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RE: LPILE or Other (Laterally Loaded Pile Analysis)

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Title: RE: LPILE or Other (Laterally Loaded Pile Analysis)

Bill,

Another good source if FHWA-IP-84-11 Handbook of Piles and Drilled Shaftes Under Lateral Load (NIST # PB85-201085);  it contains representative values of epilson-sub-50 as follows:

Soft Clay = 0.02
Medium Clay = 0.01
Stiff Clay = 0.005

You'll find many geotech's using these general values based on soil classification instead of doing specific triaxial tests to obtain the value.  You can easily do a parametric study using COM624 to see how altering each variable affects outcome.  If I remember correctly, the episilon-sub-50 value drastically affects pile head deflection (in the case of a free pile head). 

Have you seen anything on drilled piers into limestone or soft rock ?

Robert

Robert C. Rogers, PE
Senior Structural Engineer
A.M. Kinney, Inc.
Consulting Engineers / Architects
150 East Fourth Street, 6th Floor
Cincinnati, Ohio 45202
PH: 513-421-2265, ext. 125
FX: 513-345-1318
rogersr(--nospam--at)amkinney.com
www.amkinney.com


-----Original Message-----
From: Bill Polhemus [mailto:bill(--nospam--at)polhemus.cc]
Sent: Wednesday, March 13, 2002 12:52 AM
To: seaint(--nospam--at)seaint.org
Subject: RE: LPILE or Other (Laterally Loaded Pile Analysis)


That's an idea, but to tell you the truth I'd rather do this analysis myself. I don't mind having the geotech giving me the data needed in the report but I like doing the foundation design myself not having it done for me.

To tell the truth I have a nice "closed form solution" for doing a pretty close estimate of the pile head movement and (especially) the maximum moment in the pile. It is based upon a paper that was presented a few years ago at the Texas Section ASCE meeting, and I've received a copy of it from the guys who put it together.

Essentially, they took several hundred LPILE runs, and collated the data then did a very fancy curve fit. The result is a ponderous-looking equation which nevertheless is easy to solve using e.g. Mathcad's ROOT function.

But there are a few limitations on their method and the authors state that it is for "preliminary design" and should be followed-up with a more extensive analysis using LPILE or similar.

One of the limitations is that it assumes a value for (50  (that's Epsilon-sub-50) of 0.01. The soil report I'm using recommends a value of 0.005. I'm not all that conversant as to how sensitive the analysis is to a change in the value of (50  (Epsilon-sub-50), but I wanted to explore that for myself.

It seems to me, btw, that since (50  (Epsilon-sub-50) is defined as "the strain at one-half the ultimate shear stress of the soil" that a value of 0.005 would indicate a STIFFER soil than that of 0.01 and thus any analysis would be more conservative at the higher value, but I don't know the details.


William L. Polhemus, Jr. P.E.
Polhemus Engineering Company
Katy, TX, USA
Phone (281) 492-2251
FAX (281) 492-8203
email bill(--nospam--at)polhemus.cc