Routine procedure for the assessment of rail-induced vibration

Railway induced ground-borne vibration is among the most common and widespread sources of perceptible environmental vibration, adversely impacting on human activity and the operation of sensitive equipment. The rising demand for building new railway lines or upgrading existing lines in order to meet increasing traffic flows has furthered the need for adequate vibration assessment tools during scheme planning and design. In recent years many studies of rail and ground dynamics have produced many vibration prediction techniques which have given rise to a variety of procedures for estimating rail-induced vibration on adjacent buildings. Each method shows potential for application at different levels of complexity and at different stages of a scheme. However, for the majority of the procedures significant challenges arise in obtaining the required input data, which can compromise their routine use in Environmental Impact Assessment (EIA). Moreover, as the majority of prediction procedures do not provide levels of uncertainty (i.e. expected spread of data), little is available on their effectiveness. Additionally, some procedures are restricted in that they require specific modelling approaches or proprietary software. Therefore, from an industrial point of view there is a need for a robust and flexible rail-induced vibration EIA procedure that can be routinely used with a degree of confidence. Based on an existing framework for assessing rail-induced vibration offered by the USA department of transportation (FTA) this project investigates, revises and establishes an empirical procedure capable of predicting rail-induced vibration in nearby buildings that can be routinely applied by the sponsoring company. Special attention is given to the degree of variability inherent to rail-induced vibration prediction, bringing forward the degrees of uncertainty, at all levels (i.e. measuring, analysis and scenario characterisation) that may impact on the procedure performance. The research shows a diminishing confidence when predicting rail-induced absolute vibration levels. It was found that ground-to-transducer coupling method, which is a critical step for acquiring data for characterising the ground, can impact on the results by as much as 10 dB. The ground decay rate, when derived through transfer functions, also showed to vary significantly in accordance to the assessment approach. Here it is shown the extent to which track conditions, which are difficult to account for, can affect predictions; variability in vibration levels of up to 10 dB, at some frequency bands, was found to occur simply due to track issues. The thesis offers general curves that represent modern UK buildings; however, a 15 dB variation should be expected. For urban areas, where the ground structure is significantly heterogeneous, the thesis proposes an empirical modelling technique capable of shortening the FTA procedure, whilst maintain the uncertainty levels within limits. Based on the finding and acknowledging the inherent degree of variability mentioned above, this study proposes a resilient empirical vibration analysis model, where its flexibility is established by balancing the significance of each modelling component with the uncertainty levels likely to arise due to randomness in the system

The influence of vibration transducer mounting on the practical measurement of railway vibration

When assessing ground-borne vibration related to railways, careful consideration needs to be given to the mounting and coupling of the transducers. This paper presents the results of research investigating some of these fundamental issues. Different couplant materials and four of the most commonly used transducer-to-ground coupling techniques (spikes, buried, slabs, and the transducer directly plastered to the ground), were compared and analysed within the frequency range 5 Hz to 500 Hz. The data demonstrate that transducer vertical alignment has limited influence at small angles. “Blu-tack” showed to be an adequate couplant. Above 50 Hz coupling systems can influence the reading by up to 20 dB. Using the train as a source of vibration yields a high degree of non-linearity on the coupling systems performance

Issues and limitations on measuring building’s transfer function

In the planning stages for new buildings or transit systems, the effects of railway induced ground-borne vibration need to be considered. The propagation of vibration from the ground to a receiving room is a complex problem. It is common practise, within vibration assessment, for the buildings vibration response to be acquired empirically by ether measuring the response of the building in question via an impact method, measuring the response on an equivalent type of building, or using pre existing published data (from the 70s and 80s) to derive a ground to building transfer functions. This paper compares, as a method of evaluating a building transfer function, impact method with actual rail pass-bys and recently collected response with published generalised response curves. The results presented suggests that, when using the impact method excitation process (point source), the distance of impact location to the building foundation is critical, drastically affecting the resulting transfer function. In addition when using train pass-bys as the excitation process, train length is shown to have an influence on the transfer function assessed. The pre-published data are also shown to have limitations for more recent types of construction

Procedures for estimating environmental impact from railway induced vibration: a review

Railway induced ground-borne vibration is among the most common and widespread sources of perceptible environmental vibration. It can give rise to discomfort and disturbance, adversely impacting on human activity and the operation of sensitive equipment. The rising demand for building new railway lines or upgrading existing lines in order to meet increasing transit flows has furthered the need for adequate vibration assessment tools during the planning and design stages. In recent years many studies in the fields of rail and ground dynamics have encouraged many prediction techniques giving rise to a wide variety of procedures for estimating vibration on buildings. Each method shows potential for application at different levels of complexity and applicability to varying circumstances. From the perspective of railway environmental impact assessment, this paper reviews some relevant prediction techniques, assessing their degree of suitability for practical engineering application by weighting their methodology (i.e. considerations and requirements) against practicality and precision. The review suggests that not all procedures are practicable (e.g. the attainment of representative parameters needed to run the procedures) whilst others predicate on assumptions which revealed to be too relaxed resulting in insufficient accuracy; however, a combination of methods may provide the necessary balance