunnels constructed in india. this study uses an interactive piggyback tunnel model to examine various interaction behaviours when pillar depth varies, or a new construction sequence is employed while maintaining the most-negligible volume loss. This study uses the numerical method for analysis, as no empirical relationship has yet been fully developed. The analysis adopts the greenfield condition, and the TBM approach has been used for tunnelling. The finite element software used for the analysis is PLAXIS 3D with medium meshing. A two-layered multi-tunnel has been modelled by combining the best conditions for both vertical and horizontal tunnels. The studies of different numerical models show that the vertical tunnel ‘upper surpass construction’ sequence with P/D (pillar to depth ratio) equal to one gave an optimal solution. Further analysis of the combined horizontal and vertical twin tunnel illustrates that the ‘upper surpass tunnel’ gave the minuscule settlement when its P/D ratio is 1.