# Problem Solving with FLAC3D

This section provides guidance in the use of FLAC3D in problem solving for static mechanical analysis.[1] It does so by breaking the modeling process down to a sequence from project start to project completion, as follows.

- Project Planning and Setup
- Grid Generation
- Identifying Regions of the Model
- Working with Geometric Data
- Choice of Constitutive Model
- Material Properties
- Boundary Conditions
- Initial Conditions
- Stepping To Equilibrium
- Loading And Sequential Modeling
- Structural Support
- Interfaces
- Tips and Advice
- Interpretation Of Results
- Project Completion

Each of these modeling aspects is discussed in detail. The user who is familiar with the two-dimensional program FLAC will find that the modeling approach is very similar in FLAC3D. The major difference is the procedure for grid generation. We recommend that Grid Generation be studied carefully, and that the user grasps the techniques for grid generation presented there before creating their own model grids.

You will note that FISH programs are used in this section to assist with model generation and problem solving. If you have not used the FISH language before, we recommend that you first read Tutorial: Working with FISH.

The philosophy of modeling in the field of geomechanics was presented earlier in the topics discussed in the section Modeling Methodology. The novice modeler may wish to review that section first. The methodology of modeling in geomechanics can be significantly different from that of other engineering fields, such as structural engineering. It is important to keep this in mind when performing any geomechanics analysis.

Section Outline

- Approach and Project Setup
- Grid Generation
- Identifying Regions of the Model
- Working with Geometric Data
- Choice of Constitutive Model
- Material Properties
- Boundary Conditions
- Initial Conditions
- Uniform Stresses — No Gravity
- Stresses with Gradients — Uniform Material
- Stresses with Gradients — Nonuniform Material
- Stress Initialization in a Nonuniform Material
- Compaction within a Nonuniform Grid
- Initial Stresses following a Model Change
- Stress and Pore-Pressure Initialization with a Phreatic Surface
- Initialization of Velocities

- Reaching Equilibrium
- Loading and Sequential Modeling
- Structural Support
- Interfaces
- Tips and Advice
- 1. Check Model Runtime
- 2. Effects on Runtime
- 3. Considerations for Zoning Density
- 4. Automatic Detection of an Equilibrium State
- 5. Considerations for Selecting Damping
- 6. Check Model Response
- 7. Initializing Variables
- 8. Minimizing Transient Effects on Static Analysis
- 9. Changing Material Models
- 10. Running Problems with In-Situ Field Stresses and Gravity
- 11. Determining Collapse Loads
- 12. Determining Factor of Safety
- 13. Use Bulk and Shear Moduli
- FLAC3D Runtime Benchmark

- Interpretation
- Project Completion
- References

Endnotes

[1] | Problem solving for coupled mechanical-groundwater analysis is discussed in Fluid-Mechanical Interaction, and for coupled mechanical-thermal analysis in Thermal Analysis. Problem solving for dynamic analysis is discussed in Dynamic Analysis. The fluid formulation is a standard feature of FLAC3D; thermal and dynamic analysis are available separately as FLAC3D Options. |

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