L-Pile Input Data 5

[annabot]

Hi,

I have just started using L-Pile, and am a little bit confused about the soil data I need to input.

My first questions is, I dont quite see all classes of soil in L-pile, so what can I use for what?

My second questions is, where in a geotech report can I get the cohesion, and unit weight of the soil? I have seen some geotech reports where they have a table with all the info I need for L-Pile is in it, which was really convenient and helpful, but recently, I have recieved two reports that didnt have that. So I am not sure if the reports just arent complete, or is it hidden somehwrere and I just dont know?

My third question is, how do you interpolate the STP values, for example what does "STP-N Value of 30" or "STP-N Value ranging 58" means?


Thank you!

 

[BridgeEI]

The help manual should list all the soil conditions that are available. The geotech reports I've dealt with never have the cohesion or unit weight. Its an extra test or two that would have to be ordered. What's the point of getting them though, the geotech would just use the lower bound values anyways. N is the number of blows per foot I believe. Take a look at a soils book and verify.

 

[annabot]

Thank you for your help. I will check out the help manual. Is there a book that you recommend, that I can get these tables and info, for soil classification, from?


Thanks!

 

[jgailla]

In my area of the US the geotech usually runs the L-Pile program because they have more knowledge of the soil parameters.
The report (or an addendum) would provide lateral movements to the structural engineer.
This is often an iterative process requiring communication between the structural and geotechnical engineer.
You should probably discuss these issues with your geotech.

 

[BridgeEI]

We've never had the geotech run the program. When I use it, I'm just determining a point of fixity for the pier design. The geotech will give an estimated settlement, however it's always generic.

If you look in the manual, it will give the different parameters for each soil type and recommended values. It will give a range of XX to XX and so I always use the lower value which is sufficient for what I need.

You just need to thumb through the manual really and you can find almost anything you need there. That and a soil structure interaction class is really beneficial.

 

[annabot]

Thank you!

 

[FixedEarth]

At the end of your analysis, do you know what range of lateral load capacity you should be getting? If not, try to get an experienced colleague to show you the ropes. It took me about 2.5 years to get comfortable with laterally loaded piles and piers. It is very complex. However, either a soils or a structural engineer can do the analysis, provided they understand soil structure interaction.

To start your learning journey, get a copy of Bowles "Foundation Analysis & Design", 4th or 5th edition. This book explains SPT values and analysis of laterally loaded piles and piers. Later on, if you find you are doing these analysis more frequently, then get a copy of "Single Piles and Pile Groups Under Lateral Loading", 2nd ed. At our firm, we use Lateral Foundation software. Good luck.

 

[annabot]

Thank you FixedEarth.

Unfortunately, I am in a very bad position!! I graduated less than a year ago, got hired to work with the senior SE, but couple of months ago they let him go, so I am pretty much left on my own. I have been doing a lot of online researching and reading, so hopefully I can pick it up fast, but it is still a lot of pressure! I don't know why I didn't think of joining this forum any earlier, but thanks to all of you, now I feel like I have a support system!

I will definitely reach for those books.

Thank you so much for the help!

 

[FixedEarth]

Darn. Look at the good side- you will be a senior engineer sooner than you planned it!

Attached are rough guidelines to check your final output. Apply a factor of safety of 2.0 on your chart values. These are from "Soil Engineering: Testing, Design and Remediation", F.H. Chen, only edition.

 

[annabot]

God, I hope so!!!

Thanks for all the help I am sure I will be back soon with MANY questions!!

 

[pelelo]

Thanks Fixedearth for uploading that chart about estimating soil lateral capacity.

things get more difficult when you have several cohessive and cohessionless soil strata. That´s when LPILE is better to deal with.

annabot,

You are right, not all soils are listed in LPILE. At least I use LPILE 5.

For instance you don´t have soil classified as gravel. In this case I use it as sand.

Also if your example you have a medium clay, LPILE has either soft clay or stiff clay with and w/o free water. I usually use the soft clay option, being more conservative, of course.

 

[FixedEarth]

Good point Pelelo. You should try this program:

http://www.soilstructure.com/lateralfoundationsoftware.html

It takes into account soil layering, and assigns the lateral SG modulus automatically. The structural engineers like it because you can combine the loading and the soils description into one entry format.

 

[pelelo]

Just for curiosity,

Have you ever compared lateral foundation software vs LPILE results?,

Are they similar?

 

[FixedEarth]

Yes, I did. On Clayey sites they give similar results. On granular sites, Lateral Foundation gives slightly more conservative results (more deflection)-I think this is because the lateral subgrade values have been limited a bit.

The main difference is the analysis approach. Lateral Foundation program uses beam on elastic foundation method (Hetenyi) with lateral subgrade modulus values. I believe this to be the second most accurate way of performing lateral loaded foundation analysis.

The method proposed by Budhu and Davies,1986? I think, is the best approach because the soil is continuously surrounding the pile/pier but spring analogy assumes springs separated by some distance.

I have also compared Lateral Foundation results with Bowles Lateral Pile method. These two programs yield very close results. So far, I have used Lateral Foundation on Silo foundation support, sign support, short span bridge, retaining wall on pier foundation and 3 story residence. The good thing about it, it only takes me 15 to 20 minutes to get my results. Few years ago, I used to grind teeth when I had to do Lateral loaded pile and Liquefaction analysis. Not anymore!

 

[PEinc]

AllPile by CivilTech Software has a good soil properties input screen. See attached screen shot. The program uses LPile for lateral analyses and also does other analyses.

www.PeirceEngineering.com