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MAXAM Foundation

MAXAM Foundation - MAXAM Chair - Blasting solutions - Profilometry and deviation measuring in designing blasts

Most blast benches are irregular due to the complex combination of the in-herent 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, thus requiring specific actions when planning the blast in order to ensure optimal results.

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

Measuring the geometry of the blast bench

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

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 allow-ing full recognition of the bench and not just the free face.

Measuring is done for several reasons: • To ascertain the actual 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).

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

Blast hole deviation measuring

Early identification of possible drilling errors allows the charging plan to be adjusted, thus avoiding any risks. Measuring possible deviations between the design and the actual situation of the blast holes is required once the front has been drilled. 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 minimize 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 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 the 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 process in blasting operations in quarries, in order to ensure optimal use of the explosive energy and minimize possible effects such as projected material, vibrations and blast waves.

Be sure to contact MAXAM if you would like to add value to your mining project through the use of profilometry and deviation measuring.

Blasting Solutions. May 2018


Last update 2020.09.21
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