Thursday, October 20, 2011

Geoprobe Work

On occasion we oversee geoprobe investigations. Geoprobes developed as a less costly means of collecting soil samples for geotechnical and environmental purposes. Under the right geology circumstances they are a great approach for getting sub surface information. Essentially they are a hollow tube pushed into the ground and then pulled out with a sample of soil inside the tube. The wonders of hydraulics and extremely tough alloys do the trick.

Truck mounted geoprobe

Pushing the probe into the ground

Small tractor like rig. These types of rigs are great on steep slopes or inside buildings

Samples are collected in plastic tubes that can either be hauled back to the office or cut open at the site for sending off for chemical analyses. 

On a recent project we probed through an upper unit of sand and gravel (fill) down into Bellingham Glacial Marine Drift. The Bellingham Drift was deposited towards the late stages of the last glacial period when the Puget ice lobe retreated out of the Puget low lands. The mass of up to 6,000 feet of glacial ice had pressed the local earth surface downward. As the ice retreated the sea flooded over the land that had been pressed down by the ice such that the ice lobe was for a time floating on inland sea. The melting ice rained a steady load of finely ground rock silt and clay onto the sea floor below as well occasional pebbles, cobbles and boulders. This phenomenon was most pronounced in the Bellingham area as the ice had been thicker here than areas to the south and the glacial ice lingered longer in this area; hence, the name Bellingham Drift.

Where the drift has remained saturated it is very soft - a bit stiffer than tooth paste. A bit of a challenge for constructing big heavy buildings but pretty good at preventing the movement of contaminants as long as it is the silt/clay variety of the drift. 

Geoprobe core samples of soft Bellingham Drift

I have a habit of making balls out of the extra sample material.
More skilled geos might shape figures 


Dude Diligence said...

Probing has its limitations and it's good to know beforehand in what conditions it'll be successful and where you won't. The best thing about it is that you generate very little spoils. I recently had that 54LT (Cascade) inside a building and only managed to get down 4 feet (Vashon till). Geologic Drill Exploration has a nice limited access auger rig mounted to a Bobcat and I'd wished I'd used that instead of the probe.

Dan McShane said...

It is always great when it goes smoothly and a bummer when it doesn't. We have been on a good streak of late other than the rig breaking down on one recent project that was luckily for us very near home.

Geoprobe for sale said...

Thanks for posting so many pictures of what it looks like to use a Geoprobe. You're absolutely right, the smaller track-mounted units are great for unique job sites on hills and inside buildings. For years we only drilled with truck mounted drills, but have found numerous uses for the smaller units. Thanks for sharing.