What is this error in abaqus when define material with cam-clay 1

[mojtaba pourgholami]

hello
I'm working on foundation consolidation in Abaqus
and I define my clay properties with cam-clay plasticity
I get this error in analyzing
The sum of initial pressure and elastic tensile strength for the porous elastic material in element 2161 instance soil-1 must be positive.

 

[FEA way]

The cam-clay model assumes no stiffness at zero stress so some initial compressive stress has to be defined via *Initial conditions, type=stress.

 

[mojtaba pourgholami]

I defined geostatic stress in model but it doesn't fix

 

[FEA way]

Elastic tensile strength p_t^el is defined via *Porous elastic keyword. It can't be negative but if you omit its value in this keyword then it will be zero. You have to make sure that initial pressure p_0 (defined using *Initial conditions, type=stress) is such that when summed with p_t^el the result is positive.

 

[mojtaba pourgholami]

I can't understand. my model is 3 layer soil with a piled raft foundation. one of my layers is soft clay and I define it by cam-clay and another one with mohr_cloumb .know I deleted all the plasticity properties my model was analyzed then I try all layers with mohr-cloumb but I get this error.
((The plasticity/creep/connector friction algorithm did not converge at 7733 points))
again I used drucker-pruger to define and get this error
((1253 elements are are missing the permeability definition. The elements have been identified in element set ErrElemMissingPermeability))

 

[FEA way]

Could you attach your model's file (.inp or .cae) here ? I would take a look and try to fix these problems. It seems that there are errors in your material definitions.

 

[mojtaba pourgholami]

.cae file of model

 

[mojtaba pourgholami]

and this paper is my reference

 

[mojtaba pourgholami]

did you check?

 

[mojtaba pourgholami]

can anyone help me to fix it?

 

[FEA way]

I had a look at your model and I think that the problem lies deeper than in material definition. I’m not an expert in geomechanics field but, from what I know about this kind of Abaqus simulations, they require special attention when defining initial stress field. In particular, I think that your analysis should be preceded by geostatic step to establish equilibrium. More details about the use of this step (what should be included in its definition) can be found in the documentation chapter "Geostatic stress state" but also in the chapter "Initial conditions —> Defining initial stresses". Please also take a look at the example problem "Consolidation of a triaxial test specimen" (Benchmarks Guide). Reviewing its description and input files should help you fix your analysis which is similar to this example.

 

[mojtaba pourgholami]

I fixed all the problems. but now I have a problem with cam-clay when I use porous elastic I get this error.
The sum of initial pressure and elastic tensile strength for the porous elastic material in element 774 instance soil-1 must be positive.

 

[FEA way]

That's still the same issue as before. Did you add *Geostatic step before all *Static steps, like I suggested in the previous post ? If not then try this approach, it might solve the problem. But read the indicated documentation chapters first because initial stress definition in geotechnical analyses must be done carefully to avoid errors like this one.