The UIC Sustainable Unit working group on vibration has just published the Vibrations State-of-the-Art Report.
In modern daily life, people are exposed to many types of vibration. The vibration is often accepted as obvious and no cause for concern, for example when driving a car or when taking a lift. In some cases, vibration originating from sources outside the house may be felt inside dwellings. This applies for example to heavy road traffic, trams and railway lines, both on surface lines and in tunnels. This vibration is typically observed as a gentle trembling of the house, usually of the floor people are standing on. The vibration itself can generate a rumbling sound, caused by the vibrating building radiating sound into the rooms (known as structure-borne sound). Secondary noise, i.e. rattling of loose doors, pottery, etc., can further amplify the audible noise or make it more noticeable.
Whether or not the vibration can be perceived depends on many factors, including distance to the source, speed and type of the traffic, quality of the road or track, type and build-up of the ground, and the construction of the building itself. Modifications performed in the soil (modification of the sewer network, for example) or even in adjacent buildings can give rise to an increase of vibration or ground-borne noise. Contrary to popular belief, vibration caused by passing trains is far too weak to cause even cosmetic damage (when the structural integrity of the building is affected) to buildings. Nevertheless, residents affected by vibration may experience annoyance and could thus voice concern. The degree to which the vibration sensation is masked by audible noise can also play a role, as well as personal sensitivity.
Railway-induced vibration was first noticed and labelled an issue in relation to underground train lines. It is only in recent times that the vibration from surface lines is getting more attention. Vibration is usually accompanied by ground-borne noise. The relative significance of these two phenomena depends mainly on the soil type. In countries with stiff soils, e.g. solid rock, ground-borne noise is generally more important than vibration, and dominant vibration frequencies are higher (i.e. around 50 Hz). In countries with soft soil such as clay or peat, vibration may be more important than ground-borne noise and dominant vibration frequencies are lower (around 5 Hz). This difference in soil type is an important factor affecting the performance and selection of mitigation measures.
For railways, vibration is most often generated by the contact between the train wheel and the railway track. The vibration then travels from the track, through the ground and into the building foundation. Generally, the strength of ground vibration reduces as one moves away from the track. However, the strength of vibration may increase when moving up floors inside the building due to resonances of the building structure.
There are a number of mitigation measures available that can be applied to either the track or the vehicle. Because local factors (terrain, construction of individual buildings, space etc.) have a strong influence, the effectiveness of these measures can differ greatly from case to case. The prediction of vibration levels is thus a complex process and often involves a large degree of uncertainty. In some cases, especially existing situations, the cost of mitigation may be prohibitively expensive. In assessing vibration and designing mitigation, expert judgement is required.
Guidelines for acceptable levels of vibration vary from country to country. The impact on residents depends strongly on individual and local circumstances. Therefore, any values mentioned in this report should be interpreted with great care.
For new situations (railway lines or residential and other property development), it may be required to assess vibration and propose mitigation measures in the environmental impact assessment. For existing situations, most countries do not have a legal obligation for railway companies to assess and mitigate vibration. However, railways take residents’ concerns seriously and, where appropriate, will support an assessment and consider mitigation measures.
The present report reflects the state of the art, which is mainly based on the experience of the European rail-operating community, publications from academia and consultancy, the results of the collaborative research projects RIVAS and Cargovibes, and the work of standardisation committees, insofar as it has been published.
To consult the dedicated website: https://uic.org/noise