Consideration of Weight of Soil Plug in tubular Steel pile
Consideration of Weight of Soil Plug in tubular Steel pile
(OP)
Hello All,
In the case of open ended, tubular steel, friction piles, should we consider the weight of soil plug, inside the pile, as demand on pile ?
Can it not be argued that the soil has done necessary readjustment to itself,whilst driving and thus the weight of plug has the same status as soil outside the pile
and demand on the pile is purely from superstructure?
Rgds
In the case of open ended, tubular steel, friction piles, should we consider the weight of soil plug, inside the pile, as demand on pile ?
Can it not be argued that the soil has done necessary readjustment to itself,whilst driving and thus the weight of plug has the same status as soil outside the pile
and demand on the pile is purely from superstructure?
Rgds






RE: Consideration of Weight of Soil Plug in tubular Steel pile
If the soil is clay, I suppose you could make a case that some portion of the clay "sticks" to the pile wall, and therefore transfers the soil load from the bottom of the soil plug to the wall of pile. I would probably assume this effect to be negligible on pile design.
I would be interested to hear from any geotechs out there if this does in fact occur and if so, is there any significant impact to design?
RE: Consideration of Weight of Soil Plug in tubular Steel pile
From that statement, IMHO, the soil plug is important for developing load capacity - in that type soil. Not a demand on the pile but a contributor toward improved performance.
You can download the Bethlehem book at this page of my website, see page 13: Link
www.SlideRuleEra.net
www.VacuumTubeEra.net
RE: Consideration of Weight of Soil Plug in tubular Steel pile
Thank you guys for the suggestions and SlideruleEra for kindly sharing the resources on Pile Design.
The effect of self weight is not negligible, as I have a large dia pile with a lengthy penetration.Let me illustrate my case with numbers.
I have a pile that is 1.8m in dia and 90 m deep pen in soil.
The weight of the plug is pi/4 * 1.8m^2 * 90m * (2.00-1)t/m^3*2.00(F.O.S) = 457 MT.
Which is quite substantial increase in demand on pile.
I have not come across anything in literature and geotech books which deals with this topic in some detail.
I have an argument developed to justify NOT taking the weight of plug.
My argument is that self weight of soil and plug gets adequately supported by rearranging the soil matrix during driving.
It is as if I have manufactured a big piece of rock at foundation point.
If indeed there was real rock at foundation I dont take the weight of rock in determining the demand on the foundation.
In short Weight of plug is supported by soil matrix rearrangement by driving, superstructure loads are supported by "pile soil composite structure".
Rgds
Angre
RE: Consideration of Weight of Soil Plug in tubular Steel pile
After driving, the weight of plug may neither create a the load on the pile nor contribute to support of the load.
Am I misunderstanding something?
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RE: Consideration of Weight of Soil Plug in tubular Steel pile
You are right that if plug is formed at the toe, soil will not enter the pile.
This though is not easy to ascertain(and convince others).We cannot justify as to when and when not a plug gets formed.
So to be on safe side, it is assumed that all of the pile is filled with soil.
Rgds
Angre
RE: Consideration of Weight of Soil Plug in tubular Steel pile
RE: Consideration of Weight of Soil Plug in tubular Steel pile
Edit: Another option could be to ask Dr. B.H. Fellenius for his opinion. I see on his website that he does respond to emails: Link
www.SlideRuleEra.net
www.VacuumTubeEra.net
RE: Consideration of Weight of Soil Plug in tubular Steel pile
RE: Consideration of Weight of Soil Plug in tubular Steel pile
So to answer your question, the plug weight may be neglected.
If you would like to test this, do a cone penetrometer in the center of the pile before driving and after driving to determine the difference. Cheap compared to driving a 90m pile!
RE: Consideration of Weight of Soil Plug in tubular Steel pile
The formation of plug cannot be ruled out.
Such "plugs" can form even in diameters as large as 20m.Iam thinking of cement silos and design of silo walls.
Rgds
Angre.