Pond Boss Forums POND CONSTRUCTION Selecting a site Boring vs Backhoe for Soil Evaluation

I recently drove by a contractor that was boring holes along side a county road, so I stoped and asked him what they were doing. He said they were making soil evaluations prior to putting in an underground municipal water main. So I'm wondering if that kind of soil sampeling would be as good as excavating with a backhoe, especialy sense my new pond site is planned to be 20' deep. (maybe wishfull thinking). Has anyone used this method? Relitive cost?



http://s266.photobucket.com/albums/ii254/tmikeltn/?action=view¤t=pondpreperation11-25-07.jpg

The main (only?) purpose for testholes is to see what the different soil layers consist of at a potential pond/dam site. An auger would do just as good a job at this as a backhoe, given it could go deep enough. IIRC, the definition of "deep enough" depends on the pond/dam in question.

Virtually all excavators have a backhoe or trackhoe that they can use for testholes. My guess is that really long, robust augers are most often owned by utilities and perhaps municipalities for putting in really big telephone/electric poles. So it may be harder to round up an auger for testholes. I don't know how the cost for getting one to show up would compare to a 'hoe delivery charge, but they should be able to drill a hole quicker than a 'hoe can, hence presumably cheaper.

I used to have access to a small, tractor-mounted auger with a depth extension that would have been suitable for doing testholes down to about the 6 foot level. It's drawback was it had no reverse spin power, so if you hit a big root or rock and it locked up, you had to back it out by hand. The 6 foot depth would be OK for some pond projects IMHO but not for all. I assume that the large utility pole-type augers can go deepr than this, but I don't really know for sure.

oh my....it let me log in this morning....

tmk....if you have a relatively flat area to test, a small rig running hollow stem augers would get you more test holes in a shorter period of time than any other method. the purpose of the hollow stem auger is to allow a sampling device (usu. a split spoon) to be run through the augers and tehn driven w/ a hammer to collect undisturbed soil ahead of the bit. these soil samples can then be evaluated in the field and/or sent to a lab for geotech analysis......grain sizes, soil type, permeability, etc...in most deep soil areas (i.e. no bedrock present) a small hollow stem auger rig could easily go over 100 feet deep, so depth is not an issue. you could compare costs easily against a backoe by simply contacting local environmental or geotechnical drilling companies, telling them what you want, and have them bid.

in my experience, relatively shallow holes (<30 feet) should go around 10 to 20 per foot, maybe cheaper if the drillers can just backfill w/ drilled out soil and dont have to plug each hole w/ cement. plus lab costs if you send samples to geotech lab. total price could be a couple to several thousand dollars depending on how many test holes you do, but it would be the best possible information you could ever want and the investment might well be worth it if you want a nice pond that holds water for many years to come IMO.

good luck

DIED takes this one right where my first reaction originated when I read TMK's post; maintaining undisturbed soil samples. I was unaware of the hollow stem augur, but doesn't it still seem to be a bit too "hi tech" for pond field samples? The backhoe sampling procedure seems to be so simple and provides not only large lifts of undisturbed samples for research, but also allows one to control the hole width and breadth should it be necessary to get a "good look" at the big picture. Also, backfilling and compacting with a bucket to "pound it back down" in layers might provide a better final grade after sampling...? I will say, tho, that the augur is definitely arthroscopic when it comes to non-invasive sampling.

Thanks for your comments guys,

I did have a test hole dug this summer with a backhoe which was on my site just to remove some stumps. We could only get down about 12 feet. The hole filled up in just a few days and the blue clay went all the way down. The thing that got my attention about the boring opperation was the depth potential. Also my pond is planed to be about 400' long and I know soil conditions can change in that distance. As for the lab analysis on the soil, how about just handeling and visualy inspecting the sample core from the hollow core auger? Do people send in samples from a backhoe excavation for technical analysis? TMK