Crawlspace Over Helical Piles - The Detail 1

[KootK]

I've never done this particular combo before. It's in WY and high seismic for what that's worth.

I worry a bit about tolerances. When this setup is spread footing, one can easily accommodate some misalignment between the wood post and the footing. For helical piles, however, I feel like the wood post pretty much has to land within the perimeter of the screw pile cross section. The alternative would seem to be grade beams in both directions which would raise some eyebrows.

Questions:

1) What do you dislike about this setup?

2) Got any better ideas?

 

[XR250]

I usually forgo the cap and post and support the beam directly on the helical shaft with a brackety thing. Fairly common around here. They are pretty good about lining things up.
Is this just the interior or the perimeter as well?

 

[dauwerda]

Don't you need grade beams (or something similar) if it's high seismic anyway? That whole seismic tie requirement (1810.3.13 of the IBC)

 

[WARose]

1) What do you dislike about this setup?

In my neck of the woods, for a crawlspace, the "post" would some CMU. But maybe this would be better.

Also, as another poster said: do you really need the cap? Most of those guys give you some hardware to attach to.

 

[KootK]

Most of those guys give you some hardware to attach to.

Does that mean that you see that connector as something supplied by the helical pile supplier?

 

[XR250]

The local foundation contractors (around here) will fabricate a bracket - typically something made out of angle

 

[WARose]

Does that mean that you see that connector as something supplied by the helical pile supplier?

Not necessarily. It just depends. Recently (for example) I had to connect to something like that. They provided the base (with bolt holes) and I bolted my base plate to it. (It was a small steel column.)

 

[phamENG]

10" dia. helical pile? Is that the diameter of the shaft or of the disk? I'm used to seeing a 10" disk, but a 10" shaft? That some serious load capacity - or soils with a void to solids ratio of approximately 1:0.

If it's a 10" disk with a little 2" shaft (which is what I'm accustomed to), then I really don't like your detail. You have a pin on top of a pin on top of a pin.

In similar circumstances (no seismic, though), I've had helicals with a grade beam on top and masonry piers with wood girders, etc. above that.

I think I agree with the suggestions to delete everything between the pile and the girder and just have a bracket there. You may need to case some sort of collars around the pile and anchor some sort of bracing, depending on the size of the pile shaft.

 

[KootK]

Is that the diameter of the shaft or of the disk?

The disk.

You have a pin on top of a pin on top of a pin.

Yes, to the extent that's true, that is very much one of the concerns. What's the solution though? Grade beams in two directions?

 

[phamENG]

Grade beam in one direction, assuming you meet the IRC levels above grade requirement for ignoring instability in the other direction. If you don't, then either grade beams in both directions or spread them further apart and put in P-2's. If you do meet the IRC exception, you could stagger your piles along that pier line to to provide some nominal torsional support along the grade beam to make yourself feel a little better. If this is interior only, I'm not all that concerned about the pinned wood post - you'll have a floor diaphragm, etc. to stabilize everything up there.

 

[jayrod12]

Count another vote for extend teh helical pile to underside of beam. But make sure your lateral system (I am aware who I'm talking to) isn't relying on these piles. I've found the lateral stiffness of them is not overly signficant, despite what the manufacturer will tell you.

 

[KootK]

...assuming you meet the IRC levels above grade requirement for ignoring instability in the other direction.

Can you tell me a little more about that such that I might located it for myself? Is it the bit shown below?

If you don't, then either grade beams in both directions or spread them further apart and put in P-2's.

What are these P-2's of which you speak? Pairs?

If you do meet the IRC exception, you could stagger your piles along that pier line to to provide some nominal torsional support along the grade beam to make yourself feel a little better.

I'm kinda starting to feel as though my interior condition might be better off with a stem wall so that at least I can lay claim to a wall within whose thickness the pile falls.

Is there a provision that deals with the stability of isolated piles without triggering grade beams each way?

 

[KootK]

Count another vote for extend teh helical pile to underside of beam. But make sure your lateral system (I am aware who I'm talking to) isn't relying on these piles.

Thanks for the gentle nod to my lateral chops. All my hardline stances go out the window, of course, when it's my project.

The interior condition is not part of the ostensible lateral system, other than hold down for shear boundary elements in a few spots.

The exterior condition piles were intended to be the lateral system. The only other story that I can think to tell with this is a loosey goosey tale about grade beam friction against the adjacent soil and some direct bearing into the soil at the corners. Granted, that probably is the reality of it. In this sense I don't love the crawlspace for it's removing potential lateral stability and friction from the inside. The top of the stem walls would be braced by the floor deck as phamENG mentioned earlier.

So like shown below then? How do we deal with vertical tolerance in the piles? Get them to nail it? Install some yucky shims?

 

[phamENG]

Yes, that's the section. IBC, not IRC. Sorry.

Yes - P-X is a common designation used around here for pile caps of X number of piles.

Perhaps I read that clause for houses a little too liberally. I don't usually limit myself to walls, but let interior pier lines with grade beams fall under it, too. The difference between a couple courses of CMU and a wood framed wall and a couple of courses of CMU in a pier with a girder and a wood framed wall just doesn't seem to make that big of a difference for me, especially if I locate piles underneath the piers. If somebody disagrees, by all means say so.

It's usually not too hard for them to hit an elevation pretty accurately. There's usually some amount of cutting and welding for the plates anyway, so if they hit their torque with 3' sticking out, they just need to cut it off at the proper elevation and weld the plate on. And, in a pinch, shims can get it done.

 

[KootK]

I don't usually limit myself to walls, but let interior pier lines with grade beams fall under it, too.

One of the options that I'd considered was indeed just to do the interior line as a footing and stem wall so that I could use that same provision. Thanks for all of your help so far.

 

[AskTooMuch]

We've installed hundreds of helical piles inside our plant, vertical tolerance is not much an issue. Helical piles contractor uses laser level for the elevation.
They can also cut the piles and weld the cap to the shaft.


You may need still to meet minimum depth even if you hit the torque. Because the lateral capacity of helical piles depends on the length of shaft and diameter.

 

[phamENG]

You may need still to meet minimum depth even if you hit the torque. Because the lateral capacity of helical piles depends on the length of shaft and diameter.

Agreed. Unfortunately, though, where I am residential projects with helical piles will typically opt not to use a geotechnical engineer after the helical installer convinces them that the torque conversion equation is all knowing and all powerful.

 

[jayrod12]

On a deck that was done recently, the pile supplier had adjustable saddles. I'll send a picture if I can find one.