The Dynamite - John Dunn, Consultant, Ambertec, P.E., P.C.

My boss had built his home at the very top of a multi-hundred foot hill in New Hampshire and true to that state's reputation, the hill was largely made of granite. He decided one day to add an extension and to do that, he had to extend the foundation. He got an architect's instructions about how to proceed.

The project involved removing of a lot of granite from right outside the kitchen door. I had volunteered to assist in the process which consisted of drilling a set of properly spaced two-inch diameter holes into the granite, loading each hole with a stick of a dynamite into which a blasting cap had been inserted, wiring the caps in a series circuit and setting them all off with a shot of 120 VAC line voltage.

I had helped to drill the holes using a special rock drill which was like a jackhammer with a rotating bit.

A table of dynamite grades had been provided by the architect. It listed for each grade, the maximum outbound particle velocities at a dynamite stick's surface. The velocities were given in some prosaic units, maybe in inches per millisecond, although I don't really remember. What I do remember was translating the chosen grade's number into an outbound particle velocity of ten thousand miles per hour. That was a measure I could relate to.

Just imagine the energy involved in accelerating anything from zero to that speed in a distance of less than one inch and realize that it was only a medium grade of explosive, right in the middle of the chart.

 
The blasting caps were timed. They had explosive delays of zero, 1 mSec and 2 mSec. The idea was to put the dynamite with the fastest caps into those holes that were farthest from the house. Then when the exploded debris of those first charges went up and was still in the air, the later charges going off would force the bulk of the debris to be blown away from the house. It worked.

After each explosion, I helped remove the now broken blocks of granite by operating a backhoe. It was an odd sensation of power to have this mechanical arm moving five hundred pound granite chunks at my bidding merely by my pressing a few levers.

The project was a success.

 

Comments

[William Ketel]

I really can not imagine using dynamite right next to a house, unless the goal was to demolish the place. Your boss is amazinly fortunate that nothing bad happened.

[Joe Leikhim]

There are now demolition compounds that you simply pour into the holes and through expansion, fracture the rock away. I became interested in this stuff because some homeless guy in Santa Monica California made an explosive device from this non-explosive and it hurled a 300 lb chunk of cement and pipe 25 feet into the air. He is currently in jail by the way.