Blocks, Joints, and Zones

The fundamental component of all 3DEC models is the block. Every 3DEC model is made up of an assembly of blocks. The blocks interact at points of contact. 3DEC can be used to simulate a loose assembly of blocks such as an aggregate or a fill material, however it is more commonly used to model a jointed or faulted rock mass. The contacts between the blocks can then be considered as joints, faults, cracks or bedding planes. The blocks themselves can be rigid or deformable. To make a block deformable, it must be divided into zones - usually tetrahedra. The main components of a typical 3DEC model are therefore:

• Blocks

• Joints (contacts)

• Zones

A 3DEC model can be created in two ways: (1) by splitting a single block into separate polyhedra; and (2) by creating separate blocks and joining them together. Methods for creating single blocks are described in the next section. The section Generating Block Assemblies describes how to build a model from many separate blocks. How to cut blocks to create joints or faults is described in Cutting Blocks. Finally, methods for zoning blocks to make them deformable are described in Zoning 3DEC Blocks.

3DEC models may also include flow planes to simulate fluid flow through joints, or structural elements to model ground support. These components are described in the 3DEC Theory and Backround section.

One of the main challenge with building 3DEC models is deciding on the amount of detail to be included. The first rule is keep the model simple. Usually, a numerical model is being developed because the real-life situation is too complex to understand. There is a tendency to attempt to include every possible feature in a numerical model. This results in a 3DEC model that is also too complex to understand. The goal of the modeler should be to understand the mechanisms, properties and parameters that determine the model’s behavior. The time required to calculate a solution also increases with increasing complexity. Therefore, it is to the modeler’s advantage to start with a model that only includes the minimum of features. The complexity of the model can then be increased by adding features one at a time and noting the effect. By using this approach, the modeler has the best chance of gaining understanding of the parameters that are critical to the real-life situation.

The following sections provide techniques and advice for building 3DEC models.