OT: Post Pounding and Damage

[SteveF]

Ok, have a fence guy coming out and to put in the 5" fence posts he is going to not drill holes and insert but use his fancy post pounding machine. No problem with that except that he will pass about 20' from the foundation of my garage. The block foundation is dug into the hill so I really don't want it cracked.

Understand that post/piling driving and building damage is established science. There are small engineering companies that earn their living by calculating and monitoring construction vibrations so buildings don't get damaged.

I know of one case in central Ohio where a coworker had a big truck drive down the street about 100' from his house and periodically stop and slam a big weight into the ground to set up ground vibrations that could be measured by a company searching for oil. Shortly thereafter he and several others on their street found cracking in their basement foundations. Left that contract soon after so don't know how his discussions with the survey company went.

So, any anecdotal stories of bad things that have happened with a fence post driving project. I'll even take one where it was the father of your cousin's girlfriend that lives on the other side of the country.

Steve

[sid pileski]

I'd say if you worried, and I might be too, see if you can drill those few that are close to the foundation.
Better safe than sorry. They probably have done similar situations a thousand times, but you'll sleep better at night.

Sid

[Black Forest]

Find out if his machine is a press type or a hammer type.

[QSIMDO]

How thick are the posts and how deep?

We had a 3 point hitch hydraulic driver for driving in guard rail I beams...scariest damn thing to work but the effect was extremely localized.

[CCWKen]

A lot depends on the type of soil and moisture there in. My soil is like concrete when dry but after a rain, I could nearly drive a 5" post with a framing hammer. I have to keep the tractors out of the fields for nearly a week after a rain. Some field drainage spots even longer. The JD crawler comes in handy for pulling tractors out of the muck but takes two drivers that I don't often have. So I stay out of the fields.

If the foundation was properly backfilled, you shouldn't have a problem. The soil should be somewhere on the damp side but not wet. If you're worried about it, park a couple of cars between the foundation and fence line. That will help absorb/dampen vibrations.

[GNM109]

About 6 years ago, I decided to remove the old rustic cedar fence around the front of my place (2 acres, rural). The white vinyl fences had come into vogue and we rather fancied having one. I found a licensed contractor and hired him. He came out equipped with a tractor that had a 12" diameter hydraulic auger post hole digger.

The contractor and a crew of two men did the 50 or so post holes needed for the front acre. They were all nicely concreted and the rails installed in less then 6 hours, start to finish.

I don't like the idea of pounding post rails either. In fact, it would be tough in my area since about 2 feet down we have a layer of hard pan clay that is almost as tough as concrete.

I would simply find another fence contractor, one with an hydraulic post hole auger.

[SteveF]

A lot depends on the type of soil and moisture there in. .......................

That's just the start. Found a couple of nice documents on pressure wave legal limits and calculations, unfortunately I have no way to measure any of the dozen or so variables except for distance to the structure to be able to make those calculations.

Yeah, I've considered drilling the ones near the foundation just to be safe. Probably not necessary but it just sucks to learn lessons the hard way. Especially when it's cases of "Mo&$%*#$&er, I was afraid that would happen".

5" round posts going 24" or so deep. I suppose I could water the soil a few days before to help the process.

Steve

[Willy]

[QUOTE=SteveF;1097526
.........................
Understand that post/piling driving and building damage is established science. There are small engineering companies that earn their living by calculating and monitoring construction vibrations so buildings don't get damaged.

..................

Steve[/QUOTE]

I believe a lot of the possibility of damage is based on the make up of the soil/rock conditions at your site. Soft loose soil won't transmit vibrations nearly as far or intensely as clay, never mind rock.
One would almost need the resources of a geotechnical engineer in order to accurately ascertain with any certainty whether there is going to be damage inflicted to your foundation. Anything else is only speculation.

Having said that I know several folks that have used tractor based hydraulic post pounders for years and have never heard of any incidents.
But if in doubt use an auger type or get out there and dig them by hand, not fun, I know.

[Normanv]

I have driven many posts into heavy clay soil using a hand post driver. I do not understand what you are worrying about, the impact(ha!) on the surrounding area was of no consequence. Even the worms did not come up to see what the fuss was about.

[brian Rupnow]

I once seen a demonstration of pounding a fence post into dry soil with a compactor held on the end of an excavator boom. About 12" in the post hit a rock and split. the part that split off flew and hit a woman watching the demonstration in the head. She ended up in hospital with a concussion. Us "watchers" could feel the ground shaking 60 foot away from the post. I wouldn't have it done anywhere close to my foundation.---Brian

[Normanv]

Brian, we must have different soil conditions on the Isle of Wight and Canada.

[lakeside53]

20 feet way going down 2 feet... pretty much a non-issue. I wouldn't have a problem with it.

[RichR]

I would simply find another fence contractor, one with an hydraulic post hole auger.

This^. Consider the possible aggravation and extra expense this guy with his "fancy post pounding machine" could inflict. Once they've
caused damage, it becomes your problem to repair, prove it was their fault, take them to court, etc. Take the safe route.

[Mike Amick]

I think your thought of watering down the ground before hand is a good one.

And I would find out the answer to Black Forest question on if it's a hammer or a press deal, if it IS a
press process then your worry is definitely unnecessary.

But .. I agree with some of the others, 20ft is plenty of cushion either way.

[Normanv]

Going back to the original question, the dropping of a huge weight on the ground and knocking in a puny post does not compare. I think that you are making a mountain out of a molehill.