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For marsh coring, I am interested in an easily portable coring solution that can give me rapid and perfect core recovery for 0-3 meters depth.  Additionally, only a small crew of three people should be necessary to operate and carry the gear so it can be used for rapid exploration. While a vibracorer might be thought of as the optimal tool for a marsh environment, it definitely isn't something one uses for rapid exploratory work.  The gouge auger, on the other hand, is the epitome of portability and rapidity, but the recovery is not perfect, cores are limited to 1 meter length sections, and sample size maxes out at 6 cm diameter cores.

I have developed a technique for taking undisturbed, 2-3 meter long, wide diameter marsh cores that gives me perfect core recovery, and is extremely portable and rapid. Recently, I used this technique to take 8 cores (2 m length) on a 50 m spaced grid, and we accomplished this in just four hours using only three people! I use "Schedule 40" PVC tubing because it is sturdy, but I'd eventually like to try it with thinner-walled drainage tubing which is lighter and cheaper.

To get perfect recovery, I use both a core catcher and an expandable piston to provide suction.  For info about making the core catcher, see the "Steps for preparing a 10 cm diameter PVC tube with a core catcher" section below. For info about the expandable piston I use, see the "Expandable piston for suction" section below. For a brief description of driving the PVC into the ground, see "Driving the PVC" section below. For info about pulling these long, wide diameter cores out of the ground with just three people, and a minimum of effort and time, see the "Extracting Cores from the Ground with a Mechanical Advantage" page.  To see some typical results, jump to the "Sample 10 cm diameter marsh core" section below.

Steps for preparing a 10 cm diameter PVC tube with a core catcher:

1. get your "Schedule 40" PVC tubing and shim metal stock (steel); sources for shim stock include Lyon Industries and Precision Brand; preferably go for the 12" wide rolls because if you use the 10 cm (~4 inch) wide core catcher template I have provided below, you can get three strips out of it
2. gather the following tools:  two "Vise-Grip" style pliers, an electric drill with an 1/8 inch bit, a pop rivet gun with 1/8 inch diameter pop rivets, a tool of your choice to sharpen/bevel the PVC tubing (I normally use a coarse sanding disk since I have the electric drill out anyways), tin snips to cut the shim metal, wire cutters, and a sheet metal bender (if you happen to have one of these)
3. cut your core catcher from the shim stock using the tin snips; I have constructed a template for 10 cm diameter PVC tubing which you can download as corecatchertemplate.pdf
4. fold the core catcher along the "fold axis" line about 45°; if you have a sheet metal bender, this is easy to do, otherwise you'll have to improvise
5. sharpen the end of the PVC tubing with the coarse sanding disk (or tool of your choice) by beveling off about 1.5 cm of it from the outside surface to the inside surface of the tube; basically, you are just sharpening the end of the PVC tubing; a picture's worth a thousand words here--see the images below
6. using pop rivets, fasten the core catcher inside the PVC about 1 cm up from the base of the tube; you need the two vise-grips to get this done if you want to maintain your sanity; basically, you have to work progressively around the core barrel putting in one rivet at a time; start with the "untabbed" end of your core catcher since the "tabbed" end will get a double rivet at the end; use closely spaced vise-grips (separated by just 1/2 inch or less) to hold the shim metal flush against the inside of the PVC; drill an 1/8 inch hole through the PVC and shim stock between the vise-grips, and fasten with an 1/8 inch diameter pop rivet (smooth surface of rivet on inside of core); move the vise grips over about 2.5-3.0 cm, and do the same thing there; progressively work your way around the tube adding rivets; use a double pop rivet in the "tab" at the end
7. cut off the overhanging portion of the pop rivets on the outside of the core barrel with wire cutters

I do not have pictures of the whole process yet, but will prepare them shortly.  For the moment, the images below give you an idea of what I am talking about.  Unfortunately, they are from one of my earlier attempts when I had the core catcher legs too wide, and left out the bending step (number 4 above) until the end.  But they illustrate approximately what you should have when you are finished. Once you have the core catcher actually cut out from the shim stock, you can complete the remainder of the process in about 30 minutes.  Though this process is for 10 cm diameter tubing, you can easily adapt it to other sizes. Clicking on the thumbnails below will pop up larger images.

Expandable piston for suction:

On analogy with an expandable rubber piston that provides suction for various lacustrine piston coring systems, I purchased some 2.5 cm thick, 10 cm diameter neoprene rubber disks to make a similar piston for the PVC tubing. I purchased this at a local store (http://www.flnmar.com/), but you should also be able to find it in your area.  Our Departmental MacGyver, John Sweeney, was able to build an awesome expandable piston using these rubber disks (see pics below).

Once the PVC has been hammered into the ground, I insert the piston into the top of the PVC as far as it will go using the simple piston pusher/puller John built. Basically, this piston pusher/puller is just a double nut on a threaded rod--I can screw it on to the threads at the top of the piston to push/pull it as necessary.  Once in position, I use a standard 3/4 inch socket wrench on a extender handle to tighten up/expand the piston.

After tightening up the piston, the whole core is pulled out--see the "Extracting Cores from the Ground with a Mechanical Advantage" page for how to do this. At this point, I loosen up the piston with the socket wrench, and then pull it out with the piston pusher/puller.

This piston provides incredible suction--in one case where a core catcher was essentially turned inside out, the piston provide enough suction to retrieve the whole sediment column with the exception of the lower 20 cm which broke off!

As an engineering note, notice the thick plastic/teflon washer at the top of the piston. Our first piston design did not include this. So, when we went to tighten up the piston, at a certain point the surface friction between the tightening nut and upper metal disc became greater than that of the piston against the tube walls.  Thus, the whole piston array would turn inside the tube, and it would never expand sufficiently. That's where the thick plastic/teflon washer comes in--it prevents this from happening.

There is no actual designs or plan for the piston--it was basically built on the fly.  But here are some images to that show you how it is built so you can attempt your own. The first four images are the piston itself with views from the top towards the bottom.  The fifth image is the piston pusher/puller mentioned above. Clicking on the thumbnails below will pop up larger images.