Driving Well Points
I'm curious about methods of well point installation being used nowadays. I never paid them much attention, when they were popular, a generation ago in this area, when a regional drought sent homeowners in search of ground water to keep their lawns green. Most of them seemed to be installed with simple drop-weight rigs. I assume there was a drive cap atop the pipe being driven, with the vent hole enlarged, if the drop weight had a alignment rod projecting from its bottom.
I know that augering would be preferred over pounding in well points, so the soil could be examined, although most of the likely sources I see are in thick layers of gravelly sand, courtesy of the moraines, from the last ice age. In those, I could pound a point, and not concern myself too much with the soil.
What I am wondering about, though, is whether a point-pounder has to worry about the pipe he'd use on a point installation. Most of the galvanized pipe I see is rolled and seam-welded. I could swear it's lighter than the old stuff. I've read one thread about a point pounder discovering the pipe had bowed outward from the impact. That would be in keeping with my misgivings about the modern pipe. I suppose one could use sch 80 pipe.
I've seen one machine that looked like it could do some serious point pounding. It was designed to raise and drop a hollow cylindrical weight, to strike a steel disk laid atop the drive coupling, with the pipe threaded into the top of the coupling keeping the drop weight aligned. I think the machine was for getting soil samples near highway construction, since it could also hammer a point back out of the ground, if another drive coupling and steel disc was set in place above the drop weight. If I were to create a point-pounding rig, I might use that machine as a model.
We built a small point pounding rig years ago. It had a motor that ran a hydraulic pump that was tied into a cat head. The derek was about 7' high. We built it for this one specific job where we had to pound in a 2" well to 55'. Conservation would not allow any heavy drilling equipment on this guys property and we knew there was allot of layers of gravel for the first 25'. We used it allot in spots where you couldn't get any drilling equipment. That hammer that you were talking about for soil samples would work but what's even better is the drive weights with a hole through the center that allows the weight to move up in down. We used 300lb. hammers like that to drive 3 to 6 inch casing when we were test drilling. I wouldn't suggest that amount of weight to drive a 2" well point but a hammer like that with less weight is the way to go.
About what weight were you using on the 2 inch point? Did you ever see any issues with pipe deformation from the pounding?
One thought that occurred to me while I was looking over the sampling rig, was that having an additional length of pipe attached might allow for an air compressor to be connected to the pipe, with an eye towards monitoring airflow through the point, as an indicator of how free-flowing the soil is.
Here in eastern NC coastal area where we usually only have to deal with sand and a thin layer of clay or two, we hand-drive shallow wells (25' or less) with "3 joints and a point". The 5' joints are 1.25" galvanized pipe threaded on both ends. The points can be 3', 4' or 5'.
We use a home-made welded T-shaped hand driver with a concrete-filled piece of capped 6" steel pipe about 10"-12" long as a driving weight where the T crosses. The "handles" are about 2' each and the center guide pipe is about 3' long. One man or two men can drive wells with it.
We use a Schedule 80 black iron coupling tightened on as tight as we can for a drive cap, and then remove it, wrap the threads with teflon tape, tighten on a regular galvanized coupling, screw in the next section as tight as we can, and then do the next the same way.
I've helped drive a number of wells just like this, and I've seen them washed down with a long PVC pipe joint (easier), and I've seen the pipe and point sections just pushed down with the bucket of a front-end loader (easiest).
There are all kinds of ways to git 'er done, but I thought that I'd add this method to the mix for those who could use it.
Its been so long since i have driven one but i believe it was a 200 lb. hammer. If you encounter a boulder while drilling the point can walk off the boulder and cause the pipe to bow out. Its way important to keep each section straight as your pounding. The smallest inclination can cause a coupling to crack. That compressor set up sounds legit but your nipple on the drive coupling is constantly coming loose as you are hammering so unless you stop and tighten that coupling you would be losing allot of air while you were driving.I have never tried it but it makes sense. Allot of times i would fill the casing with water in between lengths to see how quickly the water would settle and that would give me a basic idea as to what the consistency was. Most of the wells that i drove were in areas where you knew you could get the water as long as your were 10 to 20 feet into the water table. For instance most of Cape Cod and Plymouth MA has a huge deposit of coarse sand and as long as your beyond the water table that 10 to 20 feet with a 10slot screen your good to go. In other areas the wells need allot of developing because of the silty fine sand and clay lenses in the ground. Those are the areas to drill in if you want to learn all about developing and screen sizing. In one spot we drilled a couple of six inch screened wells that supplied irrigation to a soccer field. We set our screens 30' into the water table but because the material was so inconsistent we had to develop those wells for 2 days before they produced what we were looking for.The biggest problem that we had was that the company that we subcontracted to drill one of the wells used revert(type of drilling fluid) to keep the hole open and it plugged up the zone we were trying to pull water from. We actually sent soil samples out to Johnson Screens and they told us that we wouldn't get the water we were looking for but we pulled it off.
I figure underground rocks and boulders are pretty much an insurmountable barrier, and I might have to try another spot. (the reverse hammering of that sampler rig would help extract a point) I suppose an inch-and-a-quarter point would require a lighter driving weight than 200 lbs. I'd still have misgivings over the modern galvanized pipe, but I guess I'd have to try a few points to be certain. What I am certain of, is any complaints about pipe deformed from pounding would probably bring back a reply that it wasn't designed to imitate a nail.
It almost seems that the humble 2-inch deep well kind of falls between the cracks. An auger that could quickly drive down over fifty feet would probably need 2-inch auger shafts as a minimum, and that leaves no room for fluting to bring material up. I'm not looking to chase deep water, but I wouldn't mind the capability, if I ever did cobble together a pounding rig.