Stockpiles on project sites are most often resting on a flat surface or regular slope, which are easy to properly calculate, but when stockpiles end up resting over a bank it can be difficult to know how to properly model its baseline to get an accurate estimate. For a stockpile over a bank, you will need to use a breakline to correctly model the ground under the stockpile, and we'll show you how you can do that in this article. This article also covers some common mistakes that are often made when trying to calculate a stockpile over a bank and gives you context for a more complex situation of how to properly model the baseline of a trench. 


Overview


Create a Stockpile Over a Bank

To create a stockpile over a bank, you first need to model a surface under the stockpile using a breakline. The image below is a profile of a stockpile (green line) that is located on a bank (black line). Using a breakline, you can model the change of the slope between the bank and the floor of the location. 

Profile view of a properly created baseline under a stockpile resting on a bank.


How to create the proper baseline for a bank under a stockpile:

  1. Draw a Boundary Around the Stockpile: Select the Boundary tool from the HOME tab and start drawing a boundary around the stockpile. Be sure to place vertices on the visible parts of the ground around of the stockpile.
    Drawing a boundary around a stockpile on a bank.
  2. Draw a Polyline Along the Bottom of the Bank: Select the Polyline tool found in the HOME tab and draw a line parallel with the lowest part of the bank. It can be helpful to use the Arc version of the Polyline tool, switch to 2D mode, and have the line follow the curve of the ridge at the top of the bank as closely as possible. Be sure to snap each end of the line to the drawn boundary.
    Draw a breakline along the bottom of the bank.
  3. Adjust the Polyline to Represent the Elevation Between the Bank and the Floor as a Breakline: The polyline is created on top of the stockpile, and you still need to convert it to match the break along the bottom of the bank under the stockpile. Switch back to 3D mode to get a better view of the polyline on the stockpile. Make sure your polyline is selected, then go to the TOOLS tab and select Edit Vertex. Enable Interpolate Z of the Edit Vertex Mode to drop the polyline's middle vertices to linearly interpolate between the two end vertices and create the breakline at the bottom of the bank.
    Interpolate the breakline under the stockpile.
  4. View the Created Breakline Under the Stockpile: You can enable the Transparent Lens from the ANALYSIS tab to get a better understanding of what the breakline looks like under the pile. This is the best estimation you can get for what the breakline would be like under the pile.
    Turn on the Transparency Lens to see the breakline through the stockpile.
  5. Generate the Surface Under the Stockpile: Now with the breakline in place, select the boundary you've drawn around your stockpile and select Triangulate Within, found in the HOME tab. This will create a TIN (surface) that includes the breakline under the stockpile.
    Create a traingulated surface under the stockpile including the breakline along the bottom of the bank.
  6. Modify the Terrain to View the Slope at Ground Level: With the TIN selected, go to the TOOLS tab and select Modify Terrain to get an idea of what the ground looks like without the stockpile.
    Modify the Terrain to the surface underneath the stockpile and move it to the appropriate layer.
  7. View the DSM without the Orthophoto: You can also turn the orthophoto off to get a better feeling of how the terrain is shaped under the stockpile. Enable and disable the modified terrain item to clearly see what it looks like without the stockpile.
    View the DSM without the Orthophoto and toggle the terrain modifier on and off.
  8. You can now create your stockpile. You can now use the surface item to create your stockpile. Just be sure to disable the modified terrain (if you wanted to clearly see what the surface looks like under the stockpile), select your surface, and create the stockpile.
    Create a stockpile from the surface with a breakline.


Understanding Breaklines Under the Stockpile

Creating stockpiles over different slopes and gradients on the terrain is a bit abstract and difficult to imagine how it is done if there is a bank, ditch, or trench. But like a magic trick, it is very simple once you understand the concept. As explained in this article, all you need to do is draw a boundary around the stockpile and draw a breakline for each of the slope changes under the stockpile. 


Common mistakes when calculating a stockpile over a bank. It is a common misunderstanding to draw a boundary around the stockpile without drawing a breakline and assume the computer can visualize the ground under the stockpile. Virtual Surveyor uses smart tools like the Flat, Flat Minimum, or 3D Surface options to quickly generate a surface under a stockpile. As shown in the illustration below, a boundary combined with a Flat or Flat Minimum results in the cyan profile line, and the 3D Surface results in the magenta profile line. Neither are accurate over a bank because the computer has no way of visualizing slope changes under a stockpile without human help, which is why you need to draw the breakline inside the boundary and manually create a surface to show the computer what the baseline looks like under the pile (black profile line).

Profile view comparing common mistakes with the accurate profile of a bank when creating the baseline under a stockpile.


Stockpile Over a Trench. You can use the same concept and technique for creating a stockpile over a bank to create a stockpile over a trench. It is a bit more complicated, but only in that you need to create four breaklines under the stockpile to model the top and bottom lines of the trench to make the appropriate surface under the stockpile. Using the same method as shown in this article for drawing the proper baseline under a bank, you draw a boundary around the stockpile, then draw breaklines at each of the slope changes under the stockpile. This same method applies to any stockpile that rests on top of a ditch, bank, trench, etc., you just need a breakline for every slope change under the stockpile to properly model the ground level. You might also need to use other Edit Vertex tools to properly adjust the vertex elevation.
Profile view of a stockpile over a trench.