Evaluation of the soil layering and soil lens effect on the ground-borne vibrations induced by twin metro tunnels

Abstract

This study aims to examine the effects of surrounding soil layers and furthermore lens properties on induced vibrations by underground railway twin tunnels and comparing with the single tunnel. First, the predicted models for the vibration of the underground tunnel(s) are verified against in situ measurements. The tunnel(s) are assumed to be located in two-layer soil, and the influence of upper soil layer thickness, elastic modulus, and soil layers’ inclination angle (for three values of 5, 10, and 15 degrees) on surface vibrations are investigated. Furthermore, the influence of the presence of soft and stiff soil lens with various thicknesses in several levels respect to the tunnel(s) and the effect of the inclination angle of the soil lens (for two values of 5 and 15 degrees) on the surface vibrations is examined. The results indicate that the layered region around the single and twin tunnels increases the vibrations level up to 10 dB respect to the uniform soil layer. Also, the effect of soil lens with larger thickness is remarkable. The maximum inclination angle of 15 degrees for soil layers and soil lens respectively cause in 9 and 5 dB increase in the surface vibrations level.