Accounting for the influence of the free surface on the vibration response of underground railway tunnels: A new iterative method

Abstract

This paper presents a new method for calculating the ground-borne vibration from shallow underground railways. The method is based on an iterative wave-scattering approach, which decouples the problem into two sub-systems: (1) a tunnel embedded in a full-space and (2) a half-space domain for the soil alone. The Pipe-in-Pipe (PiP) model is first used to find the soil response remote from the tunnel, in the absence of a free surface. The reflected wave-field approaching the soil-tunnel interface from the free surface is then computed using a Boundary-Element Method (BEM) model, before applying this as an external load on the tunnel wall to calculate the revised response. The process is repeated for multiple iterations until convergence is achieved. To the authors' knowledge, this is the first time that an iterative approach has been applied to an elastodynamic problem. The results from this iterative PiP-BEM model are compared with those of a coupled Finite-Element-Boundary-Element Method (FEM-BEM) model and found to agree well over the frequency range typically associated with ground-borne vibration. © 2020 Proceedings of ISMA 2020 - International Conference on Noise and Vibration Engineering and USD 2020 - International Conference on Uncertainty in Structural Dynamics. All rights reserved..