Memoirs of Drilling - 2

Memoirs of Drilling - 1

Now that everybody has used the video to get a great night's sleep, I'd like to focus on some highlights. When I first came to the big company, we had a Geotechnical Engineering Department. This was a very busy place, since we were actively building at the time. Our department was always in conflict with the Civil Eng. Dept., because they would use the drilling results to design foundations. We, of course, thought it was our right to comment on their designs!

At about that time, Darlington was just a big field, and Geotech was the first to go in. In those days (and now!), they just picked the site, and we had to put on a nuclear plant, by jimminey!

The first thing was to lay in a site grid by the surveyors. Over the course of constructing the plant, there would be several grids, which made things hell, if you ever wanted to plot all boreholes. Now, everything is GPS. It is extremely important to locate every hole with accuracy.

At Darlington, we would go in first with soil drilling. This was the standard hollow-stem auger, probably on a track-mounted drill, because of the mucky conditions. The auger would be drilled down every few feet, and then a sample taken. That would comprise of removing the centre plug, and attaching the split spoon. I always loved the soil drilling, since the smell of the deep soil was magnificent! A good geotechnical engineer could tell the type of soil, by listening to the effort of the drill, and mushing the soil in his hands. You would grind the soil between you fingernails to check the silt content.

Unfortunately, you didn't want to stand there for hundreds of boreholes, so you had to rely on the drill logs. The sampling would consist of a split spoon, which was a split cylinder held together by rings. This would be attached to the central rod and lowered into the hole. The most important thing (IMHO), would be whapping the sampler into the soil below the auger. This was done in a very controlled manner, using a standard steel weight, dropped a standard distance. The number of whaps to driver the sampler in, was the N-Value. Although a crude measure, it had the advantage of being done a million times all over the world, and for all sorts of projects. For example, the odds of soil liquefaction during an earthquake can be correlated with N-value.