New in 7.0


FLAC is faster and it has a new user-interface. The underlying calculation engine remains robust and reliable, but the user-experience is completely altered and enhanced.

To get an idea, the list of new or improved features provided below gives an overview (though it is not exhaustive; a complete list of changes to the program will be available in the documentation supplied with the demo version).

The list of new or improved features provided below gives an overview:

New or Improved Features

Improved GUI

The structure and layout of the graphical interface has been modified and enhanced to improve user control of model creation and operation. Manipulation of the model and plot views by click and drag mouse operations is much easier in Version 7.

Screen shot of the new FLAC 7.0 GUI; click here or on the image to enlarge in a separate window.

New Grid Generation Tools

Version 7 contains two new grid generation tools that greatly facilitate model creation. The Sketch tool and the Geometry Builder tool make model creation easier to perform and can readily produce regular quadrilateral zoning to provide good accuracy in the solution calculation.

The user can sketch the problem boundaries (both external and internal) and/or import a CAD drawing in the Sketch tool. The sketch can then be used in one of three ways to create the FLAC grid.

  1. The sketch can be a background image for a user-defined grid or a grid library template. The grid can then be snapped to fit both the external and internal boundaries of the sketch.
  2. The sketch can be exported from the Sketch tool as a series of tables. The tables can then be used with the GEN TABLE command to fit the grid to the geometry.
  3. The sketch geometry can be split into quadrilateral blocks in the Geometry Builder tool. The Virtual/Edit tool is then used to create and modify the zoning within the blocks.

Lined Twin Tunnels from Sketch to FLAC Grid — Step 1 Sketch Mode

Lined Twin Tunnels from Sketch to FLAC Grid — Step 2 Geometry Builder Mode

Lined Twin Tunnels from Sketch to FLAC Grid — Step 3 Virtual/Edit Mode

Lined Twin Tunnels from Sketch to FLAC Grid — Step 4 FLAC Grid

Multithreaded Calculation

The calculation of the equations of motion and constitutive relations are multithreaded in FLAC 7.0 to take advantage of multiple core processors of the latest personal computers. FLAC simulations have run approximately three times faster with Version 7 operating on a 2.67 GHz Intel core i7 multi-processor computer. Note that speed increase will vary from computer to computer, based on factors including number of processors, processor architecture, and available RAM. The multithreading at present does not operate if a FISH constitutive model is assigned in the model.

Speed increase on a 2.67 GHz Intel core i7 multi-processor computer


The factor-of-safety calculation in FLAC 7 includes new options to help speed the calculation. An optional bracket can be specified by the user to limit the range for the strength reduction calculations. It is also possible to test if a specified factor is above or below the actual factor. A new Factor-Of Safety volume is provided with the FLAC 7 Manual that contains more guidelines and working examples of safety factor calculations. Different approaches to using the strength reduction method are also described, including the calculation of multiple local minimum stability states within one FLAC run.

Factor-of-Safety Contours

New Constitutive Models

Modified Hoek-Brown Model

A modified version of the Hoek-Brown model, called MHOEK, is characterized by simple plastic flow rule choices given in terms of dilation angle. A tensile yield criterion is also included. The modified Hoek-Brown model can also be run with the strength reduction method to calculate safety factor using the SOLVE fos command.

Factor-of-safety result for rock slope failure in Hoek-Brown material

CHSoil Model

The specific features of the Chsoil model include a built-in friction hardening law that uses hyperbolic model parameters as direct input, a frictional Mohr-Coulomb shear envelope, and two built-in dilation laws (one is based on Rowe stress dilatancy theory and the other is a user-defined dilation hardening/softening law). Chsoil may be used as an alternative to the nonlinear elastic Duncan and Chang model and does not have the drawbacks of that model.

Comparison of laboratory and numerical results for triaxial tests at three different mean stress levels

Liner (M-P diagram)

Improvements to the structural element liner logic include:

  • Customized P-M diagram may be input in a lookup table.
  • Crack is permitted to develop when simulating an unreinforced liner.
  • A residual compressive strength is added as a new liner property and is applied after the peak strength has been reached.

Moment - Thrust Diagram – include residual compressive and tensile strengths

Moment - Thrust Diagram – with zero tensile strength and crack depth ratio = 0.33

Additional Features

  • Improved CYSOIL model. COHESION and TENSION are considered; softening/hardening tables may be specified for cohesion and tension in lookup tables, CTABLE and TTABLE.
  • Added ATTACH REMOVE command to allow removing grid-points from attach list.
  • Added new keywords 'nd_ex1' and 'nd_ex2' to plot extra nodal offsets; and new keywords 'el_ex1' and 'el_ex2' to plot extra element offsets.