FLAC3D is a numerical modeling code for advanced geotechnical analysis of soil, rock, and structural support in three dimensions.

FLAC3D is used in analysis, testing, and design by geotechnical, civil, and mining engineers. It is designed to accommodate any kind of geotechnical engineering project where continuum analysis is necessary. FLAC3D utilizes an explicit finite difference formulation that can model complex behaviors not readily suited to FEM codes, such as: problems that consist of several stages, large displacements and strains, non-linear material behavior and unstable systems (even cases of yield/failure over large areas, or total collapse).

Dynamic Options: The dynamic analysis option permits three-dimensional, fully dynamic analysis with FLAC3D. User-specified acceleration, velocity, or stress waves can be input directly to the model either as an exterior boundary condition or an interior excitation to the model. FLAC3D contains absorbing and free-field boundary conditions to simulate the effect of an infinite elastic medium surrounding the model

This option can be coupled to the structural element model, thus permitting analysis of soil-structure interaction brought about by ground shaking. The dynamic feature can also be coupled to the groundwater flow model. This allows, for example, analyses involving time-dependent pore pressure change associated with liquefaction. The dynamic model can likewise be coupled to the optional thermal model in order to calculate the combined effect of thermal and dynamic loading. The dynamic option extends FLAC3D's analysis capability to a wide range of dynamic problems in disciplines such as earthquake engineering, seismology, and mine rockbursts.

Creep Options: This option can be used to simulate the behavior of materials that exhibit creep (i.e., time-dependent material behavior). There are eleven available material models (Maxwell model, Burgers model, Power model, WIPP model, Burgers-Mohr model, Power-Mohr model, Power-Ubiquitous model, WIPP-Drucker model, Soft-Soil-Creep model, WIPP-Salt model and Columnar-Basalt (COMBA) Mode) in FLAC3D that simulate viscoelastic and viscoplastic (creep) behavior. 

FLAC3D grid can be configured for both a creep calculation and a dynamic calculation. However, both models are generally not used simultaneously because of the widely different timesteps.

In addition, it is also possible for users to write their own creep constitutive models using the C++ UDM option.

Thermal Options: The thermal option of FLAC3D incorporates both conduction and advection models. The conduction models allow simulation of transient heat conduction in materials, and the development of thermally induced displacements and stresses. The advection model takes the transport of heat by convection into account; it can simulate temperature-dependent fluid density and thermal advection in the fluid.

User-Defined Constitutive Models: You may create your own user-defined constitutive model (UDM) for use in FLAC3D. The model must be written in C++ and compiled as a DLL file, and can be loaded whenever needed or loaded automatically if placed in the “exe64\plugins\models” folder. The main function of the constitutive model is to return new stresses, given strain increments.


  • Interactively create models from CAD files (DXF, STL), sketching, or images
  • Automatic structured and unstructured mesh generation
  • Skinning to automatically identify model boundaries to set boundary conditions
  • Interactively assign groups, constitutive models, and properties/distributions
  • Extrude linearly and along curves
  • Skinning to automatically identify model boundaries to set boundary conditions
  • Interactively assign groups, constitutive models, and properties/distributions
  • Built-in database to save/import/export material properties
  • Automatic stress initialization
  • Intuitive commands are easy to learn
  • Most UI interactions are automatically translated into commands, which can be saved to a datafile and re-used
  • Built-in help / command auto-complete
  • Advanced built-in text editor makes creating and running models simple
  • Large-strain simulations to capture the full extent of model deformation
  • Includes 27 built-in constitutive models
  • Non-linear deformable ground support elastic and elastoplastic structures
  • Advanced plotting tools to understand your model results and for working with hundreds of plots on real projects 
  • FISH, Itasca’s scripting language, provides unparalleled control over, and customization of, the model
  • Built-in Python 3.10 scripting includes SciPy for plotting, NumPy for computing, and Pyside for UI customization
  • Statistical generation tools for Discrete Fracture Networks (DFNs)
  • Access and modify almost all variables (including “EXTRA” variables for zones, piles, gridpoints, etc.) via FISH/Python
  • Import and export any ASCII data format
  • UDMs can be written in C++ using Visual Studio template
  • Automatic factor of safety analysis (shear strength reduction method)
  • Back-analyze failure and calibrate forward-prediction
  • Parametric studies via FISH or Python
  • Service limit state (SLS) and ultimate limit states (ULS) based on displacements
  • Automatic zone relaxation simulates gradual excavation for construction sequencing
  • Simulate material damage and failure
  • Effective stress using conventional or complex pore pressure distributions
  • Fluid flow, seepage, and consolidation
  • Coupled ground-structure interaction (beams, cables, piles, shells, geotextiles, liners)
  • Simulate discontinuities (faults, joints, bedding planes, and construction boundaries) using interfaces; capture yielding or failure, shear displacements, opening, and closure along them
  • Static and dynamic liquefaction