# Can we use both deformable blocks and rigid blocks in one model? **URL:** \ **Category:** 3DEC\ **Created:** [February 24, 2025, 8:34am UTC](https://forum.itascainternational.com/t/can-we-use-both-deformable-blocks-and-rigid-blocks-in-one-model/1962 "2025-02-24T08:34:28Z")\ **Posts on this page:** 4\ **Page:** 1
**Author:** ![sanhtra](https://avatars.discourse-cdn.com/v4/letter/s/8797f3/32.png) [@sanhtra](https://forum.itascainternational.com/u/sanhtra)\ **Post date:** [February 24, 2025, 8:34am UTC](https://forum.itascainternational.com/t/can-we-use-both-deformable-blocks-and-rigid-blocks-in-one-model/1962/1 "2025-02-24T08:34:28Z")
Hi Itascans, Can we use both deformable blocks and rigid blocks in the same model (in 3DEC 7.0)? My model includes hard rocks, which can be modeled as rigid blocks and soft soil which must be modeled with deformable block. Because rock elements are in quite small sizes, when using deformable blocks for them, the timestep is too small. Therefore, I consider to use rigid blocks to model them to increase timestep to speed up the calculation. However, when I use rigid blocks for rock elements, I can not mesh the block which is used to model the soft soil. Any suggestion for this issue? Thank you so much. ---
**Author:** ![jmswdmn](https://avatars.discourse-cdn.com/v4/letter/j/51bf81/32.png) [@jmswdmn](https://forum.itascainternational.com/u/jmswdmn)\ **Post date:** [February 24, 2025, 12:36pm UTC](https://forum.itascainternational.com/t/can-we-use-both-deformable-blocks-and-rigid-blocks-in-one-model/1962/2 "2025-02-24T12:36:50Z")
3DEC does not allow for the use of both rigid and deformable blocks within a single model, as documented [here](https://docs.itascacg.com/itasca900/3dec/docproject/source/theory/3dectheory/theory_background.html). “_At present, 3DEC does not allow the use of rigid and deformable blocks in the same problem. The logic applies for both small-displacement and large-displacement relative motion between blocks._” When setting up your model, I would question your justification for wanting to maintain rigid blocks and negate block deformability for your problem in question (indeed it may well be a valid assumption, but block deformability can often be important). I would also question your block/zone size for your problem in question and whether the level of detail is appropriate for the question in mind whilst allowing for computational efficiency. By definition, a model will always be a simplification of reality. P.S. The AI Assistant chatbot answers this question well and references the appropriate link in the documentation far faster than searching through the documentation yourself. [https://geobot.itascasoftware.com/](https://geobot.itascasoftware.com/) ![image](https://canada1.discourse-cdn.com/flex031/uploads/itasca/original/2X/c/c7265cf641a0170e6149a7e702b23a8b02fa2b84.png) ---
**Author:** ![jhazzard](https://avatars.discourse-cdn.com/v4/letter/j/4af34b/32.png) [@jhazzard](https://forum.itascainternational.com/u/jhazzard)\ **Post date:** [February 24, 2025, 7:50pm UTC](https://forum.itascainternational.com/t/can-we-use-both-deformable-blocks-and-rigid-blocks-in-one-model/1962/3 "2025-02-24T19:50:03Z")
Yes, “officially” you can’t have both in the same model. But you can hack it. You need to create the deformable blocks, zone them, and then create the rigid blocks (and not zone them). You may need to give the command “block contact gen-sub” prior to assigning contact properties. In theory this will work, but use at your own risk. ---
**Author:** ![sanhtra](https://avatars.discourse-cdn.com/v4/letter/s/8797f3/32.png) [@sanhtra](https://forum.itascainternational.com/u/sanhtra)\ **Post date:** [March 1, 2025, 1:26pm UTC](https://forum.itascainternational.com/t/can-we-use-both-deformable-blocks-and-rigid-blocks-in-one-model/1962/4 "2025-03-01T13:26:04Z")
Thank you so much for your clear answer.