Using a demo hammer to drive posts

[scsmith42]

Has anybody ever done this? I have several hundred cedar posts to drive for a retaining wall on my farm. The posts average between 5 - 8" in diameter, and I need to drive them about 30" - 40" into the ground.. Using a slide hammer post driver on a tractor is very slow going.

I've got a Cat 420D backhoe and was thinking about welding up a socket assembly that would slide over the bit on a hammer and hold / position the post for driving. Near as I can figure out, a 1200lb hammer would be about the right size for my machine. I would probably rent the hammer, since I don't have much use for one otherwise, but if I could find a good deal I'd buy a used one.

All thoughts and advice is appreciated. Thanks. Scott

 

[PSDF350]

Probably cheaper and easier not to mention quicker to hire a post pounding company to come in. But if you must do it yourself anything is possible. Might also consider the wear and tear on your backhoe. If you do, do it dont forget pics.

 

[scsmith42]

PSDF350, thanks for the feedback.

Re using a post pounding company, the same thought had occured to me. All of the local folks use the slide hammer type of pounder that goes on a tractor and takes two people to operate. I had a couple of guys that worked three days pounding posts; only averaged about 40' linear feet per day (about 100 posts per day), and charged me $500.00 per day for the two men and equipment usage..

I've got about 600 linear feet of posts to drive, so this would work out to be 15 days, or $7,500 in labor.

I can rent a hydraulic ram for about $900.00 per week, and hire some day labor help for ten bucks an hour. If the ran is 1.5X faster than the slide hammer, I should be able to do it myself for $1,500 in rental and 800 or so in labor. At least, theoretically...

The comments made by you and others re wear and tear on my backhoe are one of my biggest concerns, if I go this route. Is it just the bucket pins that take a beating or will there be signficant wear on the entire hoe? I'm also wondering if the wear would be reduced since I'm pounding posts into dirt (that is somewhat soft) as opposed to breaking rock/concrete.

 

[DR RPM]

Doing the post pounding with your backhoe and breaker will work, similar to a sheet pile vibrator, just remember that only engage the hammer when you are on the post, as the hammers do not like to run free with no load. If you already use your machine with a breaker, this will be a heck of a lot easier on the pins and bushings than smashing concrete. Sometimes you just have to use what you have to do the job, we once used a Cat 988B wheel loader to push fence posts on my grampas farm, quickest fence we ever built.:bash

 

[digger242j]

I was told once, by an old excavator, of an attachment that he'd made for a 90 lb. jackhammer. It was a bracket that fit ove the top of his shoring planks, and when digging manholes and such, he'd set bracing in place and then use the hammer to drive the planks down into the dirt as he dug deeper. It seems like the same principle you're thinking about for driving your posts, except on a larger scale.

As far as wear and tear on the machine, I agree that it won't be nearly so bad driving wooden posts into dirt as what you'd get breaking rock or concrete.


Reminds me of a joke...

A farmer hires two guys to dig post holes for him. At the end of the day, they come back to the farmhouse and he asks them how many posts they got in. The first guy says he got 30 done. the second guy says he got 5 done. The farmer says, "How come he got 30 done, and you only got 5??" Second guy answers, "Because he cheated--he left them sticking up four feet out of the ground!" :bouncegri

 

[Wulf]

I'm no expert in this field but I wouldn't use a demolition/rock hammer to drive in posts.
When a hammer is driven against rock or concrete you always apply a bit of pressure on tool against the material before firing. The pressure applied and the hardness of the material causes the hammer impact to go into the material (breaking it hopefully) if there is insufficient pressure or the material breaks easily you can likely hear a metallic ping inside the breaker indicating blank firing.
When using it on a wooden post there will probably be insufficient resistance when firing and you will have the equivalent of a blank firing which can damage the hammer, worst case scenario is it could fail and contaminate your hydrauic system.

 

[digger242j]

Those are good points, Wulf and Dr RPM. It's certainly something to watch out for. I guess it would depend on operator finess and the resistance of the dirt to the post being driven. Personally, I imagine there would be enough resistance, but lacking any solid data one way or the other, I say we let SC Smith try it and report back to us. Better he should have to pay for the hammer repairs than us.

I'm no expert either, but I think the part of the hammer that might fail isn't going to be a part that's actually in contact with the fluid though.

Maybe somebody else knows for sure?

 

[PSDF350]

sc those guys must be slow, becuase several years ago my landlord/neighbor had about 6 acers fenced in for his fallow deer. The ground was tough (as in rocky) and it only took 2-3 days dont remember exactly. But I do remember the whole house shook when they where doing section right around us. If ground is soft why not just use a post hole digger?

 

[scsmith42]

All - thanks much for the feedback. To answer a few questions....

First, my backhoe is very tight ('02 model with 1700 hours) and although I'd like to save some bucks on my retaining wall, I don't want to do it at serious risk/damage to my hoe. I guess the question will be how much would the shock be reduced by pounding the posts into dirt, versus concrete work.

RE the speed of the manual slide hammer, it's taking the two fence guys about 5 minutes a post. When you consider that the posts are being driven on the edge of a pond embankment, and that they have to constantly reposition their farm tractor to line up perfectly on the post, and that it takes a couple of minutes to pound the post down to refusal, etc, the rate that they are achieving is realistic.

The backhoe mounted ram offers the advantage of not having to reposition the tractor with every post, and it should "vibrate" the posts into the ground much faster than the slide hammer. One option that bears considering is using a smaller hammer - the 1200 lb size is appropriate for my 420D, but apparently Bobcat's are able to use hammers to drive posts also and they have a much smaller hammer. This may reduce the wear and tear on my backhoe, albeit at a slightly slower pace. Does anybody have any experience with different capacity hammers on the same hoe, and if the wear on the machine is significantly reduced? Also, are there any types of rubber pin bushings, etc that might minimize the wear by absorbing some of the shock?

If you can picture a sloped hill that goes down to a pond, and at the edge of the pond water a retaining wall that is built from vertical posts that are butted up against one another, that's what I'm building. I had considered digging a trench and pushing the posts down into it, or filling the bottom with concrete and placing the posts into it, but the problem with the former is that the posts will be loose (remember that water is going to be soaking around the bottom of the dirt), and the problem with the concrete is that it will be difficult to replace posts as needed down the road.

Re potential hammer repairs, it will be a rented hammer, so I can dodge a bullet here!

I will be driving the posts into dense clay, so there will be a fair amount of resistance. I have heard tell of other fencing contractors (not local) who have installed posts in a similar fashion, thus I'm pretty sure that the concept is valid.

Please keep the feedback/ideas coming. Scott

 

[Bob Horrell]

Hercules Machinery Corp. in Fort Wayne, Indiana makes a wood vibratory pile driver that should fit your backhoe. It grips the post on the side like your hand would if you were to grab it (called sonic side grip). They aren't that hard on the pins of your hoe either. You could call them at 800-348-1890 and see if they have any in any rental yards near you. Good luck.

 

[scsmith42]

Bob, thanks for the info - I will definitely follow up with Hercules. Regards, Scott

 

[Dozerboy]

Don't worry about ware on your backhoe I have worked places that there hoes don't go anywhere with out a breaker. We even put a steel plate on them and use them for compaction in some cases, just don't run it with the extend-a-hoe ran out. Do worry about the breaker and it being damaged by not using it on concrete etc we have a breaker that’s sole purpose is to cut slopes yes I said slopes. Have you tried to just push them in the ground with the front or back bucket, sometimes I have had to have a load of dirt in the front bucket for weight. My only concern would be the post splitting or worse exploding with the breaker, which is why I would try just shoving them in the ground first.

 

[scsmith42]

Dozerboy - thanks for the info. Yes, I've tried pushing them into the ground -the posts shatter before going too deep. The clay soil on my farm is very, very dense; we had to sharpen the ends of the cedar posts to help them drive easier with the slide hammer.

 

[Bob Horrell]

Units like the Hercules use vibration and down pressure to put the posts in the ground. It is very easy on the post and the machine. They use this principle to drive large beams in the hardest of soils with excellent results. Usually it will drive right through rock (metal beams that is).

 

[Dozerboy]

I meant Don't worry about the breaker in my above post.

You could try soaking a few post and see if it soften them enough so they don't split. But it sound as if you may have to go with something like the Hercules setup to get them in. I have use the same type of deal to drive shoring in the ground sometimes you have to drive it in the ground has far as you can and pull it out fill the hole with water and drive it in again.

You could also get a 3"x5' schedule 40 pipe weld a cap or point on the end and a lifting eye or something on the other and use it to make a pilot hole.

 

[tuney443]

Why are you using cedar and not something harder with more longevity such as locust or don't they grow around you?Around here in NY,that's pretty standard for posts but you're doing this for a retaining wall so I might think you'd want steel--why not go to your scrap yard and torch the iron to a point and just drive them in with your hoe.

 

[scsmith42]

Locust is not commonly available near me. The cedar is being used for aesthetic reasons.