concrete for a 250 little giant

[hillsideshortleg]

I am starting to think about poring concrete for my 250 little giant footing. The area of the shop I want to put it is on has around 10' deep of fill. The fill is a clay mix. Is this a mistake. Any advice? I see the size that is recomended for this hammer and was thinking I should increase the size, but then I am also thinking I may be stepping into my next pile of crap. But I have been trying to keep my feet clean
Thanks
Rick

[Bentiron1946]

How deep is your fill? If you can reach undisturbed soil you will be better off than setting it on an unquantified back fill in my opinion. When a big hammer gets to pounding it will quickly settle your back fill so I think you will be stepping in to a pile of crap big time. I have seen the recommended drawings for a 1,000#LG and they had RR ties in the bottom and then concrete on top of them. So maybe you could excavate down to undisturbed soil and put in some 8' RR ties buried in 4' and then put in concrete up to floor level. Of course we don't have any idea as to what native soil is but it surely is better than unconsolidated back fill.

[Yetti]

well for what I know about machine bases if the footing has been filled or disturbed it will need compacted. problem 1 is depth. you need to compact in layers. if not then you may need to drill holes and put in piles for the footing. piles will stabilize the floor and prevent it cracking and shifting. I would do some research about the requirements of the machine.
My shop is 7"-8" average depth. it will support a good amount of weigh given that it has a rewire rolled into it and its bedded on a 6" of gravel under that. I would think the machine would require at least a bag mix if not as high as a nine bag(very strong). its just a thought, but if you called a concrete company they may have an engineer on hand to figure out what you need.

[peacock]

How long has the 10 ft. of fill been in place? If it is fairly recent you may want to rethink this. You could make a temp. base out of timber. A 250 is heavy and much taller than the base is wide . If it would settle straight down not so bad but if it starts leaning could be serious.

[Frosty]

10' of clay isn't a good thing, especially if you have a high ground water table, if it's wet it'll liquify, "see liquifaction." If on the other hand it's dry it'll act much like concrete.

It's a tough question without having some specific info but as a general rule of thumb. Excavate to undisturbed soils and examine the aggregate. If it's wet fines it's going to need work, maybe lots. If it's well drained gravels or what's known as NFS (Non-Frost- Susceptible) and compacted in situ you can work your way up from there. Fill using a properly graded aggregate in lifts and compact to "limit" (This would be as much compaction as it's reasonably possible to achieve. I'm pretty sure "limit" is the wrong term, it's been decades since I worked in the soil's lab.) fill in lifts of 2' or less and compact with a "jumping jack" compactor till it bounces without imprinting the foot. When you get to the final 2' before your foundation horizon fill with D-1 and compact first with the jumping jack and finish with a plate compactor. Avoid using much water compacting, just a little. If free moisture appears around the compactor's foot or in the compacted trail you're using too much and it'll lower the final soil's density.

Call a local soil's lab or the local highways soil's lab with your location, street/road and address. They'll have the most recent test results from the road grade and seeing as it's a public office they'll share though you may have to go to the office and make copies.

Wish we lived closer, I'd come by and show you some field tests.

Frosty The Lucky.

[jason0012]

I remember how Clifton's 250 leaned from subsidance under the foundation. If you watch the videos you can see the hammer leans forwards. He said the problem was the wet conditions, and quantity of sand in the soil. His hammer sat right at the edge of the foundation and all force was on the front edge. As I recall he said that the foundation should have extended two feet or more in front of the machine to stabilize it.

[hillsideshortleg]

The fill is around 5 years old. In that corner of the building I pored a peer on virgin ground then used barrels welded together to get the height I needed and tied it all together with rebar. Yes I stepped into it back then and now I am thinking anything I do on that end of the building could create settling. I am going to have to rethink my whole shop layout. Thanks for the input. I did compact it in lifts with the wheel of my tractor(but I dont think that counts) 5 years ago I ended up getting 50 to 75 loads of fill in a 3 day period. I was pushing dirt so fast I could hardly keep up.
Thanks again

[Bentiron1946]

I be a bit on the conservative side as far as just digging a pit and dumping some concrete and rebar in. I think you need to go down to native soil and like some one said recompact that soil up to you current grade and then put in some decent piers with a rebar cage to support the hammer pad. Another way to do it would be to get some Burke tube and put the rebar cage in that, then the concrete, then back fill around the tubes, pour your hammer pad and then put in a new shop floor around that. There is no way to short cut this job on a big hammer. If you try to short cut it you'll just wreak havoc on the rest of you shop structure, shake, rattle and roll and it all may come down when you get a 250# hammer forging away in a jury built structure.

[Frosty]

Hey Bentiron, this may be a bit off topic but do you need to borrow a snow shovel or plow truck?

Back to the topic, there is a foundation design for virtually any soil conditions, you may be surprised at how many bridges in Alaska are on floating abutments, only stabilized with piles and batters.

You are right, rolling fill down with a tractor doesn't count unless you're leveling a pasture. You CAN get away with using a backhoe bucket like a hammer and beating it down but you'll still need to do the final fill (sub base) with a proper compactor.

My 50# LG sits on my slab without special foundations, the slab is reinforced in the area with double rebar and a small downward facing curb to prevent it drifting under vibration. The soils are glacial till and drain reasonably well, the fill is 2' of D1, yeah, the guy who owns the pit is a friend and neighbor I used to drive for occasionally before the accident.

A 50# LG does not require anything special so long as the subsoils are properly prepared and have no serious issues like high groundwater. Sand is NOT particularly good unless it's crushed, even then.

For your or anyone's personal design I recommend talking to the local gvt soils lab or road and foundations design department. This is what they do for a living and like most of us if you show interest in what they do they're usually pretty receptive to helping out. Just don't expect them to put themselves in a position of liability without a proper work order.

Frosty The Lucky

[hillsideshortleg]

Heck I may as well dig out a basement and put in there. A light bulb minute!!!!!

[peacock]

When we installed Tom Clarks 250 it wound up being easier to pour a base outside the shop door install the hammer there and build a roof over it. These kind of issues are why big hammers sometimes sell for less money than smaller ones. I know of a guy that bought a 300# Chambersbrug and didn't have enough electrial service to run it very disappointing. It's kind of like pipe diameter, double the sze quardruple the cost.

[pkrankow]

How about put some piers down to good earth, then pour a slab on the top of the piers. Put a layer of isolation material then pour the thick reinforced slab on that. 28 days of curing later put the hammer to use. You can use a power auger to drill the pier holes for concrete, or hydraulically ram pipe if you know about how deep the bedrock is (if there is bedrock within reach).

Phil

[781]

The original plans that came with my 250 Murray hammer stated the foundation should be 4' wide 5' long and 3' deep which is what I did. This set up was for industy where the hammer was to be used every day and your shop may be different.

My 60 kilo air hammer from Tom Clark just sets on oak boards the size of the hammers foot print and this just sits on an old concrete floor and I havent had a problem other than tipping it over once when rolling it back into the shop after loaning it to a local group for their conference.

[iron quake]

I’m on the same type of clay / decomposed granite fill that you are on. We used a fantastic concrete contractor in the Spokane / Coeur D Alene area who poured a bunch of concrete for our house, 9’ basement walls on 3 foot wide footings plus all the slabs in and outside. He has been pouring in the area for 30 years. He knows our soils and climate and told me this about your situation. Clay settles back to compaction in most circumstances in 5-7 years. That being said, to be sure your hammer stays in place he suggested auguring down to native and pouring 3 pillars with lots of bar in a seven sack or better mix and then pouring the big chunk on top of that You won’t need any sona tubes if the clay doesn’t cave in and stays in place. How you get a 10 foot auger inside your shop is an issue perhaps. Peacocks idea might be better.
In setting my 100# LG hammer I removed the fill and got down to native soil which happened to be at about the 24” and took the concrete down to 36” I flared the bottom of the hole and then welded up a cage from 5/8” rebar. I’m very happy I put in the extra effort because the hammer would have been through my 5” shop floor by now. A couple things to consider that I think made mine work out well. Raise the hammer up a 6” or a 2 x 6 width perhaps that is not needed for a 250 I don’t know. Put 45’s on the front corners so you can get a tread bar extension down to the floor easily. Make a steel template to locate the ties rods and use that to position them by welding them to the cage. Put a PVC sleeve around the upper 6” of tie rod so you have some play if you need it. I put caps on 1 ½ PVC and then put a threaded hole in it to match the rod size and then it was easy to screw them up and down to the correct height for the final pour. My former boss and mentor told me “Do the very best job you can and it will be bad enough then” applies in this instance for sure I think.

[Sask Mark]

If the clay is a plastic type, it will expand and contract with the hydration levels causing the soil to heave and settle regardless of how long it has been in the hole or how well compacted it is..

Personally I would have 12 to 16" diameter concrete caissons put in that would be bearing on/in the till. This can be done with a low overhead drill rig or skid steer with a drill. You can even excavate holes for piles with a hydo-vac truck.

I would use Sulphate resistant concrete for the piles. I would use rebar cages with 4 vertical bars of 3/8" bar and tied with rings of 3/8" bar at 1' spacing.
For the slab I would pour it on 4" void form. I would personally pour about a 2'+ thick slab for a big hammer like that and embed the anchor bolts into the slab. The slab would be isolated from the rest of the slab with 1/2" apshalt impregnated fiberboard. Iron Quake suggests many similar ideas that sound to me like they would work.

The other alternative I would consider would be to excavate out all the fill and place granular back in the hole, placed in 6" lifts and compacted to 95%+ proctor density. I think the pile option would be quicker and cheaper.