Pile loading test

[AnnaG]

Hello,

I am tring to calculate loading test of small scale pile in ABAQUS CAE. Results which I get are rediculus. I am afraid it can be connected with invalid definition of geostatic state of stress (gravity g=10 m/s). I checked the units but there is ok with them.

Axisymmetric model dimensions:

Part-1 : 0.5m x 1m (horizontal x vertical) with 'hole ' for pile 0.035m x 0.45m (horizontal x vertical)

Part-2 : 0.035m x 0.45m (horizontal x vertical)

My dry sand is modelled with Mohr-Coulomn

density 1450kg/m^3

Young modulus E=40e6 Pa

Poisson ratio ni=0.3

friction angle fi=33deg

dilatancy angle psi=10deg

cohesion c=100 Pa

Pile properties (Elastic):

density 2400kg/m^3

Young modulus E=20e9 Pa

Poisson ratio ni=0.3



I define initial state of stress( EALL - set which is whole model soil+pile) by

*initial conditions type=stress, geostatic
EALL, -14500, -1, 0, 0, 0.5

When I check Frame-1vertical stress is like I defined and no vertical dispalcement occures

Frame-2 vertical stress changed (caused by the weight of pile) and significant values of displacement occured (also S12 and CSHEAR1 are not equal to 0)

Interaction between soil-pile (created in Initial step and propagated to all): tangential - penalty - friction coefficient 0.35

Two steps:

Step-1: Static, gravity load (whole model)

Step-2: Static, gravity load(propagated tron previous step) + displacement on the pile top (d=0,05m)



Problem is that the concentration of vertical stress is in soil under pile tip not as I expected in the pile head.

Does anybody know what can caused this kind of behaviour? and what is more important how to fix it?

Thank You in advance

Regards,

Anna

 

[Geotech2011]

Hi,
Check your Boundary conditions.

 

[AnnaG]

XSymmetry - left side (axis)
Blocked Y - on the bottom
Blocked X - right side

 

[Geotech2011]

Hi Anna,
has your problem been solved?

 

[AnnaG]

Unfortunately not :l

 

[Geotech2011]

I read your problem which you explain above, but I couldn't understand well that, what's your aim of this model. If it's possible, please let me know your purpose of this simulation. I'd like to help you and solve your problem.
I have some experience in penetration pile .... in soil with Abaqus.

 

[AnnaG]

This is my cae file.
I want to model loading test of pile. So loaded it till failure (in this case I guess in soil).

Thank you in advance

 

[Geotech2011]

Hi Anna,
Find the Attached(Inp file) which is analysis of pile driving. Hope, solve your problem.

 

[AnnaG]

Hello,
I hope it will solve my problem. Where can I find this Inp file?
Thank You

 

[Geotech2011]

Hi Anna,
Please find the attached.

 

[AnnaG]

Thank You one more time I am tring to analyze your file. Hope will find my mistake.

 

[AnnaG]

I analyze Your input file but unfortunately, I didn't find solution for my problem

Would You be that kind and send me a cae file with simulation of loading test for any soil and pile parameters. I think My mistake is hidden in contact definition but I am not sure.

Thank You in advance
Anna

 

[Geotech2011]

Hi,
I'm sorry about that, but I haven't any other cae file which be close to your problem. By the way, what's your definition of soil/pile interaction?
I think you should define contact interaction based on slide line formulation. Define surface to surface interaction and choose tangential behavior and then select penalty or Lagrange multiplier for friction formulation.

 

[Geotech2011]

Hi again,

I read your explanation of your simulation once again, and I think you should change the type of your analysis step from static to soils. It might be solve your problem to get more acceptable results. Try it. Good luck

 

[AnnaG]

I checked for soil step but it doesn't change anything :/

 

[aliasgere]

You need to remove the pile from the geostatic stress. Just apply geostatic stress to the soil block.

Also, how have you modelled your interaction. Are you using effective stress analysis?

 

[AnnaG]

You mean initial geostatic condition just to soil (nothing define for pile), right?

Step-1: Static, gravity load (whole model or also just soil?)

Step-2: Static, gravity load(propagated tron previous step) + displacement on the pile top (d=0,05m)

I'm trying to model dry case so there is no difference between effective and total.

Interaction: soil-pile
- surfaces: Master: pile shaft and tip, Slave: soil which is directly in contact with shaft and tip of pile

- created in Initial step and propagated to all: tangential -> penalty -> friction coefficient 0.35

 

[aliasgere]

Yes, geostatic stress is for the soil only. Do not include the pile.

Gravity is for whole model so that's correct.

Do you not have normal contact behaviour (hard contact and penalty constraint enforcement method)?

What value of poisson's ratio are you using?

 

[aliasgere]

Sorry read your earlier post about poisson's ratio.

 

[Geotech2011]

Hi Anna,

I have a problem which is close to your problem roughly. would you please let me know has your problem (stress concentration) been solved or not. If yes,I was wondering if you could help me.

Thanks,
Geotech2011