Blasting is an important part of modern construction. It is predominantly used in fragmenting consolidated soil and rocks. Over the years, populations have grown in and around cities and encroached towards many construction sites. This has led to an increase in the number of public relations problems following the use of explosives in the construction. Controlled blasting comes in handy to reduce the negative effects of blasting. These effects include over-breaking, excessive ground vibrations, noise and fracturing on the surrounding rocks. Here are some of the techniques employed in controlled blasting:
Line drilling is a technique of controlled drilling where one row of closely knit holes are dug along a neat excavation line. The row of holes offers a perfect plane of weakness along which the primary blast can break, acting as guide to keep the plane of weakness from straying. To add on that, the row also leads to a reflection of some of the shock waves given off by the blast. This reduces stress and shattering in the surrounding areas.
One of the drawbacks of line drilling is the high cost incurred to make the holes, considering that the spacing is close. Most contractors need a percussive hammer for this purpose, which can be costly to hire or buy.
Smooth Blasting (Contour or Perimeter)
Smooth blasting is a technique often used when you are carrying out the blasting underground. The method requires holes drilled with close spacing and loaded with decoupled charges. The workers fire the decoupled chargers at the same time to produce a contour without causing fractures on the rock adjacent to or behind the face that you are blasting. Ideally, there is very little damage to the areas around the face that you are blasting as this technique localises the impact of the shock waves.
Trim or Cushion Blasting
Similar to line drilling, trim employs a single row of drilled holes dug along the excavation line that you want to blast. In most cases, the diameter of the holes used in this method range from two to four inches, and the holes are loaded with evenly distributed light charge for blasting. The holes are fired shortly after removing the main excavation. Firing immediately between the charges in the holes makes the detonation shear the web of rock between the holes. This produces smooth walls on the surface you are blasting with limited over-break to the surrounding.
A top benefit of this method is that it is cheaper than line trimming because the holes aren't tightly spaced. For more information, contact an explosives supplier.