Noise protection walls (Design and construction)

Since 1972 between 250,000 and 300,000 m2 of acoustic screening (noise reduction) barriers have been built in France, i.e., 70 - 80 km of such structures of medium height (2 - 6 m), along the roads. They have been installed under a policy of both road and rail traffic noise control which requires the builders of traffic routes to ensure that the sound level at the facades of existing buildings is below 65 dB(A). On the basis of the experience that has been gained, it is now possible to give guidance in respect of design and construction on the following main points: - Acoustic effectiveness: to be effective, the barriers must satisfy certain conditions: they must be sufficiently long and high (dimensional design linked to the diffraction of sound waves), not transmit noise and absorb noise in the relevant frequency range; these criteria govern the shape of the barriers and the materials of which they are to be constructed. - Optimization of the construction of the barriers: using materials suited to the purpose, requiring little maintenance and able to withstand loads (wind). Investigation oi foundations compatible with their location and as economical as possible. - Saiety: for adjacent residents as well as for road users. - Operation and maintenance: particularly taking account of damage due to vandalism, of fire resistance and of cleaning. - Aesthetic appearance of the barriers and their incorporation in an urban environment. To meet theses requirements, many different solutions for noise reduction barriers have been sought and tested in France. Nowadays, about 60 % of the various forms of construction are of concrete. Others use transparent materials (glass and plastics about 20 %), metal (about 10 1.) and clay-based materials (foamed clay, resonator bricks about 10 %). In the years ahead the annual demand for noise barriers is bound to expand further, at a rate of 20,000 to 30,000 m2, on account oi the continued application of this policy on new roads, the execution of a programme to catch up on noise control on old roads and the extension of these protective measures to include secondary roads. The materials used should be further improved in order to enhance their effectiveness and to reduce their cost while continuing to satisfy strict requirements as to aesthetic appearance. The market should aim for: - More effective technological solutions from the acoustic point of view (barriers with a substantially higher sound-absorbing performance than the present ones, resonators, sound-absorbing baffles, etc.); concrete can be the material used wholly or partly in these new solutions, including sound-absorbing barriers • - Quantity-produced basic components, optimized in respect of the material~ used; they must comply with the new codes of practice concerning the forces to be resisted, vandalism, fire hazard and maintenance: a procedure for quality assurance of che materials and aids to innovation will be established in 1986. - Construction of foundations suited to these special structures (walls of great length, but small width). - Taking advantage of possibilities of varying the appearance of these basic components in order to maintain a high level of visual quality in urban surroundings.