Excessive vibrations induced by trains and amplified or propagated through the ground can affect sensitive areas such as hospitals, residences, or telecommunication buildings. However, it has been found that the control of these vibrations can be improved by including materials with a high level of damping between the adjacent ground and the tunnel structure. In this study, the behavior of a new type of mortar called C-COM has been characterized through finite element simulations, and its effectiveness on mitigating vibrations in a tunnel is determined. Five parameters have been proposed to compare the response obtained with the new mortar and the one corresponding to a model with conventional materials. It was found that, using the C-COM mortar, vibration levels can be reduced by 10–20%.