Features in FLAC/Slope


  • Now freeware provided at no cost and with no time or size restrictions
  • No CPU limits
  • Simplified user interface and workflow
  • Specifically designed to perform multiple analyses and parametric studies for slope stability projects
  • Failure mode develops naturally – no need to specify a slip surface or failure mechanism
  • Predict multiple, interacting failure mechanisms (failures can propagate)
  • Structural interaction (e.g., rock bolt, soil nail, or geogrid) is modeled realistically as fully coupled deforming elements, not simply as LEM equivalent forces
  • Extensive solution controls and options
  • Multi-threaded mechanical calculations
  • Built-in PDF manual and example files
Cable structural elements can be used to represent soil nails, rock bolts, or geosynthetic sheets. Axial forces and the surface failure location are plotted. Slope FoS is 0.92 without reinforcement and 1.23 for geogrids with a bond cohesion of 10 kN/m.

Grid and Geometry

  • Wizards for generating slope, bench, dam, and general surface grids
  • Automatic and customizable meshing tools

Materials and Models

  • Mohr-Coulomb, Hoek-Brown, and Ubiquitous joint materials are available
  • Built-in materials library includes gravel, sand, silt, clay, and rock properties
  • Add, save, edit, and import/export your own material properties with the library
  • Easily define geotechnical layers
FLAC/Slope model with a thin weak layer. A study of the ratio of cohesive strength (weak layer vs. surrounding soil) of 1.0, 0.6 (shown), and 0.2 showed FoS of 1.45, 1.37, and 0.54. For the 0.2 case the failure was confined to the thin weak layer only.

Boundaries and Conditions

  • Automatic boundary conditions
  • Apply stresses (Sxx, Sxy, Syy, normal, shear, and pressure) and forces (Fx, Fy)
  • Cable structural support elements can be added as geosynthetic sheets or spaced (out-of-plane) ground reinforcement to simulate ground-structure interaction.
  • Easily add a water table to include pore pressures for effective stress calculations
  • Add a Mohr-Coulomb interface to represent a weak plane for faults, joints, or artificial boundaries
  • User-defined gravity settings


  • Plane strain or axisymmetric analysis
  • Automatic FoS calculations using the shear strength reduction (SSR) method
  • Structural support elements, materials, and interface properties can be included or excluded as part of the FoS calculation
  • Exclude model regions from the FoS calculation to capture the global failure
  • Pseudostatic analysis with constant horizontal and/or vertical accelerations to represent an earthquake
  • FLAC/Slope model records can be saved and imported into FLAC for additional analysis


  • Available plot items:
    • Materials
    • Shear strain rate contouring (failure surface location)
    • Velocity vectors (failure mode)
    • Pore pressure contouring
    • Model boundary or mesh
    • Water table
    • Applied conditions
    • Plasticity indicators (yielding/failure)
    • Ubiquitous joint angles
    • Ground reinforcement elements and axial forces
    • Calculated FoS (in legend)
  • Export model plots as bitmap, postscript, and DXF formats
  • Generate an HTML report with material, interface, and structural element property tables and solution table
  • Optionally show resources to:
    • View all of the background FLAC commands generated as you create and run models
    • Query the model using FLAC commands
  • Compare runs using different parameters, and even compare results from different projects
FLAC/Slope model of dam showing the model view (top); water table, pore pressures, and applied forces to represent the water head above the dam (middle); and the resulting maximum shear strain rates and velocity vectors with a FoS of 2.45 calculated.

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