Effects of the soil on the noise attenuation of environmental berm barriers

Abstract

Berm mounds are a commonly used technique to reduce the environmental noise levels produced by highways. A berm is a natural noise barrier constructed of soil, stone, rock, or rubble, often landscaped, running along a highway to protect adjacent communities from noise pollution. An earth mound may be constructed using surplus materials at project site, provided there is sufficient land area available for its construction. Therefore, berms are natural environmental barriers, having relative low costs and they are subjectively well perceived by residents. However, exact noise attenuation provided by berms has not been enough explored in the technical literature, as opposed to common barriers made of vertical rigid walls. Although, some highway noise prediction models assign a noise reduction bonus of 3 dB(A) to sound barriers made of earth mounds, experimental assessments have yielded mixed results. Few theoretical reports have studied this particular problem. In this work, numerical analysis using the classical theory of diffraction is performed on a berm made of different types of soil. The model assumes a line source and includes flow resistant data as boundary conditions. By integrating the results, noise attenuation is given in third-octave bands. It is concluded that soil's properties significantly influence the measured results and that this may be one of the causes of varied in-site empirical evidence.