"Curved" conductor pipes - Driveability

[nicolini]

I was asked to evaluate the driveability of "curved" conductor pipes for the offshore industry.
Even if I'm used to analyze the driveability of offshore
foundation piles, that are assumed to be perfectly straight, I was not able to find any paper or book where a calculation method for a "curved" pipe pile or conductor is given or explained.
I am looking for infomation, paper or anything alse to help understanding this problem.
Thanks.

 

[GeoPaveTraffic]

I've never heard of anyone intentionally driving a curved pile. Good luck.

 

[Focht3]

Ditto. That will probably require significant modeling in order to arrive at an answer - using at least three different - and unrelated - analytical tools. And your answer will probably be, "It's possible, but unpredictable and quite risky."

Where is the site?



Please see FAQ731-376 for great suggestions on how to make the best use of Eng-Tips Fora. See faq158-922 for recommendations regarding the question, "How Do You Evaluate Fill Settlement Beneath Structures?"

 

[nicolini]

hi.
to GeoPaveTraffic:
Believe me, it happens, and it is sometimes used for the offshore industry. They are adopted to guide the initial part of the drilling tool in cases where the well is inclined with respect to the vertical axis, in order to reach an oil layer not below the platform vertical.

to Focht3:
I'm sorry, but in this case also (You alredy helped me yesteday), the site is generic, as I was asked by the Client to prepare a "state of the art" of what exist on the topic, in order to participate to offshore project involving "curved conductors", that at present we cannot deal with.
All I have until now is an early paper, published by OTC (the paper is #OTC 2309), but it is a bit old, being dated 1975......
I hope some more has been published in recent years.

bye.

 

[Focht3]

Who authored the paper? (I don't have ready access to the OTC papers anymore...)



Please see FAQ731-376 for great suggestions on how to make the best use of Eng-Tips Fora. See faq158-922 for recommendations regarding the question, "How Do You Evaluate Fill Settlement Beneath Structures?"

 

[nicolini]

Dear Focht3,
the paper is:
"Driving Analysis for Initially Curved marine Conductors", by F. Joseph Fisher, Shell Oil Co., OTC 2309, 1975.
The problem formulation seems to be a bit complex, as transverse force (shear) and bending moment behaviour need to be added to the classic axial force versus axial deformation model adopted by the classical 1D wave propagation theory for straight piles originally stated by Smith.
For "normal", straight piles I use the commercial software GRLWEAP, that does not allow for curved ones.
I am wandering if, below a limit curvature of the pile, the problem cound be treated by increasing the pipe axial deformability to account for the bending deformability (the one due to shear con be neglected, I believe).
What is Your opinion about that?

 

[Focht3]

I think you are walking barefoot across a dirty floor covered with broken glass, while the room is on fire behind you.

I don't mean to be such a pessimist, but this is a problem that desperately needs a number of fully instrumented field tests in order to figure out what's going on. Axial stress, flexure and torsion in the conductor; non-linear soil response in the axial (t-z curves), lateral (p-y curves) and torsional (special t-z curves) modes. (Minor eccentricities will probably induce fairly major torsional effects.) All that under a transient dynamic loading (i.e. pile driving) which isn't particularly well understood to begin with. That's a pretty tall order; I don't know of any commercial software capable of addressing this problem.

I strongly suggest that you contact Bill Isenhower at Ensoft and get his comments. Bill received his PhD at Texas under Lymon Reese, and now works with him as well. He may have a few tricks up his sleeve that can put you on the right track. If he doesn't, I don't know who would -



Please see FAQ731-376 for great suggestions on how to make the best use of Eng-Tips Fora. See faq158-922 for recommendations regarding the question, "How Do You Evaluate Fill Settlement Beneath Structures?"

 

[nicolini]

to Focht3:
Yes, I think so, the picture You made is actually reliable.
The good new is that information are coming back to me and it seems that if the pipe curvature is not high, the problem is non significant. They tell me to think about the fact that some pipe piles (with small diameter, I suppose) adopted in the offshore industry do actually penetrate into soil with a non predicted curvature. Nobody seems to have reported problems during driving.
This is good and is confirmed by the Paper I told You, but is not enough for desing.
Ok, this is what I understood until now.
I'll keep this thread alive as new information arrive to me, if of interest.
Bye.

 

[Focht3]

Yes, we are interested! Keep us posted -



Please see FAQ731-376 for great suggestions on how to make the best use of Eng-Tips Fora. See faq158-922 for recommendations regarding the question, "How Do You Evaluate Fill Settlement Beneath Structures?"

 

[RDenis]

Hi,
Just few words to say that I am going to work on this topic in the next weeks and that I am interesting with any advices on this subject. As far as I know on the subject, we are going to backfigure the energy lost during previous installation of curved conductors and then perform a standard pile driveability analysis with a reduced hammer energy.

 

[Zambo]

I assume that this is a common situation in the off-shore industry. The pile I guess forms the annulus through which a vertically directional drilled conductor (flow pipe) will be installed. This annulus will therefore not be carrying loads as a pile, but will mainly be a casing for the flow pipe. Or am I mis-understanding the job in hand.

Zambo

 

[nicolini]

to RDenis:
wow! so I'm not alone in this world...........

I'll continue my research and keep You informed of results I find.
Anyway, performing driveabilty analyses assuming a reduced
hammer energy (i.e. reduced stroke, I suppose) is prudential
as far as feasibility of driving is concerned.
But if soil resistance to driving is high, what about the
stresses in the pile steel walls?
You may be requested to increase the hammer energy and/or
to switch to a more powerful hammer.
This may be a problem, as
conductors are usually small diamters pipes (say: 20÷30 inches) with a limited wall thickness (say: less than 1'').

Moreover, if hard driving occurs, what about the reactions at the conductor guides placed at deifferent elevations on the jacket?

to Zambo:
yes, You are partially right. Conductors are used simply as a guide for the drill bit and to sustain the excavation where usually soil is softer. They also carry only their self-weight. The problem is not this.
It is to predict the resistance mobilized during installation by means of driving with an appropriate hammer.
Driving may request to modify the geometry of the pipe to be installed (first) and (second) You need to select the appropriate hammer able to perform the installation.

bye

bye