Three-Dimensional Numerical Analysis of Ground Surface Settlement Induced by the Excavation of Shield Tunnels

Abstract

When a shield machine pushes forward it causes the internal structure of the ground to change. Such changes take place on the vertical, lateral, and longitudinal dimensions, and is in essence a three dimensional problem. This study used the Taipei Metro system's double shield tunnels as an example and simulated the excavation conditions of single and double shield tunnels. A three-dimensional analysis model was created using a finite element program, PLAXIS 3D Tunnel. The relationship between tunnel contraction percentage in three dimensional analysis, ground loss used by empirical methods, and ground surface settlements caused by shield tunnel construction were investigated. The relationship between ground loss and tunnel contraction percentage could be represented by a linear equation. Moreover, dual-tunnel combinations were attempted as well as a ground surface settlement curve approximation and comparison on a double shield tunnel. Other than discussing the difference between 2D and 3D tunnel behaviors, suggestions were made for the normalization relationships of 2D and 3D single tunnel contraction percentages and maximum ground surface settlements, which can provide a reference for the analysis and design of similar projects in the future.