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Guidelines On Design of Noise Barriers

Guidelines On Design of Noise Barriers

Contents

  1. Introduction
  2. Design considerations
  3. Aesthetic aspects
  4. Maintenance
    4.1 Design Consideration
    4.2 Materials and Detailing
    4.3 Cleaning
    4.4 Other Maintenance Tasks
    4.5 Access
  5. Checklist
  6. Bibliography / References

4.1 Design Consideration

Noise barriers should be designed so that they require minimal maintenance other than cleaning. Concrete or masonry walls require little or no maintenance during the desirable service life of 40 years, but transparent sections need frequent cleaning and might well need replacing during their service life. Careful design can prevent the need for on-site modifications or other damage during construction that might considerably reduce the life of noise barriers. For example, hammering of panels for fitting into place could cause damage and should be prohibited. Therefore, design should be done carefully with due consideration of the practicability in construction. Plastic panels should incorporate resistance to the effects of ultra-violet light. Surfaces and joints should not include dirt or moisture traps or other details liable to cause rust staining. The effects of weathering on colour and of rainwash on accumulated surface grime should also be considered.

It may be necessary to provide access from the protected side for maintenance purposes and where there is a right of way for pedestrians or cyclists. This may render a barrier vulnerable to vandalism and the choice of form and materials should take this factor into account. It may be appropriate for pedestrian and cycle paths to be lit; where painted surfaces are required, polyamide based finishes will enable easier removal of graffiti. Materials for noise barriers should possess good fire retardant properties and comply with the "Particular Specification for Noise Barrier" published by Highways Department, February 2001. Though there is no specific requirement of service life, noise barrier material manufacturer is, however, required to guarantee for at least 10 years on properties such as colour resistance, stone impact resistance, aging and corrosion resistance, light transmission, fire retardant properties etc.

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4.2 Materials and Detailing

In order to minimise the need for maintenance, attention should be paid to the selection of materials used in the construction of noise barriers. The quality of materials used should be appropriate to the location. For example, barriers built in relatively inaccessible locations or in areas likely to be subject to extreme weather conditions will need more durable components than those which can be more easily maintained or are in relatively sheltered positions. Care should be taken over design details in order to eliminate possible moisture traps which would encourage rot or chemical attack. Alloy and metal fittings should be carefully selected to avoid differences in electrochemical potential which would accelerate corrosion. Plants selected for use in conjunction with a noise barrier should generally be of hardy species which require a low level of maintenance.

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4.3 Cleaning

With the passage of time, barrier surfaces may become stained by contaminants such as water-splash from the road surface, airborne grime, bird droppings, honeydew or sap from overhanging trees. Concrete or masonry noise barriers may not need cleaning in certain locations as the surfaces would be washed by rain water and their textured finish may control staining. Flat surfaces, however, will require regular cleaning as contamination will be more apparent and will detract from the appearance of the barrier. High pressure water jets mounted on purpose built tankers, or hand washing with brushes and low pressure water are suitable treatments.

The frequency of cleaning required will depend on the degree of contamination that occurs. Water splash contamination can be reduced by distancing the barrier from the edge of the carriageway, although this will have the drawback of reducing its effectiveness in attenuating the road traffic noise. Effective road surface drainage will also reduce splash effects by preventing puddles from forming. Bird dropping staining can be controlled by the use of design details or chemical repellents that deter birds from perching on the barrier. A very thin wire at a height of about 50mm along the top edge of the barrier will help to prevent birds resting, thus control bird droppings. Trees and other overhanging vegetation may need trimming or cutting back to prevent abrasion and marking of the barrier. Transparent noise barriers will need to be cleaned more frequently than other types because they will show any contamination more readily or surface treatments can be used. Proprietary-made self-cleansing panels could also be considered where its use is justified.

Purpose-made vehicles fitted with water tanks, hoses, brushes and access platforms would reduce the cost of cleaning barriers but long lengths of barrier will be required to justify the necessary investment. In the short term, access platforms can be used to reach the far sides of barriers in order to carry out cleaning and other maintenance. Noise barriers erected near to the carriageway may require lane closures during maintenance; traffic management will be especially important for access to any barriers in the central reserve. Their use is not encouraged, but zero maintenance barriers (self cleaning, impact resistant) would be appropriate in this location.

Similarly, it would be difficult to clean the outside of noise barriers erected on high level structures, as such zero maintenance barriers should be used.

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4.4 Other Maintenance Tasks

In addition to cleaning, other maintenance tasks include :

a) Tightening joints and fixings after initial construction. This should take place at the end of the construction maintenance period.
b) Painting or treatment of metal surfaces. This requirement can be reduced by using anodized aluminium, galvanized or weathering steel. But colours may need to be refreshed periodically if they are an important element in the design.
c) Periodic maintenance of planting - weeding, replacement of failed plants and, if necessary, watering to secure the proper establishment of the vegetation in the initial period, followed by periodic thinning, or pruning as necessary. (Barriers composed of living material retaining earth require a more intensive management regime.)

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4.5 Access

The need for future maintenance should be taken into account when deciding on the form of a noise barrier. Where it will need to be inspected from time to time, screen planting should be placed with sufficient space to permit easy access. Doors or gaps should be provided at reasonable intervals to give access to either side of the barrier. Frequent access will be needed to clean both sides of a transparent noise barrier - on bridges and viaducts this might necessitate the use of specialized equipment. Working area will be required for erecting platform or parking of vehicle with hydraulic lifting platform that can reach both sides of the noise barrier for the carrying out of maintenance works.

Gates or gaps should be provided at about 200m intervals to provide access for the maintenance of both the noise barrier and any planting behind the noise barrier. Where possible these access points should be located to provide access to any traffic control and communications equipment.

Where access point is to be provided for pedestrian but doors are not practical, then, another section of parallel barrier should be provided in front of the access point to avoid degrading of the acoustic performance. One face of this barrier should be provided with absorptive materials to avoid multiple reflections between parallel barriers. The length of this additional barrier should be at least several times of the width of the gap/opening (3x) or as a rough guide, x + 2y, where x is the width of the gap and y is the spacing of the two barriers, whichever is larger. See the figure below for different arrangements at the opening. The exact length required should be worked out during detail design stage having considered standard acoustical principles and practices.

Figure 4.5.1 Arrangement of barriers at opening

Arrangement of barriers at opening Arrangement of barriers at opening

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Friday, 28 April, 2006