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Investigation of factors affecting the performance of roadside noise barriers

University of British Columbia

Roadside noise barriers are used to prevent traffic noise from reaching nearby residences. Two factors that may affect the acoustical performance of highway noise barriers - surface absorption and nearby vegetation - were investigated. Three experimental techniques were used: full-scale laboratory tests, field tests, and scale-model tests. Tests with a 1.2m high barrier on a hard surface were performed in an anechoic chamber, using source and receiver positions corresponding to different diffraction angles. Absorption was added to the wall in various configurations and the change in insertion loss (IL) was measured. IL's of 12-18 dBA behind and -1 dBA in front of the reflective wall were found. Surface absorption increased IL by up to 2 dBA behind the barrier and 1 dBA in front. For the field tests, traffic noise was measured behind reflective noise walls without and with nearby foliage. Effects were small, less than 5 dB, but suggest that vegetation can either attenuate sound, increasing the IL, or scatter sound into the barrier shadow zone, decreasing the IL. A 1:31.5 scale-model highway configuration was created and tested in an anechoic chamber. Scale-model materials were chosen by performing excess attenuation measurements and doing a best fit using flow resistivity. Absorption was tested on single and parallel noise barriers of varying heights, allowing for a comparison between adding absorption and increasing the height. Foliage tests were performed on single and parallel barriers with various configurations of model trees. Barrier absorption prevented the amplification of sound between parallel barriers and adding absorption was equivalent to increasing the height by 0.33 m. The foliage test results were similar to the field tests; the effects were small and dependent on frequency and the size of the foliage. Predicting these results was attempted using ray tracing, the method of images (MOI), and finite element methods (FEM). An existing ray tracing model, PRAY, was modified and used; however the predicted IL’s were 10-30 dB greater than those measured. FEM gave IL's 2-8 dB lower and MOI gave IL's 5-20 dB lower than measurements.

Text

2011-09-21

Attribution-NonCommercial-NoDerivatives 4.0 International

http://hdl.handle.net/2429/37535

Mechanical Engineering

University of British Columbia

UBCV

http://creativecommons.org/licenses/by-nc-nd/4.0/