Field measurements of sound propagating from a point source over a runway and a grass covered ground have been performed to examine the interaction effect of ground and wind on outdoor noise propagation. In the measurements, two loud speakers were used as sound sources radiating intermitted broad band noise and five receiving points were set in a straight line over a length of 300 m from each sound source. To compare the characteristic of sound propagation on the hard ground with that on the soft ground, the measurements on both grounds were made alternately. As a result, it was confirmed experimentally that the effect of wind on sound propagation depends on the acoustical property of the ground surface. As compared with the sound pressure levels under no-wind conditions, the increase in those under downwind conditions is large in the case of the soft ground, while the decrease under upwind conditions is large in the case of the hard ground. Moreover, the effectiveness of calculating the sound pressure level using the acoustic impedance obtained in the in-situ measurement was clarified.
We have developed a new soundproof system which can reduce wind load in a strong wind. This system will be installed additionally on the existing wall of the viaduct to make it much higher without reinforcing the viaduct and improve the performance of decreasing the outside noise around the railway track. It is composed of metal frames and polycarbonate plates 8 mm thick as a noise insulation panel. In a strong wind, the panel opens for reducing the wind load transmitting to the viaduct, while it is closed in an ordinary state and works as soundproofing. In this study, the performances of noise insulation and vibration were measured when the panel was closed and the mechanical structure was verified in a wind tunnel test. As a result, we confirmed the sufficiency of the noise insulation performance and the efficiency of the mechanical structure for limiting wind load transmitting to the viaduct.