Tangent / Secant/ Drilled Shaft wall Modelling in Lpile 2

[Jalthi]

I was wondering how one would model a drilled shaft wall in Lpile to determine the lateral deflection and depth of embedment.

I would model the height of the wall as part of shaft that is unsupported by earth. Then apply lateral earth pressure on the unsupported part. In other words:
1. Distance from Pile Top to Ground Surface = Height of the wall
2. Check "include distributed earth loads" and input load that represent active earth pressure condition.
3. Then the first soil layer starts from the dredge level.

Please comment if you would agree with this approach. Thank you.

 

[FixedEarth]

Jalthi;

Let us hold on for a moment on the software use. For a laterally loaded drilled shaft, you can do hand methods using Teng, Budhu & Davies, Broms, Brinch Hansen etc. It may only take you 1 hr to do it this way. You will develop a feel for it and then later you can check it using software. This manual method will come in hand in the field. For example, if you are observing drilled piers that are used as a retaining wall, you will be looking for embedment depth that is 1.25 times the retained height. If it is vertical load, you will realize that this does not affect embedment or lateral deflection as much as a moment or a lateral laod would. As Hugh Brooks of RetainPro says, "this will be a good excercise". One other benefit of manual method, use the equations from the books or papers and program it into a spreadsheet or a mathcad.

 

[SixDegrees]

I would not use LPile for a wall because the P-Y soil model upon which is is based is specific to the geometry of soil-pile interaction. In particular I don't believe it will take into account differential water pressures that may exist with a wall. I recommend developing classic active and passive lateral earth pressures (and water!), and do a free or fixed cantilevered wall solution.

 

[Jalthi]

SixDegrees:

Your point is noted. That is why I model the embedded portion of the shaft in Lpile. The cantilever wall portion is assumed to be standing above the ground where I apply distributed pressure along its length that represent active earth pressure with pore water.

Do you think it is a reasonable approach?

 

[SixDegrees]

Section 2.1.4.7 of the LPile Technical manual refers to the point that I am making. You will need to come up with a modified P-Y curve that reflects the soil resistance versus deflection for a wall, rather than a pile I(the built in ones are for piles). I don't recall ever coming across P-Y curves for walls that can be used in LPile so you'll need to do some investigation to find the Wall P-Y curve that you feel comfy with.

Ensoft Inc. may have done some of the leg work for you if you check out the PYWall software that they have, or give them a call and see if they can provide some references.

 

[cyclinggeo]

I'm not sure I'd use L-Pile for this. L-pile was originally developed for long-slender steel pipe piles offshore...additional research since then, but pretty specific to these constraints.

 

[irawanfirmansyah]

Jalthi,
I believe that you can use your model to analyze drilled shaft wall in LPile. Height of wall = distance from top of pile to ground surface, and the remaining length of pile as embedded portion of the wall.
But, remember that p-y curves for a continuous wall is weaker than those of a single pile. You have to multiply the p with a reduction factor.Assuming a wall as contiguous piles and adopting the Reese method for calculating p-y reduction factor for a pile group, I come up with a reduction factor of 0.25.