This command designs a pit into the existing ground surface using a set of dragline and bench slopes. The dragline slopes are for the portion of the pit excavated by the dragline and the bench slopes represent the truck-shovel excavation. The pit is drawn with 3D polylines and the pit volumes for the dragline and truck-shovel are calculated.
Before running this command, the base of the pit should be drawn as a closed 3D polyline. This pit polyline should also be assigned the elevations for the bottom of the pit. One way to set the elevation is to create a grid file for the bottom of the pit. For example, use Make Strata Grid Files to make a grid of the top of coal elevation. Then use the command 2D to 3D Polyline by Surface Model to convert the pit polyline into a 3D pit polyline with the grid elevations. This 2D to 3D command usually creates more vertices then necessary for Design Dragline Pit. So it is good to run Reduce Polyline Vertices.
Design Dragline Pit starts with the dialog shown below. All slopes are entered as percent. There is an option for two dragline slopes to allow for different slopes in different material, though it will be reported as one volume. The break point between these slopes can be set as either depth or at a grid surface. The grid surface could be a grid file for the transition strata. Next there is a dragline bench width and slope followed by cut and bench slopes. The cut-bench slopes repeat until intersecting the surface. The resulting modified surface can be saved as a grid file (.grd) with the Write Output Grid File option.
The program works by starting from the base pit polyline and applying the slopes until the surface is reached. The surface is modeled either by a grid file or from the entities on the screen. With the screen option, all 3D entities in the pit area are used to model the existing surface.
If a pit already exists to one side of the current pit, then this existing pit should be part of the surface model. Then the program will intersect the surface right away on this side without creating all the dragline and bench slopes. The Write Output Grid File allows you to save a grid file at the end of the command that represents the surface updated with the new pit. Then you can run Design Dragline Pit for the next pit and use the grid file output from the previous time as the new surface model.
The volume report shows the dragline cut and the truck-shovel cut. The dragline cut includes the volume from the pit base up to the top of Dragline Slope 2. The truck-shovel cut is the remaining volume up to the surface.
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| Plan view of dragline pit polylines |
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| Profile view of dragline pit slopes |
Pulldown Menu Location: Surface
Keyboard Command: minepit