Memoirs of Drilling - 3

Memoirs of Drilling - 1
Memoirs of Drilling - 2

In addition to the N-value, the split spoon brought up a soil sample. This was important to tell if it was silt, sand or clay, or any combination. In this type of till, the real nasties are sand lenses. It didn't really matter at Darlington, since we were so traumatised by the sand lenses of Pickering, that we decided to take off all the dirt.

That was 100 feet of dense till. The operation was magnificent, with these huge scrapers, which then dumped the dirt on Darlington Hill, which can be seen from the highway. But I digress. The soil augers told us where the bedrock was, simply because you couldn't drill any more.

The soil augers were great for the dirt work, but since it was getting stripped off, we needed to find out about the bedrock. That was the time to bring out the diamond drills! We either slipped a casing on the soil hole, or sunk a new casing to bedrock. This was required to keep the hole clear for rock drilling.

Although I loved the dirt, the rock was where the action was! Here's a Wiki thing that I started. The process seems a bit tricky, but the drilling part is merely a pipe with a tip embedded with industrial diamonds. As the drill stem turns, water is injected in the middle. The diamonds chew up the rock to a powder, which is then washed away. Since the pipe and drill bit are hollow, a core starts to form up the middle.

All the remaining complexity is then devoted to keeping the core as well-preserved as possible. If you are in solid rock, and just looking for minerals, you can just lower in a core-breaker-grabber, and yank out the core of solid rock. For geotechnical drilling, you can have a very fancy triple-tube arrangement which produces undisturbed core, with all it's gaps and fractures.

We drilled the bejeezus out of Darlington, because we were doing all sorts of work in the rock, including tunnels. We even put in a couple of exciting 'deep holes' to look at the granite beneath the limestone. Those were fascinating, and a possible subject for another story.