Help with geostatic analysis
Help with geostatic analysis
(OP)
Hi all,
I am quite new to Abaqus and I'm trying to find the effective stresses on a mass of soil with several layers. I have defined material properties including density, elasticity, Mohr-Coulomb failure and permeability for each layer. I have also applied a gravity force of -9.8 on the geostatic step to the entire system, and I have predefined the total stresses at the top and bottom of each layer. I have defined the groundwater table as a pore pressure boundary condition (with a value of 0), and have defined the initial void ratio of each layer in the predefined fields. For some reason this results in negative pore pressures above the ground water table and negative effective stress values (s22) that are quite larger than they should be. Any ideas on what I missed of if I should be approaching this problem in different steps?
Thank you all in advance!
I am quite new to Abaqus and I'm trying to find the effective stresses on a mass of soil with several layers. I have defined material properties including density, elasticity, Mohr-Coulomb failure and permeability for each layer. I have also applied a gravity force of -9.8 on the geostatic step to the entire system, and I have predefined the total stresses at the top and bottom of each layer. I have defined the groundwater table as a pore pressure boundary condition (with a value of 0), and have defined the initial void ratio of each layer in the predefined fields. For some reason this results in negative pore pressures above the ground water table and negative effective stress values (s22) that are quite larger than they should be. Any ideas on what I missed of if I should be approaching this problem in different steps?
Thank you all in advance!





RE: Help with geostatic analysis
RE: Help with geostatic analysis
RE: Help with geostatic analysis
RE: Help with geostatic analysis
Thanks again!
RE: Help with geostatic analysis
RE: Help with geostatic analysis
So I decided to simplify it even more. I now made it an axisymmetric single layer of soil with no ground water table but the stresses are not negative at the top. I really don't know what I am doing wrong. I attached my file. Could you take a quick look at it? I don't know what else to do. Thank you again!
RE: Help with geostatic analysis
Soil is saturated undrained overconsolidated clay. So note the value of E and v (0.49) I have used. Moreover, I have added Mohr Coulomb plasticity which is the case for my model, but you can do it without this also. I have applied a body force in downward direction and accordingly added *INITIAL CONDITIONS in the KEYWORDS. The direction is extremely important. In my case, upwards in + Z and downwards is - Z. The geostatic step is used with FIXED incrementation. But sometimes one does not get the desired results. In such case, you can use AUTOMATIC incrementation by going into STEP>INCREMENTATION and selecting Automatic option. This is called Geostatic step with Enhanced procedure. Refer section 6.8.2 in Abaqus Manual Part 2 about when and where you can use this.
When you are in visulization module, observe that S33 are pointing downwards (-ive S33) and U3 is also pointing downwards(-ive U3)with very low values 10^-9 m. This implies that the step is successful. I hope this helps you.
RE: Help with geostatic analysis
RE: Help with geostatic analysis