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Micropiles embedded on different soils

Micropiles embedded on different soils

Micropiles embedded on different soils

(OP)
Hi
Is it OK to embed micropiles on different soils knowing that they usually don't work as tip bearing fondations and that some piles are to be embedded on a weathered rock while the others on dense sands and gravel. Also there are no group effects

RE: Micropiles embedded on different soils

I would think that any soil you can safely embed them in... but you have to be well aware of potential differential settlement, and make allowance for it in the structure design and detailing.

So strange to see the singularity approaching while the entire planet is rapidly turning into a hellscape. -John Coates

-Dik

RE: Micropiles embedded on different soils

(OP)
Thank you dik 🙂
Awaiting additional feedback

RE: Micropiles embedded on different soils

One way to evaluate that differential settlement is to generate p-z springs for ach pile and apply them to the structural model.

RE: Micropiles embedded on different soils

You might have a difference in settlement. The geotechnical engineer can estimate the differential movement and the structural engineer would have to evaluate if the structure can handle the movement. Typically I'm using micropiles for larger structures so I tend to keep all the piles embedded into the same material.

RE: Micropiles embedded on different soils

Settlement calculations are a guess at best, especially when dealing with trying to calculate the settlement of two different soils. If your structure is sensitive to differential settlement, you may want to consider preloading the piles to "take out" any settlement effects.

RE: Micropiles embedded on different soils

Quote (Settlement calculations are a guess at best)


That's my experience... same with concrete deflections... I was hoping that a 'bunch' of geotekkies would jump into this. I don't know what a collective of geotekkies is called? A herd, flock, cackle? Hopefully not a murder. ponder

So strange to see the singularity approaching while the entire planet is rapidly turning into a hellscape. -John Coates

-Dik

RE: Micropiles embedded on different soils

An "argument" of geotechs is my suggestion for a group name.curse

www.PeirceEngineering.com

RE: Micropiles embedded on different soils

Not a bad idea PEinc.

Dear structurals - pretty much all geotechnical related "calculations" are educated guesses.

That being said, if you have enough experience with load testing micropiles in the materials in question, you certainly can make an educated guess/calculation of what your differential settlement will be.

RE: Micropiles embedded on different soils

You can always design the micropiles for friction bond based in the weakest soil penetrated by the bonded length. I've never considered end bearing in my micropile designs.

www.PeirceEngineering.com

RE: Micropiles embedded on different soils

Quote (killswitchengage)

Also there are no group effects.

IMHO, for friction micropiles group effect is possible since group effect is based on the pile size / layout geometry, not soil properties.

RE: Micropiles embedded on different soils

I dont think it will be a big issue when you consider that the tip is so small compared to the shaft area and the mobilization of end bearing required to get capacity. I would guess that your differential is less than 10mm.

I have never seen a foundation that has to consider group effects. Only in very limited situations are we forced to space piles at less than 2.5-3d. Otherwise its not an issue.

RE: Micropiles embedded on different soils

(OP)
Thank you all for the wonderful debate
I should point out that large scale tests were conducted using service loads.
The micro pile embedded on the rock gave high vertical capacity with minimal settlement while the one emebeded on the dense sand produced a 10 MM settlement for a 300 MM diameter pile and a lower bearing capacity, this is why I am concerned

That being said they did use vertical and horizontal springs for the overall design of these micropiles.

RE: Micropiles embedded on different soils

So the question is, can the structure tolerate approximately 10mm of differential movement? Unless it’s a bridge with separate substructures, you’ll likely have to use the same allowable load on each pile.

RE: Micropiles embedded on different soils

Quote (An "argument" of geotechs is my suggestion for a group name.)


Sounds great... thanks.

So strange to see the singularity approaching while the entire planet is rapidly turning into a hellscape. -John Coates

-Dik

RE: Micropiles embedded on different soils

I'd be reluctant to use rock and softer soil at the same time unless structure was detailed for it... I'm not a geotekkie, but I would try to avoid that.

So strange to see the singularity approaching while the entire planet is rapidly turning into a hellscape. -John Coates

-Dik

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