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3DEC Version 5 can build and use Discrete Fracture Networks (DFNs) to create joints in 3DEC models. But, because all blocks in 3DEC must be convex, cuts must split blocks entirely, even if the fracture only passes partway through the block. This problem is resolved by assigning properties to the subcontacts lying within the fracture that differ from those lying outside of the fracture — which is easily accomplished with the change dfn command.

A problem with this approach is the plotting of joint materials. Joint plots in 3DEC color joints by contact material number. But, with DFNs, it is possible to have some subcontacts with different material numbers than those of the host contact. The figure below shows an example in which the contact centroid lies outside of the DFN fracture so it is assigned the material number corresponding to outside of the fracture (in this case material 3). When you plot the joints and color by material number, it appears that the change dfn command didn’t work!

To see what is really happening, you can create user-defined scalars corresponding to each subcontact and color them according to the subcontact material number (see the FISH function included with the example below). This shows that the change dfn command did indeed work and that the subcontacts have been assigned the correct material number (2 in this case). You can also convince yourself that it is behaving correctly by contouring the joint properties.