Fly Rock Modelling

The Fly Rock Modelling tool provides a method to predict a maximum horizontal distance of fly rock based on model inputs. The resulting boundary may be used to assist with understanding the potential extent of fly rock displacement and determining blast exclusion zones.

To open the Fly Rock Modelling panel, go to the Analysis ribbon > Modelling group > Fly Rock Modelling. The Fly Rock Modelling panel will appear.

Methods

BlastLogic uses kinematic equations from two different methods to calculate fly rock displacement:

  • McKenzie, C.K. (2009). Fly rock range and fragment size prediction. International Society of Explosive Engineers, 35th Annual Conference, Denver, USA.

  • Richards and Moore. (2006). Sourced from the Terrock Supplementary Modelling Report for Kalgoorlie Consolidated Mine.

When using the McKenzie method, the assumed particle shape factor is 1.2. This value is the average value for particle shape distribution and is used to determine the effects of air resistance.

Types of fly rock modelling

There are two types of modelling: 3D and 2D models. Both modelling types use a projectile velocity. The velocity is determined from either the McKenzie or Richards and Moore kinematic methods.

In 3D modelling, the velocity is used to calculate the intercept between the trajectory of the rock and the topographic surface provided. This is repeated for a number of vertical angles until the furthest horizontal distance is found for a given orientation. This is then repeated at various orientations in order to form a boundary around each selected hole. After boundaries around individual holes are created, an overall boundary is generated.

In 2D modelling, it is assumed that the topographic surface is flat and therefore that the maximum trajectory angle is 45 degrees. The velocity is used to determine the intercept with this theoretical surface.

Cratering and face burst are the two components of fly rock that are taken into consideration by the model:

  • Cratering refers to fly rock from the collar of the hole and directly depends on the amount of stemming in the hole. The more stemming, the lower the amount of cratering. Only the top-most explosive deck is considered when the cratering is modelled. The lengths of any inert decks (including air), which are placed above the first explosive deck, are considered to be contributing to the stemming length.

  • Face burst refers to fly rock from a free face (generally a highwall), which is provided by the user as a triangulation. The greater the distance between an explosive deck and the triangulation surface, the lower the amount of face burst.

BlastLogic determines a vector of the closest distance between explosive decks and the free face, and then models this face burst potential in an arc of 180 degrees along the line that is perpendicular to the vector between the deck and the face. Therefore, if a single hole has two different points that are close to the face, only the closest one will be assessed.

Note:  Rifling is not currently considered in any model.

Input parameters

There are eight input parameters:

  1. Factor of safety
    Both 2D and 3D models use a factor of safety when calculating fly rock. However, when it comes to this factor's application, there are some differences between the two models:

    • When calculating the 2D model, the factor of safety is a multiplier applied to the model calculated fly rock horizontal distance.

    • When calculating the 3D model, the factor of safety is a multiplier applied to the initial velocity of the dominant type of fly rock (cratering or face burst).

  2. Blast and data source
    Specify the blast you wish to model in the data explorer or view window. The selection table in the panel will display the selected blast in the Blast column and set the source data to Current in the Source column.

    Optionally, change the data source by selecting the Source drop-down and selecting one of the following sources:

    • Plan
      Select the Plan option to generate a model using only charge plan data. In this case, no loaded or reconciled data is included in the model. This option is in bold to signify that it is a special data type that you can only access in the tie-up editor and fly rock modelling tool.

    • Current
      Select the Current option to generate a model using reconciled data. If there is no reconciled data, BlastLogic will load the plan data instead (but not any loaded data). This option is in bold to signify that it is a special data type and not a snapshot.

    • Reference design snapshot
      The name of the reference design snapshot will appear as an option in the drop-down. For example, the snapshot HP, is in bold to represent that it is the reference design snapshot. Select this option to generate a model using the reference design snapshot data.

    • Other snapshots
      Any other snapshots related to the blast will also appear in the drop-down. Select the name of the desired snapshot to generate a model using that snapshot’s data. These snapshots will not be in bold.

  3. Default rock density
    The McKenzie method uses density to calculate fly rock. If no general average density is provided in the panel, BlastLogic requires the density assigned to each individual hole to calculate fly rock.

  4. K factor
    The Richards and Moore method uses a K factor derived from experimentation.

  5. Rock surface face
    For face burst modelling, a rock face surface is used to calculate the distance between the closest explosive deck and the rock face surface. If no surface is provided, face burst is not considered.

  6. Minimum distance constraint
    The Enable minimum distance constraint checkbox is used to ensure that the fly rock boundary in any direction will be a user-defined minimum distance.

  7. Topographic surface
    For 3D Modelling, topographic surface is used to determine the intercepts for both cratering and face burst modelling. The topographic surface should cover the entire extent of both the blast itself and the potential fly rock zone.

  8. Model fidelity
    Model fidelity can be used to modify the number of sampling points used to generate a result. For example, increasing the fidelity will increase the number of orientations and vertical angles considered by the model. The higher the fidelity, the longer the algorithm will take.

Outputs

BlastLogic creates an overall fly rock boundary using the maximum horizontal distance from each selected hole.

Cratering and face burst are calculated and displayed separately for the 2D model option. Cratering is displayed as a green boundary, while face burst is displayed as a light blue boundary.

The two results are combined when producing a 3D model. If the boundary does not intersect with the topographic surface, the algorithm will use values calculated from the 2D model.

Fly rock boundaries can be saved by clicking the Save polygon button.