Effectiveness of added roughness on berm surfaces

The reduction of traffic noise is often achieved using noise barriers or earth berms. More complex solutions have been reported making use of multiple diffraction effects (using complex or combined barriers) or roughened boundaries. Fractal-like surfaces will lead to increased absorption effects. The present paper focuses on the improvement of berms by adding different types of rugosity on its 3 sides. Using a BEM approach, several types of rugosity have been investigated either regular or irregular, simple or multi-level (fractal-like). Global efficiencies have been evaluated considering a realistic four-lane highway combining cars and lorries. In some cases, in a non-refracting atmosphere, a global reduction of 10 dB(A) relative to a smooth berm has been achieved. Effect of surface impedance, berm’s size and a comparison of 2D vs 2.5D computations are also considered.