Small doubt in gravity loading analysis

Hi all, 

Gravity loading analysis for selected if the soil layers and water table not in a position to produce the equilibrium. In ko procedure it is mentioned that , during that phase don't activate any loading or structures which will provide the loading to the soil. 

My question is does gravity loading has same limitations as in the ko procedure? because i need to model this one (as shown below) and in existing the soil is retained by the circular pile which i need to provide using plate or soil volumes (here i used volume).

Thanks, 

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  • Nitha,

    Here are my thoughts on this.

    The Ko procedure is not a finite element calculation. The procedure calculates the initial vertical stresses based on depth below surface and unite weight of soil. It then calculates the horizontal stresses based on ko parameter. Equilibrium is not calculated. There are no deformations, and structures or loads if turned on, have zero affect. (I'm  thinking structural weights are not included in Ko procedure, you'd have to check to confirm that). 

    I usually always follow a Ko initial stress condition with a ignore undrained behavior Plastic Null step to compute equilibrium. During the Plastic Null step the loads can be applied and equilibrium will be computed and deformations can be zeroed on the next step. I rarely include structural elements in the analysis setting up the initial conditions.

    Gravity loading on the other hand, is a Finite Element equilibrium calculation with weights increasing from from 0.0 to the values entered into Plaxis. Loads and structures can be included in the calculation. The calculation starts from a zero stress condition and the Ko parameters is not used.  

    So to answer your question. Gravity loading does not have the same limitations as the Ko procedure. In my opinion gravity loading is less realistic than a Ko procedure followed by a Plastic Null step. While I rarely use Gravity turn on for soils, I would if I were analyzing a purely linear elastic solution where the results are independent of the stress path.

    Hope this is helpful.

    Martin

    Answer Verified By: Dennis Waterman 

  • Dear Mr. Martin, 

    I checked and for ko procedure structure weight and loads have zero effect and what i interested is here is gravity loading because system is not horizontal as shown above. Problem is if we go with gravity loading we need to reset to zero the displacement and we need to check the stresses whether it follows as same as the ko procedure because gravity loading will produce horizontal forces based on poisson ratio (v).

    Thanks for the reply which help a lot.

    Thanks. 

Reply
  • Dear Mr. Martin, 

    I checked and for ko procedure structure weight and loads have zero effect and what i interested is here is gravity loading because system is not horizontal as shown above. Problem is if we go with gravity loading we need to reset to zero the displacement and we need to check the stresses whether it follows as same as the ko procedure because gravity loading will produce horizontal forces based on poisson ratio (v).

    Thanks for the reply which help a lot.

    Thanks. 

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