View Full Version : Fence Post Hole digging and ledge?
Jun. 29, 2012, 09:43 AM
Quick question here for the COTH world.
Have you ever needed to put a fence where there is ledge? If so, what were your options for drilling through and how much did it cost you per hole?
We're putting in 85 holes next week and at least 7 of them will need to be drilled as there is ledge near by.
I'm really interested to hear what others have done!
Thanks in advance.
Jun. 29, 2012, 12:41 PM
Ledge is tough to deal with. How much topsoil do you have? I have come to accept that I don't dig post holes down 3' at my farm! They go down as far as they can, and if they are too shallow, I use concrete to stabilize them.
I haven't ever investigated the cost of drilling through, but you'd have to have more than a regular post hole digger, I would think.
When I had my arena put in it was cheaper to raise the entire area to match the big rock than it would have been to blast the rock out.
Jun. 29, 2012, 12:57 PM
Be careful using concrete if you are using treated posts - they will rot very quickly. If you want to firm up the base of your post use crusher run gravel and tamp it down hard.
Jun. 29, 2012, 01:10 PM
Concrete or shift the fenceline - ie it won't be straight.
We have limestone close to the surface here as I discovered to my chagrin. The soils map said 30 inches but when you are on top of a ridge, it's right there.
We did have some power poles shifted and it took them two days to hydraulically dig and set three poles, so roughly an hour per foot in the worst case. I later contacted a local fencing pro and he quoted me $100 per hour for straight labor - he has a great reputation, he's fast and he's good so I figured for my three foot deep posts I was going to pay maybe $150 each. Or it could have been as bad as $300 each.
With T-posts on sale at $4 a pop I had to bow to my budget and not have the fence I really wanted.
Now, the power pole guys were using a specialty boom mounted hydraulic rig on a regular phone company utility truck, ie really big, that had a grinding tip auger and going down about 5 to 7 feet per pole. The fencing guy would have had a BelTec or Daneuser (sp) three point hydraulic unit also with a grinding tip on the auger.
We found a used BelTec for sale for $4500 at an equipment place and got there too late - it'd been bought the day they lowered the price, somebody else had been watching it too! Those units are only powered by the tractor hydraulics, although the tractor provides stability, they have their own feet and rams pushing the auger down or pulling it back up, or they can run backwards like a reversing drill and just corkscrew the dirt and rock chips to the surface. Tractor needs some horsepower to use it.
My neighbor had his pounded and I heard that he used concrete on the corners, his fence is NOT straight in some spots and he hasn't done the ridgetop at all yet.
Jun. 29, 2012, 01:30 PM
Interesting, thanks for sharing! (keep the stories and suggestions coming)
The fenceline cannot be moved. (small acreage, small paddock, fence going between ledge and driveway in front of the barn)
I'm planning on going down between 2 1/2 - 3 feet for the posts.
I'm using PT 4x4's.
When I was staking where the holes will be dug, at least 4 stakes went down 3" max, then hit ledge. Yup, that's 3 inches. :mad: The rest (81) went in like I could have driven them flush with the sledge hammer. So there's going to be at least 4 problem children, but I suspect more.
I have 10 yards of crushed gravel sitting in my driveway that we'll use to back fill the holes. Makes for more sturdy posts.
So, it is possible to drill the rock. That's good to know.
Cement is also a good idea that I hadn't thought of.
Jun. 29, 2012, 07:37 PM
This is unorthodox but can you build up on top of the ledge to give yourself the space? Might be too much area/fill materials needed, but if you only have 3" of soil, you are facing drilling the rock. Are you doing this yourself or having a professional fencing company do it?
If it's a professional company, you might just have to write a bigger check.
OR -consider posts that do not sink into the ground but are set into some sort of very heavy base that might be pinned down with smaller bolt type things? You'll have to cut off the tops.
The phrase Yankee Ingenuity probably came from dealing with our rocks. And winters.
Jul. 3, 2012, 10:48 PM
Well, we've only got two holes out of 80 that were ledge rock, so we're way better off than I suspected. I'm probably going to rent a pneumatic rock drill for those two, but the rest are set! Much relief felt there.
Thanks again for the suggestions guys! Lots of hard work left to do but at least now the posts are in! (well, all but the two...)
Jul. 3, 2012, 11:22 PM
When my husband and I would encounter rock ledges (than ran all through some of our fields), we would did as far as we could go (we were using locust posts), then he would hand drill the rock with a chisel. He would then take a 1/2" metal spike, drill the end of the post and hammer the spike into the bottom of the post. We then set the spike into the drilled hole to help stabilize the post and then pour concrete around the post. Most all of them are still up/original posts and we put them in in l998. Very hard work though.
Jul. 3, 2012, 11:56 PM
A layer of gravel at the bottom of the hole helps drain the mositure away
that the concrete would hold.
We have 10-12 inches of clay, then a thick limestone layer. We have some of it fenced with pipe corners/braces that the installers drove in with something rigged to their tractor. Some posts took 2 minutes, the others
up to 20 plus minutes. Had to set the t-posts (used the full covers on them)
only as far as the ledge so stuck a pipe post every six of seven for stability.
The next time we replaced a stretch we did all pipe posts pounded 4 feet in.
The line with wood posts we attempted 5 or 6 years ago....what a fiasco.
the rock driller we rented just bounced off the limestone. Found a guy that did the utility posts and he had his hands full...his rig rocked and rolled. His minimum charge was $250 and we needed about 15 holes done. Between
the rental for the so-called rock bit thingie and his fee, it came to $26.33
a hole. Sigh! But it was well worth it....we would still be out there trying to
do it ourselves.