I have been working on a pile-soil interaction model in ABAQUS where the soil is consisted of 6 layers (1 Clay + 5 Sand layers or 1 Sand+ 5 Clay layers). My problems are as follows:

a. When I made the elastic input for all the layers separately, the analysis worked perfectly. Then I started inputting the plastic properties by applying it in one layer at once (First in layer-1, then layer-1+2, etc.). When the plastic properties of layer-1 (Clay) is assigned (rest remained elastic, sand), the analysis was completed as well. But when I entered plastic values for 2nd layer, the model started showing error “Too many attempts made for this increment”, and in the message it kept showing “The plasticity/creep/connector friction algorithm did not converge at X points.”

b. I deleted all the soil sections, and assigned the elastic and plastic values of 2nd layer to the whole soil model. The analysis was stopped showing same message.

c. I made another model with 2 soil layers and assigned both the elastic and plastic values of layer-5 (Dense Sand). That model worked perfectly. But when I entered the same values for 6 layer soil model, the analysis stopped.

I am using M-C plasticity. I am completely clueless about this one. I would be grateful if anybody can suggest some solutions to these problems, I am feeling helpless.