FLAC3D Modeling • Problem Solving with FLAC3D

Approach and Project Setup

The modeling of geo-engineering processes involves special considerations, and a design philosophy different from that followed for design with fabricated materials. Analyses and designs for structures and excavations in or on rocks and soils must be achieved with relatively little site-specific data, and an awareness that deformability and strength properties may vary considerably. It is impossible to obtain complete field data at a rock or soil site. For example, information on stresses, properties, and discontinuities can only be partially known, at best.

Since the input data necessary for design predictions are limited, a numerical model in geomechanics should be used primarily to understand the dominant mechanisms affecting the behavior of the system. Once the behavior of the system is understood, it is then appropriate to develop simple calculations for a design process.

This approach is oriented toward geotechnical engineering, in which there is invariably a lack of good data. But in other applications, it may be possible to use FLAC3D directly in design if sufficient data, as well as an understanding of material behavior, are available. The results produced in a FLAC3D analysis will be accurate when the program is supplied with appropriate data.

Modeling on a Spectrum

Modelers should recognize that there is a continuous spectrum of situations, as illustrated below.


Figure 1: Spectrum of modeling situations.

FLAC3D may be used either in a fully predictive mode (right-hand side of the image above) or as a “numerical laboratory” to test ideas (left-hand side). It is the field situation (and budget), rather than the program, that determines the types of use. If enough data of a high quality are available, FLAC3D can give good predictions.

Since most FLAC3D applications will be for situations in which little data are available, the next topic presents a recommended approach for treating a numerical model as if it were a laboratory test. The model should never be considered to be a “black box” that accepts data input at one end and produces a prediction of behavior at the other. The numerical “sample” must be prepared carefully, and several samples tested, to gain an understanding of the problem.

Start a Project

When the initial preparations are complete, the modeling process in FLAC3D starts with the creation of a project. This is a simple but important step. The project “houses” the model and the resources that go into creating it, as well as the outputs that are generated by it.

Create a Project File

To create a new project file, select File --> New Project... from the main menu. This will open a standard dialog that will allow the user to specify the name and folder location of the project file.

Once the file is created, the folder containing the project file will serve as the working directory for the project. All model state (SAV) files will be stored there unless expressly specified by command to be stored elsewhere. In either case, the project will track their existence as part of the project. This allows for a range of facilities, including rapid movement between saved states within the interface, and collection and storage of the commands that comprise each saved state within the State Record pane, which in turn allows for a program undo capability and for creating a bundle file.

The project also saves user interface settings (the layout), model options that have been specified for this project, the state of all program options that are in effect for the project, calculation modes used in the project, and all plots of the model that are created.

The project does not contain saved states, imported files, or data files. These exist as files outside the project. The project does track the use of these files and the locations from which they are drawn.

Project Tools

FLAC3D provides the Project pane for project management. In addition, it provides the Pack facility on the toolbar (Tools ‣ Pack…) for gathering the project file, project source files, and saved state records into a single, easily transmitted/stored file (similar to a compressed archive file). Project files (as part of a bundle) are also the preferred inclusion when sending a technical support request through the Technical Support dialog (Help ‣ Request Technical Support…).