3.10 Exploration, development and detailed design phase

Once planning approval has been granted or is expected to be granted, the detailed design phase commences. During this phase of the project most of the work that was done during the planning phase will be revisited in more detail. Three critical, interrelated outputs must be achieved and documented in this phase:

  • a detailed plant and equipment noise specification for suppliers
  • a detailed review and design of mitigation measures, including a schedule showing the position and height of noise mounds or engineering designs or performance specifications for special enclosures and cladding of buildings
  • a noise management plan. Developing such a plan is often a condition of project approval, and implementing the plan will fulfil licensing requirements.

3.10.1 Plant and equipment specification

It is critical that the assumptions about noise levels of equipment made during the environmental assessment phase are understood and correctly transferred into specifications for the supply of plant and equipment. These should specify noise levels under certain load or speed conditions at certain distances from each side of the plant. There are Australian and/or international test standards which should be quoted where possible to avoid any ambiguities in the supply of equipment. The specification should also require the equipment to be tested by independent accredited personnel once delivered or installed on site (refer Section 3.10.1).

If buildings or claddings which house equipment are being specified, either a detailed design or a performance specification should be included. Where noise is concerned, attention to detail matters. A rule of thumb is that 90 per cent of the noise can escape from a 10 per cent opening. If the operator has gone to the trouble to design a concrete-clad building with excellent sound transmission loss, but forgotten to treat the openings for fresh air, the effort and expense will have been in vain.

3.10.2 Environmental management plan including noise and vibration

The noise and vibration management plan should be developed during the detailed design phase. Its major purpose is to demonstrate the company’s commitment to achieving environmental goals (usually, the noise criteria in conditions of consent) by clearly establishing the existing environmental noise, stating the design objectives and statutory requirements, and describing the control measures, the emissions monitoring and reporting program, the procedures for handling of any exceedances, and the complaints and community liaison procedures.

It is likely that more ambient noise monitoring will be conducted and the computer model developed for the environmental assessment will be further refined and updated as more certainty about plant types and locations is developed (see Section 3.10). As this occurs, the noise mitigation techniques should be reviewed in detail.

CASE STUDY: The world’s quietest haul truck

Mines in the Hunter Valley of New South Wales have some of the most stringent operational noise compliance criteria in the mining industry. A consultant was engaged to acoustically attenuate three new Caterpillar 789C haul trucks with the purpose of successfully achieving 113 dBA for both static and dynamic tests.

image3-10-2a.jpg

The first treated truck was successfully noise tested achieving 110 dBA for dynamic tests and 106 dBA for the static test, compared with 123 dBA/119dBA for an untreated truck. The noise performance was achieved with no impediment to the truck’s cooling system.

The project began with discussion with the client, identifying the client’s expectations. This was followed by testing an acoustically untreated 789C haul truck to gather baseline noise data. Sound intensity measurements were also undertaken. Sound intensity measures the directionality of a noise source, in addition to the magnitude of sound, which can provide a more accurate assessment of where problematic noise sources are located on a machine.

Baseline measurements, based on ISO 6395 and ISO 4872, enabled the consultant to establish how much a standard CAT 789C needed to be acoustically attenuated in order to meet the specification. However, these measurements did not provide sufficient information for the isolation of problematic noise and specific frequencies.

Detailed noise mapping and analysis of the trucks was undertaken using sound intensity with consideration to ISO 9614–1. The acoustic analysis enabled the consultant to isolate specific problematic noise areas and their dominant frequencies. The acoustic analysis also provided an indication of where the attenuation effort needed to be focused and where a less aggressive attenuation approach could be undertaken.

Critical information gathered through discussion with the client (and operators) provided the engineering team with invaluable information to address key serviceability and functional performance criteria.

image3-10-2b.jpg image3-10-2c.jpg

The design process encompassed:

  • consideration of manufacturing techniques
  • acoustic modelling
  • exploratory manufacture and test manufacture
  • consideration of serviceability, occupational health and safety, standardisation, functional performance (payload and truck cooling) and durability, including exposure to engine liquids, dirt accumulation and fatigue, as well as high-pressure water cannon cleaning
  • design of related items such as access systems (stairs, bumper system, walkways).

3.10.3 Hierarchy of controls

Measures which are commonly adopted under the noise and vibration management plan include (in order of decreasing effectiveness):

  • Selecting lower noise plant and equipment incorporating available noise control kits. This should be one of the first measures chosen to minimise noise impact. For example, exhaust and radiator silencers on large earthmoving plant will generally result in a 5 dBA noise reduction. When investigating engineered solutions for plant and equipment, at the very least consideration should be taken for thermal performance, servicing requirements, occupational health and safety, and weight limit restrictions.
  • Adding attenuators to mine ventilation fans. As with silenced plant items, this should be one of the first management options adopted, to ensure that fan noise levels will be reduced by a predetermined margin and emissions will not exceed acceptable limits.
  • Providing acoustical enclosures and acoustical treatment of process buildings. This is a very effective solution for crushing plant, coal washeries and the like. A reduction in the order of 10 dBA can be expected from a lightweight sheet metal enclosure. Ventilation openings should be oriented away from noise-sensitive receivers.
  • Regulating emissions from reversing alarms. ‘Smart alarms’ can be selected which limit the reversing signal to 10 dBA above the ambient noise level, thus reducing intrusiveness (particularly at night).
  • Identifying the optimum placement of waste dumps, location of haul roads, location of fixed plant such as crushers and loading hoppers. Waste dumps, stockpiles and the like can be used to shield fixed items of plant which generate noise.
  • Eliminating tonal, impulsive or intermittent noise emission characteristics. These characteristics are more likely to cause annoyance because the likelihood of complaints is less for a continuous broadband noise than for one which is intermittent and/or tonal. Tonal components are often due to a fault in the machinery and may be eliminated by appropriate maintenance. Advanced control systems allow for switching between audible alarms during daytime operations and light alarms during the quieter night period. Using flashing lights for alarms will eliminate intermittent and impulsive noise generated by audible alarms.
  • Providing sound walls and acoustical screening. This option is generally effective when plant is operating at ground level in close proximity to the bund wall. Also, earth embankments can often be constructed from overburden and materials from stripping and initial excavation works, and provide an alternative means of stockpiling soil for future rehabilitation works. However, the use of bunding becomes less effective as the distance between the bund and the noise source and receiver increases.
  • Incorporating optimum buffer zones and setback distances. This is most effective where large distances are involved. In general, doubling the distance between the source and receiver will result in a 6 dBA reduction in noise level.
  • Acoustically treating dwellings. This is generally seen as a last resort, as the overall reduction achieved often does not justify the cost involved. Also, no improvement in outdoor amenity is achieved.

Low-frequency noise can be particularly difficult to mitigate because of the long wavelengths involved. All building materials attenuate higher frequencies more readily than low frequencies. Massive building elements such as concrete walls, or drywall type construction with large air cavities, will be required. Ventilation openings are likely to be a particular issue, as most louvres and attenuators struggle to make any impression on low-frequency noise. Specialist advice should be sought for the design of enclosures around equipment with significant lowfrequency components, such as pumps, crushing circuits, screens and large motors.

Measures commonly adopted to control the impacts of airblast include:

  • reducing the charge mass
  • increasing/optimising the stemming height and ensuring the type of stemming is adequate
  • eliminating the exposed detonating cord and secondary blasting
  • orientating faces away from potentially sensitive receivers
  • using a hole spacing and burden which will ensure the explosive force is just sufficient to break the ore to the required size
  • applying best practice design of the blast initiation sequence and timing delay (see Section 4.5)
  • providing optimum buffer zones and set-back distances for sensitive structures
  • acoustically treating dwellings.

CASE STUDY: Noise-suppressed surface exploration drill rig

For many years, a company has struggled to fully drill out its exploration leases, because of the noise restrictions involved with operating machinery in a builtup urban area. The company has experimented with many forms of noise suppression, including surrounding rigs with shipping containers and large hay bales, erecting sound walls, and even digging large pits for the drilling rigs to work in. These measures all had some degree of success but were far from ideal.

In 2007, the company purchased an Atlas Copco CS14 drill rig, with the intention of enclosing the unit within fully noise-attenuated containers.

The drilling department identified the need to make the system modular and self-contained. Six sea containers were used—four on the ground floor and two for the mast of the rig— to encapsulate the entire worksite. Everything, including drilling fluids, tools, drill rods, power generation and even the crib room, was enclosed within the system.

After consulting acoustic engineers, the company decided to use a mixture of noise attenuation products on the walls of the containers to reduce noise both internally and externally. The noise attenuation products included sound-deadening paint, 50 millimetre sound-absorbent foam and a 6 millimetre nylon sound barrier.

The combination proved to be extremely successful, reducing noise emissions from 110 dB at the machine to a measured 52 dB immediately outside the containers and 38 dB measured at 200 metres. With a 30 dB reduction inside the containers, the noise attenuation was celebrated as a great win in terms of operator comfort and safety.

The containerised rig has successfully completed six months of 24-hour drilling at two sites, both within 200 metres of residences. To date, no complaints from the surrounding neighbours have been received.

Share this Page