This command creates a pit where the sides are a series of slopes with benches. The side slopes start from a pit closed polyline. This pit polyline can be either the bottom of the pit and the slopes run up and out to intersect the ground surface, or the pit polyline can represent the top of the pit and the slopes run down and in, to intersect the pit bottom grid. Different slopes can be used for different sides of the pit. The pit is drawn as 3D polylines and the pit volumes are reported.
Before starting this command, the pit perimeter should be drawn as a closed polyline, 2D at zero elevation. You also need grid files for the existing ground surface and the bottom of pit surface. Design Bench Pit starts with the dialog shown below where you specify these grid file names. 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 Bench Pit for the next pit and use the grid file output from the previous time as the new Ground Surface. The Round Exterior Corners option holds the slopes around the corners which makes the benches curve around the corners. Otherwise the side benches stay straight until they meet benches coming from other sides at the corners.
The Write Surface History File option will store a grid file for each pit bench and create a grid sequence file (.gsq) that can be used in two other commands. The View 3D Surface History command displays the grids in a 3D viewer. The Surface Mine Reserves command can use the grid sequence file to calculate and report the strata quantities for each pit bench. Also this command can prepare these quantities for use in Surface Equipment Timing.
The Process Multiple Polyline by Pit Names option allows you to process multiple pit perimeter polylines. The pit polylines must have pit/site names assigned and the program will process them in the order of their pit names. As each pit polyline is processed, the ground surface is updated with the pit volume removed. Then the next pit will use this updated ground surface. The Use Elevations From Pit 3D Polylines will start the pits at the elevations the polylines are drawn at instead of starting at the Pit Bottom Grid for going up, or the topography when going down.
The next dialog defines the cut and bench slopes. There are two dialogs with 7 slopes each for defining up to 14 cut and bench slopes. Pick the More Cuts button to switch between the two slope dialogs, 1-7 and 8-14. Cut slopes are entered as ratios. The cut depth can be either a fixed depth number or to a grid file. For a grid file, the program will find the intersection of the cut slope with the grid surface and will end the cut slope at this intersection. For example, you could make a grid file for a second coal seam and have the bench occur at this coal seam. After the cut slope, the bench slope and width are used. The cut and bench slopes are applied in order until there is an intersection with the surface. Once you have all the cut slopes defined, you can use the Save button to save these slope settings to a .PIT file. Then these settings can be recalled later with the Load button.
Besides the 14 cut and bench slopes, a different set of slopes can be defined for up to four different slope schemes. To define the another slope scheme, click the Next button. The set of slopes that you are currently editing is indicated by the Side number in the lower left. If you define different sets of slopes, then the program will prompt you to pick which sides to apply each set of slopes to. All sides are assumed to be slope type one. So you only have to identify types two, three and/or four. If only one slope group is defined, then you will not be prompted to select any additional sides.
If a pit already exists to one side of the current pit, then this existing pit should be part of the Ground Surface grid file. Then the program will intersect the surface right away on this side without creating all the bench-cut slopes.
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| 3D polylines created by Design Bench Pit showing three benches and a fourth bench in some places. Different cut slopes were used. On the North and South sides, the cut slope is 1:1. On the East and West sides, the cut slope is 3:1. |
Pick the pit polyline: pick the closed polyline
Pick pit polyline segment for side 2 slopes (Enter to continue):
pick the segment near midway
Pick pit polyline segment for side 2 slopes (Enter to continue):
pick the segment near midway
Pick pit polyline segment for side 2 slopes (Enter to continue): press Enter to continue
Pulldown Menu Location: Surface in Advance Mining
Keyboard Command: minepit2
File Names: \lsp\pond.arx, \lsp\minepit2.lsp,
\lsp\makegrid.dcl