Efficiency of isolated concrete blocks applied in railways slab tracks as mitigation measures for railway-induced ground-borne vibration in tunnels

This paper presents a study of the efficiency of isolated concrete blocks as vibration mitigation measures for railway-induced ground-borne vibration problems in subway metro tunnels. The study is performed numerically, using a 2.5D FEM-BEM model of the tunnel-soil system, a semi-analytical model of the track and a rigid multibody model of the vehicle. This comprehensive model of the train-track-tunnel-soil system is used to simulate the vibration response at the tunnel wall due to train traffic for two different track types: a slab track with isolated concrete blocks and a slab track with direct fastening systems. For the slab track with isolated concrete blocks case, various values for the under-block pad stiffness and block mass are considered in the simulation in order to study the effect of these parameters on the mitigation e ciency of this solution. To quantify this e ciency, the criterion used is the insertion loss of the maximum transient vibration value at the tunnel wall for the slab track with isolated blocks with respect to the slab track with direct fastening systems. The results show two important outcomes: on one hand, the mass of the blocks has no significant influence; on the other hand, quite low stiffness of the under-block pads is required to achieve significant vibration mitigation benefits with respect to direct fastening systems.