Bedrock effects on ground-borne vibrations induced by single and twin railway tunnels

One of the parameters affecting the underground railway vibration is the existence of a bedrock under a soil layer. The wave that propagates from the tunnel is reflected when arrives on the bedrock and affects the ground surface responses. In this paper, the influence of the bedrock on the responses of the ground surface was investigated for single and twin tunnels through the 2D finite element models. The effect of different elastic modulus of top soil layer and bedrock as well as the influence of various bedrock's depths on the ground-borne vibration were studied, as well. The results show that the soil elastic modulus is more important than the bedrock elastic modulus. When the distance from the tunnel becomes longer, the existence of a bedrock under the tunnel has a significant influence on the ground responses. Determined Insertion Gain for the existence of the bedrock above the tunnel and 30m farther from the tunnel is respectively 2dB and 7dB. The obtained results are identical for both the single and twin tunnels.