Help needed: Replicating PFC 2D example in PFC3D

PFC
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1

Hi everyone,

I was trying to replicate the direct shear box example given in this in PFC3D. According to the manual, the example is for PFC2D, but the same procedure would work in PFC3D. While I was able to recreate the general mechanism of the direct shear test in PFC3D, I am having some trouble applying the normal load on the top of the specimen before shearing. The specimen tends to dilate, and the balls appear to spill over when I apply the servo load to the top wall, just like in the 2D example (screenshot attached).

screenshot1
screenshot11920×1112 95 KB

I thought the most likely issue was the low porosity value of 0.17 in the 2D example, which caused it to generate a close packing with significant overlaps. I increased the porosity to 0.35, and while the spillover is not as apparent, there still seems to be an increase in volume.

screenshot2
screenshot23800×2200 224 KB

I also tried to increase the loading magnitude, which caused the walls to disappear. I therefore want some suggestions/tips on how to solve this issue. Here is my data file:
dss_attempt2.dat (2.8 KB)

Thank you,
Prabhat

2

Hello @paudyalp11
You will most likely need to change the gain-factor, gain-update or velocity-max in the wall servo command in order to maintain a constant force on the wall. The initial packing of the balls will determine if the sample dilates or contract. My guess is that you have a very tight initial packing and thus the sample dilates upon shearing.

3

Hi, @dblanksma, I was able to solve this issue by relaxing the physics of the balls a bit by reducing their elastic modulus. Still, I will look into changing the parameters that you mentioned. Thanks for the help.

4

Hello,

I have established a 3D direct shear test using PFC3d and it worked very well. However, i got the Peak shear test After a large displacement. While in experimental test the whole displacement test is 8 mm and the Peak reached quickly. I doubt in consolidation time. Could any one help me with this issue.

Djaafri Djamel