- SHOTPlus™ Variant:
Underground
- Version:
> 2.11.1
- KBA Summary:
This article summarises the Powder Factor Ring View in SHOTPlus™ Underground and how to customise the heatmap.
Introduction
SHOTPlus™ Underground has a view where users can see the powder factor distribution across a ring and how powder factors dynamically adjust with changes to hole design.
Understanding Powder Factor
Powder factor is a measure of how many mass units of explosives are enacting upon a unit of rock volume or rock mass. This is typically calculated using the following formula:
where:
C is total charge weight of hole in kilograms
B is the hole burden in metres
S is the hole spacing in metres
L is the hole length in metres
ρ is the density of the rock mass in kilograms per m³ (used when want the PF units to be in kg/t).
However, this calculation has some limitations when it comes to calculating and visualising how powder factor may vary in complex hole geometries. The model above is useful in instances where:
holes are spaced across a blast uniformly, and
charges are evenly distributed across holes.
Most underground blast designs will require a more complex solution for determining powder factor and understanding distribution of explosives between holes.
Methodology
SHOTPlus™ Underground aims to overcome the challenges outlined above by utilising finite element mathematics to “distribute” explosives across the rock mass between holes. Using a customised relaxation model, SHOTPlus™ Underground re-distributes the explosive charge from it’s insitu position in the holes across the cells representing the rock mass. This allows users to model the expected behaviour of the complex geometry, i.e. where holes and/or charges are in close proximity to each other there is a higher concentration of explosive mass. Where the holes and/or charges are further apart, the charges act more independently.
Information
SHOTPlus™ Underground runs 2,000 iterations of the model before stopping the calculation. After this number of iterations, the distribution has reached a stable state, before the algorithm distributes mass outside the bounds of expected behaviour. Users will be able to see these iterations occurring, as colours shift across the heat map when opening the view or switching between rings.
This methodology will allow users to model powder factor distribution across a ring consistently for simple and complex underground blast designs as shown in the following images.
Blast Limits
Due to the nature of the algorithm used by SHOTPlus™ Underground to model the powder factor, a limit needs to be defined for where the zone of influence of a blast hole ends. The user will be able to select from three options to create a limiting boundary around the holes:
- Tight: uses a convex hull around the hole toe and collar to create a boundary.
- Radius: uses a user-defined value to build a cylinder around the hole to limit the algorithm.
- Loose: uses a combination of the convex hull and user-defined radius value to create a limiting boundary.
Information: Single Hole Behaviour
If a ring contains only one hole, the “tight” blast limit will notionally behave the same way as the “radius” or “loose” models. Due to the different methods of calculations, some minor colour differences in the powder factor heat map and average powder factor may be seen.
Information: Result Variability
Results in the Powder Factor Ring View may differ based on the selected product and its density type. When using variable gassing products or density modes such as UGCalculated, the heatmap reflects density changes along the hole. This means calculations and visual outputs can vary depending on product configuration and density behaviour.
Using the Powder Factor Ring View
In order to use the ring powder factor view, the following items must be addressed:
- Holes should be charged with bulk explosives, and
- Ring view must be activated.
To open the Powder Factor View, navigate to View > Ring powder factor.
A window called “Powder factor view” will open. This window can be moved around your screen(s), and left open while interacting with SHOTPlus™ Underground. As you adjust your view by moving through the rings in Ring View, or make adjustments to the design for holes, the Ring Powder factor view will recalculate and update the heat map.
When in Ring View and the Ring powder factor view is open, users will see this window.
- Ring powder factor heatmap: This diagram displays the outputs of the powder factor modelling, using a colour legend to categorise outputs. The aspect ratio of the heat map will match the ring being displayed.
- Legend: The legend shows the powder factor bins and associated colours for the heat map.
- Ring burden: The user is able to specify (to two decimal places) the ring burden used in the powder factor calculation for the displayed ring. A default ring burden can be specified in the “Powder factor calculation” settings. This burden is also used in the average powder factor calculation.
- Rock density: This is the defined rock density, which can be defined in the “Powder factor calculation” settings.
- Total explosives: this is total bulk explosive mass in the charge design for the ring.
- Bounds area: the cross-section area as defined by the blast limit, used in the average powder factor calculation.
-
Ave. powder factor: is the average powder factor for the selected ring, using the following values:
- Total explosives
- Ring burden
- Bounds area
- Rock density (if using explosives mass per rock mass as units).
- Settings: this button will open the “Powder factor calculation” settings dialog box.
- Lock bins: this button will enable or disable locking the legend bins. This allows users to use the same powder factor bins across multiple rings, so that it easier to make a direct comparison of powder factor. If this is disabled, the bins will automatically reconfigure to suit the distribution of powder factor in the ring.
- Ring name: The ring name for the visible ring will be displayed here.
Powder Factor Calculation Settings
Users can open the Powder Factor Calculations settings via:
- The Settings button on the "Powder factor view", or
- In the Powder Factor Calculations menu in Edit > Blast Properties.
- Bins: In this section, users can enable “Auto” or “Manual” mode for the binning of powder factor values. When using “Auto” mode, the application will determine how many bins to use for the heat map and they will recalculate every time the view is changed. When using “Manual” mode, the user can specify the minimum and maximum values and the bin increments. “Manual” mode automatically locks the bins and uses this configuration for every ring.
- Blast limits: the user is able to specify which blast limit method they would like to use. When “Radius” or “Loose” is selected, the user will be able to specify a radius.
- Rock density: Users are able to switch powder factor units to explosive mass per rock mass (i.e. kg/t in metric) by selecting the check box. Users can specify the rock density to use for this conversion in this section.
- Default ring burden: This is the default ring burden applied to new files. This can be adjusted via Program Settings when all files are closed. A ring burden value can be set for a specific ring by adjusting the ring burden value on the Ring Powder Factor view dialog.
- Click OK to save and apply the changes.