A local gas station has been undergoing remodeling, but one day it had geo-specialists pay a visit. On the left is a small drilling rig, and on the right is the typical panel truck used for cone penetrometry testing (CPT). It’s propped up on stout legs to make a stable platform, and as I peeked underneath I could see the penetrometer shaft sticking into the ground like an ovipositor.
CPT consists of pushing a steel shaft with a standard cone-shaped tip straight into the ground. Sensors
on the truck measure how much power it takes to do this in the tip measure the pressure, which varies as the tip penetrates different types of soil. Sensors in the tip also measure the electrical conductivity of the soil, pore-water pressure, and other things. In deep ground like this part of Oakland, a CPT tip can be pushed hundreds of meters down, but here they’re probably going down no more than 10 or 20 meters, just deep enough to see if the underground fuel storage tanks will be stable there. In chronically wet ground, empty tanks have been known to rise out of the ground during, say, earthquake shaking. Learn a little more on my About.com site.
This is hardhat work, but it’s not very dirty. Geotechnicians can get steady and varied work doing CPT with no more than a high-school education. The crew of this truck included a woman, too.
By the way, I have entered the “Blog Your Way to Antarctica” contest, which runs through September. Please see my entry here, and if you like the idea, give me a vote—the earlier the better. I know it would mean a break in this blog, but I’d make it up to you.