Efficiency of vibration mitigation measures (floating slabs) at the latest extensions on lines 2 and 3 of the Athens Metro

Abstract

This paper describes the in situ evaluation of anti vibration mitigation measures introduced in the latest two extensions on lines 2 and 3 of the Athens Metro: (a) extension of line 3 from Aigaleo to Haidari and (b) extension of line 2 from Agios Antonios to Anthoupoli, at the respective crossover (CO) locations 3-02,3-03 and 2-55,2-66 under normal operation conditions. The aim of the ground borne noise and vibration measurement's campaign, after the installation of the proposed anti vibration mitigation measures e.g. floating slabs (FS), was to determine their efficiency to ensure the allowable ground borne noise and vibration levels in all nearby sensitive buildings. For the proposed FST implementation solution the estimated expected noise level at the soil surface were calculated and proven considerably lower from the given criterion. All CO were directly fixed on a FS on continuous mat CDM-DFMA L10 RR50 with lateral bearings by CDM-97. The measurement campaign consisting of measuring the following parameters: the dynamic characteristics of floating slab (natural frequency of the unloaded system), the vibration velocity on the tunnel wall, during normal train operation for 10 train pass byes and simultaneously, and the vibration velocity at the relevant receptors (soil in front of the facade of the closest building), during normal train operation for the above 10 train pass byes. All measurements were carried out during the night, in order to eliminate possible influence of the urban road traffic. Ambient vibrations' level were also recorded and compared to the vibration level generated during Metro vehicles pass byes. The natural frequency of the unloaded by the train on all floating slabs was found to be inferior to 20Hz as per the final noise and vibration study predictions. Moreover the ground borne noise in the nearest - to FS - buildings at all CO locations is significantly lower than the max allowable limits proving the high efficiency of the mitigation measures.