Rock Blasting

Rock blasting involves using explosives to shatter, break or split rock making it easier to remove in smaller more managable pieces. An ancient method for splitting rock was to heat the rock by fire and pour water on it, this sudden cooling and contraction would cause the rock to split. Homeowners with problem rocks on their property can use this method to get rid of large rocks. Modern methods use explosives and boreholes which are usually drilled at calculated spacing to control the blast. Location, depth and spacing of the holes depend on the local environmental conditions and the nature of the specific job.

In rock removal, using explosives is called "shooting." There are blasting systems availabe that it enables homeowners, contractors, landscapers and farmers to safely smash and remove boulders. These fairly simple systems make less noise than a 22-cal. rifle and are so safe you don't need a federal blaster's license.  
 

Presplitting
Presplitting is a technique where a specific area of the blast site is prepped before drilling the rest of the boreholes forthe main blast pattern. In presplitting, a row of holes is drilled along three sides of the main blasting blocks and charged with fewer explosives and less powerful explosives then what will be used for the main production blast. This creates afracture line along the desired break, and exposes the half barrel of the blast hole after excavation. Presplitting is seldom used in underground work but works very well in open areas.

Line Drilling
Line drilling is one of the earliest controlled blasting methods and involves creating a plane of weakness by drilling small diameter holes along a predetermined control line. Drillers space the holes closely and drill along the excavation line inexpectation the final blast line will accomplish the desired result. Line drilling reflects some of the shock waves of the blast, reducing shattering. This technique allows the host rock to maintain a lot of its strength and integrity but is quite expensive due to the high drilling costs of the closely spaced holes.

Smooth Blasting
Blasters and larger blasting companies mainly use smooth, perimeter or contour, blasting in underground applications. An ideal smooth blast causes minimum damage to the host rock which leaves it structurally sound. Blasters drill holes in the roof of tunnels and headings, parallel to the direction of the excavation and space them closely. They are then loaded with decoupled charges which are fired simultaneously and produces a smooth and sound surface.

Cushion Blasting
Cushion blasting is when workers have to trim excess material from the final high wall. They drill holes in a single row along the excavation line, usually between 2 and 4 inches in diameter. Blast holes have small, well-distributed charges and are completely stemmed. Workers perform cushion blasting after the main blast has been excavated. By firing cushion holes with minimum or no delay between the blasts, the detonation shears the rock web between the holes and produces a smooth wall with minimal over break.
 

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