A field investigation on the vibroacoustic impact of an underground metro line

The paper presents the approach used in a field investigation on the vibration impact of a new underground metro line, focusing on population annoyance. The metro consists of a double barrel tunnel equipped with a slab track system: rails are fastened to elastically supported sleeper blocks embedded in a floating concrete slab, cast on a resilient mat. Vibrations were measured over four weeks inside the metro tunnel (on the rail, floating slab and tunnel ring wall) and inside a selected sample of buildings. Transits were monitored with video recordings. Approximately 30000 vibration recordings were collected. A systematic approach was applied to identify the cases in which the vibrations detected inside the buildings could be attributed to metro transits with a high degree of confidence. This task is critical due to the highly variable soil properties and building structures, and to the presence of diverse vibration sources such as surface transportation and building technical systems. The dispersion of the results due to the different characteristics of the rolling stock was also investigated. The results of the study provided a basis for implementing mitigation measures at the sites in which the vibration levels exceeded the limits prescribed by applicable standards.