Enviromental sensitive areas

Environmental constraints

The major environmental constraints which normally apply to rockbreaking in environmentally sensitive areas are airblast overpressure, noise, ground vibration and fly rock limits.

Airblast overpressure

Airblast overpressure is caused by air-transmitted vibrations or compressional waves produced by the rapid expansion of explosive gasses and the rapid movement of the rock, resulting in the sudden displacement of the air surrounding the blast. Overpressure levels produced by NxbursT™ are low when compared to conventional explosives and are of a shorter duration and less damaging frequency. This gives NxbursT™ a major advantage over explosives in environmentally sensitive areas.

Noise

Noise is the part of the airblast overpressure wave which falls within the audible frequency region of the human ear. The high frequency portion of the air pressure wave is audible and is responsible for the noise that accompanies a blast. The lower frequency portion is not audible but can excite structures, such as windows, which in turn respond and produce secondary noise such as rattles.
A well-stemmed NxbursT™ cartridge in granite will generally produce a noise level in the range 80 to 85 dBL at 50 metres from the hole.
Noise levels can be attenuated by the use of conveyor belting, or other matting, to cover the holes being fired.

Ground vibrations

Ground borne vibrations from blasting can cause damage to buildings and infrastructure which are in the vicinity of the blast. The degree of vibration induced damage caused by blasting is dependent on the magnitude, frequency and duration of the vibration. The vibration signature produced by the combination of high frequency, low duration and low magnitude vibration waves enables NxbursTTM to be used in close proximity to vibration sensitive sites where conventional blasting is prohibited or impractical. A NxbursT™ specific vibration equation has been developed from monitored data collected from several NxbursT™ rockbreaking excavations in sensitive civil applications.
These data have been collected by an independent group to produce a practical graph which relates vibration levels (“PPV”) to charge weight and the distance from the shot at which the vibration is being measured.

Fly rock

A NxbursT™ cartridge produces an optimal pressurisation of the hole for a given burden and type of rock. By controlling the characteristics of the pressure pulse, the velocity and distance traveled by the dislodged rock can be limited. Controlled gas release from the NxbursT™ cartridge, at a relatively low pressure, results in a minimal quantity of low velocity fl yrock, which is generally contained within 10 metres of the rockbreaking event.