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Articles from DRILLING RIGS (158 Articles), BLASTING & EXPLOSIVES (156 Articles), BLAST MONITORING (120 Articles)

Measuring profilometry, deviation in blast design

Most benches are irregular due to the complex combination of the inherent structure of the rock mass, its geomechanical condition and possibly damage caused in the free face by the previous blast.

These factors make up a three-dimensionally variable free face, requiring specific actions when planning the blast for optimal results.

Since designing the blast consists of optimally distributing explosive energy in the rock mass, correctly measuring the condition and geometry of the bench and precisely determining the blast holes is key to ensuring the results are as accurate as possible.

Knowing the geometric condition of the bench is hugely important when designing the blast. This allows both the height of the bench and the presence of banks or caverns in the free face to be determined, among other parameters.

Profilometry is a key tool for ensuring detonations for the first row and the overall blast are undertaken effectively.
Profilometry is a key tool for ensuring detonations for the first row and the overall blast are undertaken effectively.

A range of different technologies and measuring instruments are available for digital modelling of terrain. Laser profiles (2D or 3D) have traditionally been used for measuring blasts in quarries, although drones are now emerging as a more economical and precise alternative, with the additional benefit of allowing full recognition of the bench and not just the free face.

Measuring is done for several reasons:

  • To ascertain the profile of the bench before designing the blast.

  • To improve the environmental efficacy, safety and conditions of the blast (reduce projected material and vibrations/blast wave).

Digitising the bench’s geometric model allows the blast to be designed using specialist software such as RIOBLAST. Blast hole mouths, angles and directions are determined to ensure optimal distribution of explosive energy.

Profilometry is not only a risk management technique that can determine the blast wave and avoid or minimise projected material, but it is also a key tool in ensuring detonations for both the first row and the overall blast are carried out effectively.

Early identification of possible drilling errors allows the charging plan to be adjusted, thus avoiding risks. Measuring possible deviations between the design and the actual situation of the blast holes is required once the front has been drilled.

Undertaking the blast hole measuring process via the laptop.
Undertaking the blast hole measuring process via the laptop.

Probes with inclinometers or compasses are used to ascertain position and depth. Although it is most commonly used in the first row of blast holes only (to minimise the potential risk of projected material and blast wave), extending the measurement to the entire blasting front is advisable.

The most common factors associated with the deviation mechanisms of blast holes are:

  • Structural properties of the rock mass (fracture planes, joints with materials of different hardness, etc).

  • Drilling diameter being very different to drill rod diameter.

  • Errors in alignment and starting point.

Apart from possible errors in the starting point, deviation throughout the length of the blast hole is a critical factor. This type of error may be associated with poor alignment of the machine, problems with equipment parameters or geological factors such as the presence of crevices or fracture planes, since the blast hole tends to accommodate the path of least resistance.

It is important that acceptable blast hole deviation ranges for all bench heights in each quarry or construction site are determined. This criterion must be established jointly with the drillers or the drilling contractor, and both must sign the blast deviation standard.

Joint measurement of the geometry of the bench and blast hole deviation is a fundamental stage in the continuous improvement of blasting operations in quarries, to ensure optimal use of explosive energy and minimise possible effects such as projected material, vibrations and blast waves.

Source: MAXAM Australia

Thursday, 21 February, 2019 06:38am
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