Validation of tension pile

Question

I am trying to validate a small-scale rough tension pile embedded in sand using PLAXIS 3D. I am using a volume pile with the linear elastic constitutive model for concrete and sand with MC constitutive model. The volume pile was modeled with an interface by providing an R inter value of 0.75. The attached image is the comparison of the uplift load-deformation curve of the FE model and experimental model. I have also modeled a similar tension pile using field data from literature resulting in a similar curve with the FE model giving a linear response. I have used different meshes and different constitutive models also but the response of the FE model remains somewhat the same. 
 Is the numerical model considered validated when we are getting such a response? Is there anything I can do to improve the model further?

Dennis Waterman · Answer

Dear Jerin, 
 I had hope adding the elasto-plastic behaviour to the soil would be sufficient, but I see from your graph that it isn't. Hence, the solution is in the modelling of the soil-pile interaction. You have now used the simple method of an Rinter value in the interface, but this may be too simplified. Since the soil around the pile has been remoulded due to the pile installation the behaviour may be more complicated than just reduced strength and stiffness with the same factor. Not to mention that also the stress state around the pile was altered by the installation. Maybe the interface requires its own material set with manually reduced stiffness and strength parameters. So my suggestion would be to give the interface its own material set. Initially just a copy of the material set used for sand and then try to reduce some of the parameters. Since the interaction is mostly shearing and it seems that the pile behaviour is too stiff in the beginning, I would start to reduce E50ref to see what improvement that brings. 
 With kind regards, 
 Dennis Waterman

Dennis Waterman · Answer

Dear Jerin, 
 You're currently doing a back calculation, which is not a prediction. So if you find a consistent method that gives good results on multiple back calculations under well defined conditions then that method may be used for a prediction as well under the same conditions. 
 With kind regards, 
 Dennis Waterman

Validation of tension pile

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