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Correct way of designing the pile for layered soil

Correct way of designing the pile for layered soil

Correct way of designing the pile for layered soil

(OP)
Dear All,

I'd like to know what is the correct way of modelling the piles? Based on the google research and design books, I can understand that it's still open area of research. In my case I have layered soil which is composed of: clay + dense sand + clay; I'm in dilemma on which model basis to model the piles as cantilevered column which takes the lateral soil pressure or model the piles as frame object(column) and apply the springs laterally ?

I've seen that both techniques are used for modelling but I can hardly judge which is correct and close to the reality, IMHO with 1st technique cantilevered columns seems like overdesign but since I have non-cohesioned dense sand stratum it supports the fact that it can not be designed as horizontal spring. On the other hand I've seen in the book(Programming teh Finite Element Method 4th ed, Smith, Griffiths; Program 4.3) that linearly increasing pile stiffness(that is springs) is recommended for general solution.

I'll appreciate your guidance !!

Regards,

RE: Correct way of designing the pile for layered soil

The cantilevered column method has been widely accepted as valid for a long time, even in layered soils. The key to making it accurate is to determine the pile's point of fixity - not easy to do. Fortunately, for a lot of soil types and combinations the point of fixity varies over a surprisingly small range - typically from 5 to 10 below the ground surface.

See the following two documents on this page of my website http://www.slideruleera.net/TreatedWood.html :

"How to Determine Lateral Load Capacity of Piles"

In this paper, note that Davisson & Gill who authored an often referenced 1963 paper "Laterally Loaded Piles in a Layered Soil System" agree with point of fixity method. (I have not found a copy of the Davisson & Gill paper).

"Laterally Unsupported Pile Study"

Both are old and out of date. The only real change is that now computers are now readily available to quickly solve more sophisticated, but not necessarily more accurate, mathematics.

www.SlideRuleEra.net idea
www.VacuumTubeEra.net r2d2

RE: Correct way of designing the pile for layered soil

(OP)
Thanks SlideRuleEra for enlightment,

Can you shed some light on which chapter should I focus if I choose to design the pile as column as per the IBC03 / ACI318-05. Especially the transverse reinforcements, because the best thing that I found was ACI-318/05--21.4.4 chapter in code.

Also I would like to know how major and minor shear reinforcements are determined. For example, If I use spiral or circular confinement bars and if major shear reinforcement area is adaquate for minor axis also, then is that major axis reinforcement can be used for the minor axis without supplying the additional reinforcement for minor axis?

Regards,

RE: Correct way of designing the pile for layered soil

joehigashi - I assume you are talking about DRIVEN concrete pile. ACI 318 is not intended for design of piling. A pile has to be much more than a cast-in-place column. A pile has to be picked up (typically from a horizontal position), handled, and then withstand the stresses of impact driving. ACI 318 does not address these requirements.

At one time cast, reinforced (not prestressed) concrete driven piling were common. They became obsolete over 50 years ago when they were superseded by cast, PRESTRESSED driven concrete piling. Design of the prestressed piling is outside of ordinary structural design practice. Many (USA) state departments of transportation have their own design criteria, here is a typical example for the state of Florida:
http://www.dot.state.fl.us/rddesign/DS/12/Ser/Squa...

Also, you may be able to find other information from the Precast / Prestressed Concrete Institute:
https://www.pci.org/

Note that spiral ties are almost universally used in piling instead of circular ties. Experience, especially in earthquakes, has demonstrated that spiral ties are superior.

www.SlideRuleEra.net idea
www.VacuumTubeEra.net r2d2

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