Drilling

The drill we are using is called a 75 CME which is essentially the size of a tow truck. It weighs about 36,000 lbs, the equivalent of 20 tons. These are heavy trucks. Ours got stuck in the sand at one of our bore hole points. A bore hole is essentially with a foot diameter and it goes however deep it can or needs to go.

The above picture is pretty close to what I’ve been working with. The only exception is that the drill guys weren’t fully geared up. All they had were hard hats and steel toed boots (and of course safety glasses if we were on the mine site). A second vehicle usually accompanies the tow rig: a water truck.

So, the first thing we do, or they do while I get my notes and tools ready, is lay out five foot long ogre drills. They connect with bolts, drilling deeper and deeper. I get ready some monkey wrenches, my handy dandy hammer, buckets, bags for the samples, my notes to be written, camera (if you can’t figure it out, I have to get a bunch of stuff ready). As samples are given to me of the soil, I’m analyzing it using USCS specs. I determine out in the field if it fits one of the major categories: silt, clay, sand, or gravel. Then I have to narrow it down from there. The picture below is a much more detailed overlook of what I’m doing. I think I should print it off and take it to the field with me

For this particular job, we ogred down to about 2′, then took a modifed california sample (Cal for short). The cal takes an undisturbed sample. It gets attached to the end of a center tube going down through the ogres (the ogres are hollow) and a hammer is placed at the top. I think it’s a 10lb hammer, but I’m not sure. It pounds so many times. For a cal, it can only be hit up to 80 times per 6 inches. After that’s completed, they give it to me, I break it open and then cap each of the three tubes inside (if there’s dirt in all three tubes). We did this twice, then we moved to split spooning.

Split spooning is with a long metal tube about an inch wide. It has a sand trap at the bottom to keep sand from falling out of the tube and back into the hole. The split spoon is set up the same way that the cal is set up. However, the hammer can only hit it up to 50 times per 6 inches.

Starting to sound complicated, right?

After split spooning, if we hit bedrock, we cored. Coring uses water, which is why there’s a water truck. This is where I get to sit around and watch because it takes a bit to core. They take the drill ogre out and then lower in these hollow metal tubes, one of which is a 5 foot sampler. They fill the hole with water and then it spins really fast. Has it spins, it cuts into the rock, taking a hopefully solid sample. All I do, is note the recovery of how much core we get per five feet and then the time it takes. Then I stash it in a box and take a picture with a ruler for scale.

This is what I have been doing for the last two weeks.

Next week, I’ll be doing straight coring from the sounds of it. We’re suppose to go down to about 120 ft for 4 holes. We are also doing a test I haven’t done before. It’s a perculation test, but on a much grander scale. I’ll talk more about that later once I understand it better.

For more information:

Drilling and Sampling — this has some more information concerning the equipment used for sampling as well as information on methods.
Bear Lake Methods: Coring — a site about coring. Not exactly what I was doing, but still interesting.
Boring — an article explaining boring better.
Geotechnical Investigation — a better explanation or summary of what I’ve been learning/doing since I’ve taken this job.

…to some of you this may appear extremely dull. But to me, this is definitely the thing I wanted to be doing when I finished school.