Dirt management on construction sites is a challenge. Thanks to drone surveys it's now easier to get better insights of your earthworks projects. However the drone data has to be efficiently analyzed to be useful for project monitoring. This article will show you a step by step guide to teach you how to provide a relevant Cut/Fill analysis.
Drone data coming from construction sites are commonly full of machines (bulldozers, excavators, dump trucks...) and materials. You don't want to include these objects into your earthworks calculations. To clean your terrain, you can use the one-click Remove Object tool or the more robust Replace Terrain tool. To help you detect objects that need to be removed, you may also use the Slope Steepness Terrain Lens. This must be done for each drone survey.
Cut/Fill analysis between 2 terrain states
Let's compare a drone survey with another drone survey obtained earlier to analyse the work that was done between those two dates.
Terrain state management
To deal with multiple drone surveys you need to use the Terrain State tool. Create a Terrain State for each date the site has been flown. Each drone survey data package (DSM and orthophoto) must be imported in the dedicated Terrain State. Switch from a terrain state to another and make sure both are fully cleaned. Then, stay on the least recent.
Before going further you need a boundary that defines the limits of the construction site or the area of interest. You can use the Boundary tool available in the HOME tab to draw that item or import a DXF file that contains a polyline. Have a look to this article if you want to update an existing boundary.
By selecting the boundary you can access Volumes tools group in the TOOLS tab. Select the reference terrain state (most recent) in the box and click on Volume Difference button to create the Cut/Fill map. Cut areas appear in warm colors (yellow to red) and fill areas appear in cool colors (cyan to blue). Cut/Fill values for the entire area are available in the volume box.
You can change the reference terrain state in the reference box and the Cut/Fill map is automatically updated. Nevertheless, quantities values need to be recalculated using the recycle button in the volume box.
Cut/fill maps visualization settings
Now that the Cut/Fill map is available, let's make it better and easier to analyse. Select your Cut/Fill map within the viewport or through the project view to get access to SELECTION - TOOLS for Volume. First, set the Min. Cut/Fill value to highlight only significant earthwork areas. Using a 0.3ft (10cm) value typically clears noisy areas. Then, reduce the stretch value a little to enhance the color appearance.
Enable the Cut/Fill annotations to get a better understanding of the dirt movement. You can adjust color, size and spacing of the spotted height labels in the TOOLS ribbon.
Hint: Use the 2D view mode, your Cut/Fill map will look nicer.
Extract Cut/Fill areas
To go deeper in the earthwork analysis, break down the Cut/Fill map into smaller areas. Enable the Extract Cut/Fill Area tool and click on any cut or fill area. This area will be available as a separate volume item in the project view. By selecting it, you can view quantities related to that specific area in the volume box. Enable the Volume annotations to get a better understanding of the dirt movement. After breaking down all the relevant areas, you can export Cut/Fill values as a text file and create a more detailed report.
Cut/Fill analysis between terrain state and design
Now, we will compare a terrain state to the design to assess dirt that has to be moved to complete the project.
First, let's create a new terrain state for the design. Then we can import a DXF design file and convert the surface to a terrain. However, sometime design files come in 2D and don't contain any surface. In that case, import the 2D design file and edit contour lines and other elevation items to set Z values according to 2D plan annotations. When all geometries are available in 3D, triangulate to create a surface and convert it to a terrain.
Come back to your drone survey terrain state and use the construction site boundary to create a new Cut/Fill map. This time, use the design terrain state as reference.
Project monitoring over time
If you have multiple drone surveys, the Cut/Fill map can be pinned to be available on all the terrain states. In that way you can switch from a drone to another thanks to the terrain state tool and monitor the work progress through a nice time-lapse. To pin a Cut/Fill map, enable the pin icon related to that map within the project view.