To model anchored cable bolts (passive bolts) in FLAC 2D 8.1 software, you can follow these steps:

1. Launch the FLAC 2D software and create a new project.

2. Define the material properties for the surrounding rock and any support elements like steel sets or shotcrete that will be used.

3. Set up the geometry of your tunnel by defining its shape, size, and location within the FLAC 2D grid.

4. Define the mechanical properties of the rock mass, such as elastic modulus and Poisson's ratio.

5. Specify the excavation sequence by creating stages. Each stage represents a particular step in tunnel construction, such as initial excavation, installation of passive bolts, etc.

6. Within each stage, define boundary conditions like fixed supports or prescribed displacements.

7. To model anchored cable bolts (passive bolts), you can use beam elements to represent them. Add beam elements to your model at appropriate locations along the tunnel walls where you want to install passive bolts.

8. Assign material properties to the beam elements based on the characteristics of the passive bolts being used (e.g., Young's modulus).

9. Apply pretension to the beam elements representing the passive bolts using appropriate initial axial forces in each bolt element.

10. Define contact conditions between various components of your model, such as rock-rock contact or bolt-rock contact.

11. Run simulations to analyze the behavior of your tunnel system under different loading conditions.

Remember that this is a basic outline of how to model anchored cable bolts in FLAC 2D software, and you may need to consult the software documentation or seek expert advice for more detailed guidance specific to your project requirements.

Note: Excavating a tunnel involves several steps beyond just modeling; it includes meshing, defining boundaries, assigning properties, applying loads/conditions, analyzing results, etc., which cannot be covered fully here due to space limitations. It is recommended to refer to the FLAC 2D software documentation or seek professional guidance for a detailed understanding of the modeling process.