Laterally loaded pile analysis 2

[Awre]

I am analysing the lateral capacity of steel pipe mono pile. The pile is in a marine environment and loaded at (Elev. +9 MLW), the ground elev. is at (Elev. -19 MLW), the pile tip is at (Elev. -120 MLW). The pile O.D. is 5 feet. I have couple of software: FB multi pier and Lpile which I see both are capable to analyze a single pile. I have couple of questions:

- Which software is more aproperiate for the analysis?

- Both programs require input for subgrade modulus (lb/in^3)for the clay soil (soft, stiff, or V.stiff). Is there any approximate values for the subgrade modulus for each of the above soil types?

Thanks

 

[ishvaaag]

Usual values are (ks30)

0.5 kgf/cm3 soft soils
4.0 kgf/cm3 firm soils
12.0 kgf/cm3 very stiff soils

Source is Albert Fuents, RC Buildings book, which does not indicate (but must be) being ks30 values (1 ft square plate)

I have also found that to mimick the actual (probabilistic) behaviour for ordinary buildings in non extremely problematic soils, and with mats, the ks30 without any scaling for foundation size may give a better approximation than applying the scaling. Have no clear idea on how this will relate or how to be considered unto your pile intent.

 

[rowingengineer]

Just a thought, offence indented.

Why bother analysing this pile with a high level computer package when you are going to approximate (guess) the subgrade modulus? Or maybe you are waiting for the geotechnical report and just want to get something happening


Arguing with an engineer is like wrestling with a pig in mud. After a while you realize that them like it

 

[asixth]

I have found that estimations of the subgrade modulus doesn't have much bearing on the design actions on the pile, such as moments and shears that are caused from passive soil resistance. The peak moments are actually very similar to the answers that you can obtain from a simplistic Brom's approach.

Computer analysis assuming elastic-linear deformations of soil does give the engineer an 'answer' of the lateral displacement at the pile-head. I have never seen anyone in my office check the displacement at the pile-head except for myself, mainly because of the lack of useful soil-structure information that is provided by geotechnical engineers in my part of the world. I have found the geotechnical engineers in Australia to be lacking technical knowledge. I had a geotechnical engineer say to me the other day that a particular rock had a 350kPa (50psi) allowable bearing capacity or a 2250kPa (325psi) ultimate bearing capacity. That is a factor of safety of 6.5...

 

[Awre]

ishvaaag - Are these values apply for submerged soils?

asixth- but is your observation applies if the pile is 5' diameter

Thanks everybody

 

[studio13]

Personally I use lpile and it should give you the model you are looking for. This is mainly because that's what I'm used to using. In reality you probably can't go wrong using either one. As for input values, under the HELP section in the Lpile program you can look at typical value ranges for each type of soil for above the water table and for submerged. Its a good starting place. As mentioned the subgrade modulus will likely not have a huge affect on the outcome. But I'd recommend that since you are unfamiliar with the program and how it works, you might try a wide range of values and see just how sensitive the model is to that value.....this way you can decide for yourself if you need to have more input on the proper value. You might try that with a few different parameters to better understand the sensitivity of the model and the way the program works. The biggest thing with Lpile is make sure you use all the proper units.

 

[asixth]

adfo,

My post wasn't the most helpful in answering your question. I don't think results would vary because of the size of the pile because the soil reaction is taken over a rectangular area so the results should be linear. I.e. larger piles, more soil resistance.

I am going to work now so I will post so information on soil subgrade modulus that my local DOT sent to me.

 

[ishvaaag]

As given in the book surely were for ordinary soils, I don't think Fuentes was thinking in submerged; of course for vertical loads.

 

[Doc09]

Lpile has the following values in a table:

8100 KN/m3 for Soft Clay
27000 for medium stiff clay
136000 for stiff clay
271000 for very stiff clay
540000 for hard clay

the above values are reduced for cyclic loading applications:

----- KN/m3 for soft and medium stiff clay
54000 for stiff clay
108000 for very stiff clay
215000 for hard clay

Hope that helps.

 

[asixth]

The first paper is one that was given to me by my local DOT regarding typical subgrade modulus's of particular soils.

 

[asixth]

An this one is from a geotech's report that I received once, similar soils to what you are after.

 

[swearingen]

You say it's a marine environment. Is it a river bed? Lake? The Gulf of Mexico? There are other things to be considered. For example, if it is a river bed, you'll need to reduce the depth of the resisting soil due to scour. How much scour? You'll need to know the depth fluctuation and velocities...


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