Block dropping in 3DEC

I was simulating a slope with rigid blocks to check the sliding failure.

  1. But even I used different ways to fix all the lower and side boundaries there are still some blocks dropping for long distances as shown. Even I have used different ranges of stiffness’s from normal to high, I don’t know how it can still overlap or it may be a different case. This block dropping is 1st problem.

  2. Does 3DEC have any commands or options like domain detection or cell detection logic in 3DEC?

  3. 2nd problem is sometimes the blocks near the toe fly away. I have used large strain off because I just want to see small deformation.

  4. And can anyone tell me what is the difference between using small and large strain in 3DEC?
    Thank you. Waiting for suggestions. (1.5 KB)

Dear @Akash77skyz,

I’m trying to phrase this as nice as possible: It appears that both you and @Ray (who obviously uses the same model) have a fundamental lack of understanding of very basic principles of geomechanical simulations. This is certainly not your fault, everybody has to start out somewhere, but it makes it quite difficult to help you without basically teaching you a basic course in (in this case) discontinuum mechanics. So I’ll try to answer your questions briefly, but I heavily suggest that you do your due diligence and improve your knowledge on discontinuum methods. The “3DEC modeling” and “3DEC theory and background” sections of the old 3DEC manuals are a great start, even though could be presented more prominently in the new manual.

To your questions:

  1. see 3.

  2. Domain detection is always on in large-strain mode. There are - to my knowledge - no alternative cell mapping algorithms like in UDEC.

  3. It appears that the blocks that are sliding down the upper layer are crashing into the toe and - similar to a water wave - are splashing above it. That actually seems reasonable. Since you don’t have a “base” plate, they would then fall down indefinitely (in large-strain mode).

  4. Again a very basic question that you will find explained in the manual. In every mode, the stresses lead to gridpoint displacements, but in small strain mode these displacements are not added to the gridpoint position (it stays where it is), while in large-strain mode the calculated displacements are added and therefore the blocks actually appear to be moving. Small-strain mode is generally used when the deformations in your model are small compared to the model dimension and meshing, because this makes for faster calculations (no contact logic, geometry changes etc.). Important note: By using the DEFORM box in the plot item, you are essentially “faking” a large-strain model. Maybe this adds to your confusion.


Dear @markus,

Thank you very much for the explanation and your time. Yes we have just started using 3DEC and encountered these problems. Yes we will look more into the manuals and get more knowledge about discontinuum mechanics.

You can actually change the number of cells in the cell space, or the algorithm. See here: block cells command — 3DEC 7.0 documentation (
However, I don’t recommend that you mess with this for such a small model.