Field of application

Blasting techniques are essentially applied to rocky materials.

Blasting may serve several purposes:

  • excavating or leveling out rocky massifs
  • stabilizing potentially unstable rocky areas
  • excavating or expanding underground works (wells, tunnels…)

Basic Principles

Blasting consists in fragmenting rocks by inserting explosives in a drill hole. Although a single charge may suffice to fragment a simple block, rocky massifs require more or less closely-packed multiple charges.
Two types of energy come into play when using explosives:
– the shock wave;
– gas pressure.

Different types of explosives

There are two main types of explosives:

  • deflagrating explosives (black powder)
  • detonating explosives (the most common kind)

There are three main groups of explosives:

  • dynamite: a nitroglycerine-based product, it is suitable for massive rocks
  • ANFO (aluminum nitrate – fuel oil): larger quantities of this explosive are needed as it is less efficient. It should not be used when the rocks present cavities
  • emulsion: this explosive may be used in a number of ways and therefore has a relatively wide field of action.

Explosives ill only work when associated with a detonating device and a priming device (pyrotechnic, micro-timed electric, electronic (sequential) or non-electric detonator).

Explosives are classified according to various parameters :

  • detonation speed: it is the speed at which the reaction process propagates in the mass of the explosive
  • critical diameter: it is the diameter under which the explosive will not detonate
  • specific energy, which is the sum of the gas-generated energy and the shockwave-generated energy
  • density
  • sensitivity to priming
  • water resistance

Firing plan

The firing plan is a document that must list certain elements of information elaborated by the engineer:

  • firing location
  • drilling characteristics (diametre, depth, inclination, number of drilled holes, CUI – single-detonation charge…);
  • characteristics of the device including type of explosive, priming, packing…
  • priming sequence

Drilling

Drilling operations matter because they will determine the quality of the firing plan.

Philippe’s advice about Blasting :

“Pre-zoning detonations make it possible to individualize the masses to be mined and hence limit the impact of Blasting on the non-excavated areas bordering the zone of activity.”

Caution measures relative to Blasting

Blasting is often a quite impressive technique that may generate a number of risks and nuisances which can be perfectly controlled if the company undertaking the works is competent.

  • Provisions can be made for trial detonations in order to validate the CUI (single-detonation charge
  • Vibration recordings may be carried out in order not to exceed the noise threshold criteria
  • Protections against projections may be installed (geotextiles, wire netting…)