Tools and Tips

Extracting cores from the ground with a mechanical advantage

Pulling cores out of the ground by hand was always one of the more demanding tasks until recently. Driven by difficult access conditions, and limited personnel and logistical support, I have generally avoided solutions such as tripods and winches because of portability. This was also driven in part by discreteness—coring already attracts enough attention, but on foreign turf it is preferable to remain as low profile as possible. So, I have always ended up pulling out cores by hand sometimes to the temporary detriment of the backs of field team members [sorry, Ugur :( ]. But pulling out a core by hand can become basically impossible when you reach 10+ meters depth with the gouge auger, or when you run through a cemented horizon. And with wide, 10 cm diameter marsh cores, they have so much surface area for friction, and suction is so great, they are often impossible to pull out by hand even after only ~50 cm of penetration.

So I've developed a portable and rapid solution to deal with this. This solution was inspired by coring master, Mark Abbott, who has been known to use a car jack for his lake work. Basically, I use a Hi-Lift jack (model HL-485) to pull a core right out of the ground. This style of jack is sometimes called a "farm jack" or "Jeep jack". Note that it is not the ubiquitous scissor-style jack you find in automobiles nowadays—those types just don't have enough run. The Hi-Lift jack has a rated lifting capacity of 2115 kg (2.33 tons). That means that just two (!) people can pull a 10 cm diameter PVC tube out of the ground with relative ease, even if it has been driven to a depth of 2-3 meters! See the "Marsh coring—portable, rapid, and perfect core recovery" page for info about cores like this.

To attach the core barrel to the jack, I use rubberized 1/4" steel cable. I originally thought I would need some type of lip or ridge on the core tube so the cable would catch, but experimentation shows it is not necessary. Make a simple noose-like loop in the cable. Now, with plenty of slack on the loop, double it over on itself twice so that basically the big initial loop is composed of three smaller loops. These three smaller loops should be big enough to fit around your core tube without much slack. By making three (or more) loops like this, the cable essentially functions as a boa constrictor—the tighter you pull on it, the tighter it pulls on itself and grips to the core tube. Then you simply attach the cable to the Hi-Lift, and start jacking it out. At the end of a run, just slip the jack and triple loop back down to pull out another 50 cm.

During the extraction process, the jack will have a tendency to pull itself over. So while one person is pumping the jack, the other will have to push on it to compensate the tilting, and keep it vertical.

To make the process go faster, you can use a cable grip. This is optional, but very helpful. The cable grip also helps keep the steel cable in good condition—otherwise it quickly becomes kinked and frayed which is brutal on your fingers. I use a Klein Tools "Haven's grip" (model 1604-20L). I attach it to the jack with a screw pin anchor shackle as seen in the pics below.

The pictures below show this system in action on a marsh with 10 cm diameter PVC cores, but this technique can be easily adapted to other coring systems like the gouge auger. In general, you will need to use a board or beam (like a 4x4) underneath the jack to distribute the massive downward force being exerted at the jack's base. If you don't, you will simply succeed in driving the jack into the ground as you try to pull the core out.

Clicking on the thumbnail images below will pop up larger versions.

Hi-Lift jack (model HL-485) with a shackle and Klein Tools "Haven's grip" (model 1604-20L)	a closeup of the cable grip	jacking a 4 inch (10 cm) diameter core out of Belle Isle Marsh (David Besonen at left, Pierre Francus at right)	core is about halfway out with just a minute's work, and no strained backs!
make a large, noose-like loop in your 1/4" rubberized steel cable	fold the loop over on itself twice to make three smaller loops out of the initial loop	the triple loop functions as a boa constrictor—the tighter you pull on it, the tighter it pulls on itself and grips to the core tube	triple loop seen from the side	triple loop seen from the back