Measurement of building foundation and ground-borne vibrations due to surface trains and subways

Buildings located near surface trains and subways are subjected to surface train and subway-induced vibrations. Cutting edge technologies in laboratories and precision manufacturing facilities often include operation of vibration sensitive equipment. Human comfort in the form of feelable vibrations and audible noise in residential and office buildings is also a concern. It is thus imperative to reduce these vibrations inside buildings to acceptable levels with the design of an efficient vibration mitigation system. Incorporation of a vibration mitigation system in a building in design phase requires prior understanding and characterization of subway and surface train-induced base excitations of buildings before and after the construction of a structure to meet serviceability criteria. The vibrations measured at the foundation slab of buildings serve as the base excitation for the building and transmit to the to upper floor levels through columns. The focus of this paper is to quantify the amplitudes and frequency contents of vibration level measured at foundation slab and compare these vibration measurements inside the building at foundation level with the open field measurements. In this context, an exploration of ground-borne vibration characteristics was performed at six sites in the Boston area. Three sites were selected for measuring train-induced vibration and another three were considered for subway-induced vibration study. Vibration measurements were performed on the building foundation slab as well as in open fields adjacent to the building. These vibration measurements were quantified and compared. It was found that in the case of surface train-induced building vibrations, open field vibration levels can be conservatively used in the design of buildings. However due to inconsistency in observations, a similar conclusion was not drawn for the case of subway-induced building vibration. This paper also provides the bases that would allow the designer to estimate the vibration levels in sensitive locations within the building. These estimated levels determine the extent to which mitigation is required to meet vibration criteria.