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Power hammer foundation follow-along


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Sorry to change the subject again but make sure you keep us posted on that little baby on the way! 
 

my wife was 24 hrs in labor with our son, it was a long haul at the hospital but even after all the pain and stress she was glowing when she held our boy! 
 
I never understood the term glowing till I seen it first hand! 
 

I will say that the hospital food was terrible in my opinion lol, after eating that stuff for three days I was glad to get outta there! 
 

mom will need lots of sleep when she first gets home the next day or maybe two,

I found pushing the baby around the house In the bassinet worked perfect to put him to sleep, that and I download 12 variations of “ah vous dirai je maman” by Mozart the cover artist I got was called John Novacek, it worked like a charm lol! 

 

 

 

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On 9/28/2021 at 4:02 AM, TWISTEDWILLOW said:

make sure you keep us posted on that little baby on the way!

I sure will! Some posts back I said the baby would come in two weeks. I don't know what I meant then! The baby is supposed to come on the 6th of November! So 3,5 weeks! :blink::D It seems to me my partner is glowing already when she's talking about the baby. She is so happy! :D

The workshop has to wait because I sold some timber and I have to do pre-harvest clearing over the coming weekends. But on the other hand it might start moving faster during the weeks because I decided against using threaded rods, pipes, and nuts welded onto plates. It is way too overengineered for a hobby shop. I would spend a lot of time sourcing all the different parts, thick steel, pipes, weld nuts that might warp, then weld it all together with a few millimeters' tolerance. Instead I will drill holes and use Hilti's chemical anchoring. This means I can start digging soon, get the foundation cast and then I can move on to the floor.

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Congratulations on your impending fatherhood.  Is this your first?  If so, it will change your life in ways you cannot imagine.

My late wife and I were not trying to start a family but we were being a little casual about NOT starting a family and we had to swallow hard when the little test strip turned color.  That said, I am REALLY glad to be a dad.  My son is 30 now and even though there have been some rough times fatherhood is something I am very glad I have experienced and it has made me a better man.

Good luck.  You are starting on a long and strange journey.

GNM

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Dad and I dug a pit for the foundation during the weekend. Yeah, it's an oversized dig-out but that can be filled in again. What's worse is that the deeper we dug the wetter it became. Mud, silt and dead organic matter. Dad called it soap mud. We live on an old sea bottom that was revealed due to tectonic uplift. We managed to push an iron rod 2 meters down into the mud using our hands, easily. What you see on the pictures is when we tried pushing a 3 meter pipe down. It went down 2 meters and wouldn't go any further. We have bedrock sticking up out of the ground 10 meters away, so it might well be bedrock 2 meters under the pit floor.

We had a professional pole driver on site for assessment. He said he can't drive poles there because his machine is on the back of a tractor and with the pit there he can't get in place. But he encouraged us to try pushing down steel rods on our own as its such soft mud, like hydraulic piston rods, using our tractor.  He said the walls in any pipes we push down only need to be like 6 mm thick. I could also hire someone else with a small excavator to drive down poles. He said a pipe, I think it was with a 90 mm outward diameter, can is rated for 20 metric tons.

So the plan is I will drive down 5 poles of some kind on my own, position them on the 4 corners of the block and one in the middle, and weld them to the rebar cage. Perhaps put small plates on top of the poles. The bottom ends should be welded shut and preferably slight convex. I will fill the hole until the bottom is good and even and cut off the pipes at like 4 inches. This is really fun! :D It's fun to push one's boundaries.

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Do you get earth quakes where you live? 

What is the depth to refusal (where the pipe stopped) from the surface? 

You have more issues than simple support under the hammer. The soil conditions are past the liquid limit, meaning it will flow like a liquid if you shake it. Your power hammer is going to shake the dickens out of it and 4-5 vertical small dia. pipes won't keep it from shifting sideways. 

If possible muck it out completely, make a caisson like John suggests if necessary. Then you can back fill with good fill. You'll want large rock on the bottom so water can flow through the foundation, then a compactable fill but still coarse so water can flow and lastly a soil gradation that will compact hard. You'll need to line the excavation with a geo textile before you start filling so the fines (mud) won't infiltrate the fill and prevent the free flow of water. Not trapping water under a foundation is REALLY important.

A rating of 20t for 90mm pipe is NOT going to apply in your situation. That is only for a straight push and your real concern is lateral movement and there's nothing between your poured concrete and bedrock but liquid mud. Balance a 4x4 on end and you can put a few tons on it easy but stand next to it and you can push it over with one finger. Make sense?

There's no point in capping the piles (pipe) they aren't going to displace enough to provide support that way. A capped bottom end makes a displacement pile and you're not going to get ANY support from displacement the soil is liquid and free to move with virtually zero resistance. You pushed it to bedrock by hand. Yes?

Leaving the ends open will provide sharpish ends more likely to catch on the bedrock and not skid. If it's as soft as I think it is stuff the ends with rags so water and mud doesn't flow into the piles freely, I'll explain in a bit.

I strongly suggest you angle the corner piles outwards as you drive them. More of an angle than a kitchen stool but no more than a camera tripod. Then drive two vertical piles under the center of your foundation, the hammer location. The angled piles are known as "batter piles". Connect all of them with welded rebar in two levels. One close to but not in the water, the other below the proposed finished surface of the foundation. 10-15 cm. Don't weld it in a straight box, connect them crossways too corner to corner include the center piles of course. Once it's secure enough start dropping good sized rocks in the mud, shove them down as far as you can. Don't just dump a loader bucket full in, place them a few at a time so they'll displace as much of the mud as possible. Muck the mud out as you go.

As crazy as it sounds in the conditions you describe the steel piles need to be strong and rigid enough to stand in the yard with your power hammer running on top of them. 

Once you have the fill emplaced and compacted it's time to pour the concrete cap. First drive a piece of rebar down each pile till it stops, leaving some sticking out. Hopefully the concrete will flow into the casing, displacing what water has seeped in. Pour your concrete cap and finish it. Once it's cured it's going to be as good as it gets without going to real extremes.

I spent 20 years working for the foundations, Geology section of the state dept. of transportation. I didn't design foundations I collected data in the field so the engineers could. You can't spend 20 years and not pick up a trick or 100. Everything I described is similar to  bridge foundation in similar soils conditions. We have bridges on floating foundations held in place by batter piles.

The above is a general run down, if I have more information I can make more specific recommendations.

Frosty The Lucky.

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Also, when you pushed the pipe down did it stop as if it was hitting rock or was it a "soft" stop?  It is possible that you were hitting a dense clay layer rather than rock?

Listen to what Frosty says.  He has got a LOT of experience in this area.

"By hammer and hand all arts do stand."

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It could be an erratic, sure. A person could use lengths of rebar as probe rods, angling out from the proposed foundation and look for an edge. If it were large enough it should be pretty stable itself.

How would you cast concrete under 2m of muddy water? The two methods that come to mind would be to case (caisson) the hole pump it out and cast the foundation as a monolithic pour. With the attendant problems.

The other thought would be to build a support structure and pour the foundation in lifts lowering it into the hole as you go to displace the mud. When it wants to stall a simple water jet would clear the compressed mud so the block could settle. 

Were the ground clear I'd want to bring a drill in, drill the casing into the bedrock a foot or so, tricone a couple sockets in the bedrock inside the casing to drop rebar in and tremmy the casing with grout. Lastly cast the foundation block on / around the casing.

Tremmy means the grout is pumped to the bottom of the hole, casing, etc. filling it from the bottom up. This displaces problems like water, mud, organics, etc. as the good stuff is forced in. We decommissioned some drill holes by tremmying bentonite to seal penetrated formations. Rare but we did it occasionally. 

Frosty The Lucky.

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11 hours ago, Frosty said:

Do you get earth quakes where you live? 

What is the depth to refusal (where the pipe stopped) from the surface?

Thanks for the information and suggestions. I'll answer a few of your points now and come back later and re-read it and think about it.

We have no earth quakes. So little in fact that Finland has dug nuclear waste disposal sites 420 meters down at Onkalo.

The depth to refusal is about 1.5 ━ 2 meters from the bottom of the drained pit which is also about the same as the bottom of the planned foundation. When pushing the pipe down it lifted the wheels on the Valtra 8400 (5 ton tractor) until the flatness in the tires went away, then the pipe bent. So if it is bedrock or not is anyone's guess. Bedrock comes up out of the ground 10 meters away, 30 meters away and again 30 meters away.

The piledriver professional said we should weld slightly convex caps on the pipes. He said the edges should still be sharp so they grab the bedrock. You mention displacement piles, and that the mud is too soft for it to matter. But perhaps a cap would stop the pipe from buckling in the bottom end?

You also mean we should fill the pipes with concrete? Is that perhaps overdoing it? How large a pipe diameter would you recommend? How about using open profiles like U-beams, with some welded supports to prevent buckling, or small I-beams? It would be cheaper to raid the trash pile. I made a sketch, is this how you meant it?

Check out a video of pushing a rod down at my instagram @jarntagforge
https://www.instagram.com/p/CVYgVLmsVXU/

Piling.png

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I made a more realistic sketch after thinking about it a little more. I guess I had nothing better to do than to draw this in paint. I even have AutoCAD and a 3D-modelling software. I asked about using for example U-profiles. I am a mechanical engineer now so I guess I know the answer. They buckle easier than pipes. Supports welded on regular intervals on U-profiles make them stiffer, welding all the way makes them a pipe in the end. Pipes are better.

 

Piling2.png

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Does anyone know how to go about welding the lower level, if it's still wet then. I looked up welding in wet conditions on Google and every single page say it can be done but that it's life threatening. I know the current should want to go the shortest way so I should put the ground right next to the place where I weld. But I'm unsure of what makes it dangerous. Forgetting the ground is all I can think of?

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The video clip says it all about your soil's ability to support your power hammer. If you lowered it into the pit it'd sink until it reached a supporting lens or compressed enough much against the solid lens to support the weight. To give an indicator of it's nature, bedrock or dense soil, push the rebar as you did in the video till it stops then hit it on the end with a hammer. If it advances then chances are it's stopped on a layer of dense soil. If it bounces then chances are it's on bedrock at THAT location. It COULD be a boulder. Repeat this test at different places in the pit if the rod bounces at all or most locations it is or can be treated as "bedrock" for the purposes of your foundation. 

If that isn't clear, let me know I'll clarify.

The sketch is pretty close to what I think your minimum foundation requires regarding piles. Is the space between the piles filled with rock and gravel? 

I'm not clear, is the wire frame drawing at the top of the piles a rebar frame or something else?  Do NOT cap the tops of the piles, if you're lucky concrete will fill them, making them more rigid and less likely to bend in use. I do NOT see a pile directly under the hammer's anvil. That is THE point that WILL take the most abuse from the hammer and as drawn all the support it has is the concrete cap between piles. 

I can't imagine bending or crumpling 100mm steel pipe advancing it to that bearing layer. Of COURSE the pile driving service refused this project, One bounce with a pile driver would crush 100mm pipe. There is ZERO resistance to the casing advancing to the bearing layer, it'd be like hitting a nail with a hammer to get it to the bottom of a bowl of soup. Tomato soup.

Structural steel other than pipe will work well if it's the right kind. U channel would work if you doubled it back to back welding it into an I. Wide flange / H beam is a common shape for pilings and would work well for you. You shouldn't need more than a sledge hammer to advance them the last few inches. 

I'm not joking when I say you need to build this foundation like it was standing in open air, the soil there is like pudding. (A technical term we used to describe soil like this on the drill crew, it even showed up in foundation reports and recommendations.)

Thomas made a suggestion about sinking a rebar grid to the bearing layer and building on it. I think I misunderstood just what he meant but thinking about it last night I realized a version would work well in this situation. Build a rebar grid to match the pit's size and shape then build the pile structure on it. This would let you weld angle reinforcing from top to bottom and boxing the entire structure. THEN lower it into the pit and GENTLY press it to the bottom with your tractor bucket. If you have access to a concrete vibrator you could advance it to bearing by vibrating it. Remember to put a pile under the power hammer's anvil.

Whatever you do for piles you REALLY need to backfill with rock and gravel to keep the piles from walking when the hammer is working.

Frosty The Lucky.

 

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1 hour ago, Frosty said:

Build a rebar grid to match the pit's size and shape then build the pile structure on it. This would let you weld angle reinforcing from top to bottom and boxing the entire structure.

This would also eliminate the need to weld on any steel that's already been sunk into the pudding.

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1 hour ago, Frosty said:

is the wire frame drawing at the top of the piles a rebar frame or something else?

I sketched what you said. Rebar cross-linked at two levels. If you mean inside the concrete foundation then that is also rebar. Some sturdier rebar at the bottom. At the sides and higher up just 6mm/200mm reinforcing mesh.

1 hour ago, Frosty said:

I do NOT see a pile directly under the hammer's anvil.

Good point. There should be two piles there instead. Ignore 

1 hour ago, Frosty said:

Thomas made a suggestion about sinking a rebar grid to the bearing layer and building on it. I think I misunderstood just what he meant but thinking about it last night I realized a version would work well in this situation. Build a rebar grid to match the pit's size and shape then build the pile structure on it. This would let you weld angle reinforcing from top to bottom and boxing the entire structure.

So this would include piledriving? When you say structure, you mean the full previous plan? Thomas also talked about "casting around it". I don't know what that is about.

I made a drawing. The cage could keep the piles from wandering out, but the piles would need to be driven last and then welded only at the top. You said angle reinforcing, is that for the cage or the piles? Because the piles need to bottom out at unknown depths and so can't be welded at the bottom. If you would clarify all of this then that would be great.

 

Piling3.png

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I sent my last post right after you sent yours so we can ignore the weirdnesses.

Your seen from above "plan" view is what I was describing. Yes.

The structure that will support your hammer is the piles, the welded rebar ties it together so it won't wobble and reinforces the concrete at the top. A cage as drawn won't have much effect unless it's cast in the concrete. If you filled it with rocks and gravel there's a chance it'd split a seam (blow out) and the fill would migrate out from under the hammer. 

If you were to build the rebar grid with welded on piles and cross bracing then sink it in the pit there would be NO "driving." That soil doesn't have any end bearing resistance, you could slowly push it down with the bucket on your tractor or vibrate it down. The soil you have is so soft you won't have to "drive" anything, push it maybe.

You'd need to build a caisson, muck and dewater it to "cast" concrete around a rebar mesh footer. I don't think that'd be very practical I wouldn't do it. Thinking about it just now, a person might be able to pump grout to the bottom of the pit and sort of poop a layer on the bedrock over a rebar grid and around the piles. I don't know who does that kind of work, even here.  

This is leading to more ideas, the voices are chattering! Another thought would be to make a cap for the pipe piles and pump grout down them to poop out a bedrock fitting foot on each pile. Flush the bedrock with water first for a clean contact. Hmmm. The two piles in the center could have a largish opening in facing sides, drop a piece or two of rebar down the sides and the grout would pump out, connect and you'd have a concrete footing. 

I'm getting carried away here, I'll let off the ideas. Quiet voices, QUIET I SAY!:)

The more you can fill the pit around the piles with rocks and gravel the better but you're getting the idea.

Frosty The Lucky.

 

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17 minutes ago, Frosty said:

The structure that will support your hammer is the piles, the welded rebar ties it together so it won't wobble and reinforces the concrete at the top.

So the last picture minus the rocks is what could work? A welded rebar cage is first pushed (driven!) down in the mud until it hits the floor. Then piles are also pushed down inside the cage but still not connected to it. The cage is cut off some distance below where the footing will be cast. The piles are welded together at the top at two levels. The uppermost level is cast into the concrete footing. Do the piles have to be at an angle still?

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I would NOT use a "cage", I don't know what it's supposed to do.

Push all the piles until they stop, give them a couple taps with a sledge to make sure. Your most recent drawings show piles stopping BEFORE they reach a bearing layer. That would cause your hammer to tip as they sank to the bearing layer. 

Keep it simple. Drive your pilings, weld rebar or stronger to connect the tops. Then start filling around the piles and in the center with rocks and finally compactable gravel. Once you have the pit back filled and compacted weld up the rebar to reinforce the concrete cap under the hammer. 

Piling rock INSIDE the piles won't prevent them from splaying outwards under the hammers tender mercies. Embedding the pilings in rock and gravel should lock it all in position as well as is reasonable. UNLESS you want to muck it all out and go to extremes.

Frosty The Lucky.

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