Tutorial #2 highlights examples of how Carlson handles outcrop and subcrop conditions on several examples involving ridge top mines as well as sub-cropping reserves. Accurately locating the crop is one of the first things the engineer needs for laying out a surface mine. Carlson automatically detects the location of the crop within the Surface Mine Reserves command. Volumes will never be calculated from above the ground surface. The advantage of the Draw Outcrop routine is that it allows the user to witness where the program is interpreting outcrops and subcrops. It is also useful in establishing a starting perimeter for pit layout. Outcrops are automatically calculated and drawn using Draw Outcrop command under StrataCalc on the fly directly from the drillhole data, or from pre-calculated grids.
For Generating Outcrops Directly from Drillholes ("On the Fly")
For Generating Subcrops
Outcrop Procedure
Select Draw Outcrop in the StrataCalc menu. Fill in the Outcrop
Settings
dialog box. The user can specify the source for surface topography
(grid file or
screen selection) and what layer to store the outcrop in when it is
drawn. The
user normally will use the settings as shown in the dialog box below
with one
exception. The offset distance could be set to 0.1 to 1.0 ft
to reduce the vertices in the outcrop when drawn. Otherwise, the
polyline for the outcrop will
contain an unnecessarily large number of points.
Command: outcrop
Select surface entities & at least 3 drillholes
Select objects: Specify opposite corner: 111 found
Use drillhole surface elevations in surface model [Yes/<No>]? Y
if they match the contours, otherwise N
Reading points ... 79695
Ignored 562 points with zero elevation.
Ignored 36 duplicate points.
Intersections found 80377
Pass> 10 Null Z values left> 0
Finding splits ...
Finding pinch out ...
Calculating seam stacking ...
Output grids for strata and surface [Yes/<No>]? N The
files may be saved out for other uses.
No is the typical response.
Choose modeling method
[<Triangulation>/Inverse dist/Kriging/Polynomial/LeastSq]?
Apply global trend to strata extrapolation [Yes/<No>]? Y
Use Triangulation Subdivision [Yes/<No>]? N
Triangulating points ... 5
Assigning grid values> 98400
Pass> 282 Null Z values left> 0
Contouring elevation 0.0
Inserted 348 contour vertices. Complete the Make Grid File dialog box. The user may select the total number of rows and columns or the grid spacing pattern option. The program creates the grids "on the fly" from the drillhole data.
Select the preferred method. Once the gridding method is selected the Choose Strata dialog box appears. Choose the strata to process. Each strata can be gridded using independent gridding algorithms. If Inverse Distance or Least Squares was selected as the gridding method, when the strata is selected, the user is prompted for the power to be used in the algorithm. Once the power is entered, assuming Inverse Distance or Least Squares is the selected method, the user is prompted for other strata to be processed. The user can select any number of strata to be processed by holding down the CTRL or SHIFT buttons.
Outcrop lines are produced on elevation zero. To raise the outcrop to the surface, use the command 2D to 3D Polyline by Surface Model command in the DTM Module. This uses the surface model as the basis for assigning elevation to the outcrop polyline.
Making Fence Diagrams
As a way to verify the location of the outcrop or make a graphic
presentation, a fence diagram can be created using the
Fence Diagram command under
Stratacalc. Fence diagrams are useful for presenting geologic
data
as well as verifying the proper location of seams and their burden.
Shown below is a fence diagram taken from the line drawn from west to
east through the outcrops on the hill.
Fence Diagram Procedure and Prompting:
Command: fence
Select polyline to pull fence diagram
from: Pick the polyline to get the fence from
Use drillhole surface elevations in
surface model [Yes/<No>]? N
Select surface entities and at least 3
drillholes. Select the drillholes and surface contours
Select objects: Specify opposite
corner: 112 found
Reading drillhole 5
Finding splits ...
Finding pinch out ...
Calculating seam stacking ...
Ignore zero elevations
[<Yes>/No]? Y
Reading points ... 79695
Choose modeling method
[<Triangulation>/Inverse dist/Kriging/Polynomial/LeastSq]? I Choose
a modeling method you prefer.
Use inverse distance to which power
[First/<Second>/Third/Other]? S
Use elliptical inverse distance
[Yes/<No>]?
Calculating grid by inverse distances
98456...
Bottom elevation of grid
<1650.00>: 1400
Pick the lower left corner for the
diagram: Pick an open area in the drawing for the lower left
corner of the diagram.
Using Surface Reserves to Check the Outcrop Volumes
To prove that Carlson honors the outcrop in its
calculations, layout a rectangular polygon that overlaps the
outcrop area. If Surface Mine Reserves recognizes the seam crop, then
the area
of the seam will be less than the area of the perimeter, and
the upper seam crop area will be less than the lower seam area. It
calculates reserve areas and handles outcrops automatically. Higher
surfaces (the topography in this case) are the limiting factors.
Volumes will never be calculated above the next surface up.
The area of the perimeter is shown as 3.371 Acres, some of it within the area of coal, and some outside. Run the Surface Mine Reserves command using the perimeter to get the tons and acres of coal. A typical report from the Surface Mine Reserves command under StrataCalc is shown below. Reports are user-defined in the Report Formatting dialog box.
As the report indicates, Carlson recognizes the limits
imposed at the outcrop. It successfully truncates the seam at the
outcrop and reports
the included area between the crop and rectangle. Notice the C1 has
less acres than the C2 because it crops out higher on the slope. the C2
shows 2.192 Acres compared to the full 3.371 Acres of the polygon. The
Pit Acres are reported as an available option in the Formatter.
In topographic situations similar to the one shown in this example, for coal, the user will have to deduct from the mineable reserves for crop loss. Crop loss sometimes runs 10' to 15' vertically. The coal in this zone is usually oxidized to such an extent that the BTU is so low and the ash is so high, the coal cannot be sold for steam product, and chemistry is so poor that it cannot go for metallurgical product either. Oxidized coal is treated as overburden.
Using Outcrops for Laying Out Pits
In the example below, the outcrop was used to define the limits of
the surface mining pits.
The outcrop defined the limits of mining on each side of the pit. The
direction of mining was input
as part of the pit layout routine. The
example below shows the Pit Layout By Advance command executed on
the closed polylines.First, create a close polyline of the
outcrop/mine boundary. Use the command Draw-Boundary
Polyline and pick inside the ridge/outcrop lines to get a
new interior polyline. You can also use AutoCAD's
BPOLY command. Then, draw a direction line down the ridge to assign
direction. Pits will be cut perpendicular to this line.
Pit Names, Labels, and Identify Pit Names
Since the process of laying out pits using the Pit Layout By Advance
option gives the pits a name, a discussion of naming and labeling
procedure is helpful at this
point. After the pits are drawn, there are two methods to draw the pit
name labels. Go to Label Pit Polyines or Pit Label Formatter. Identify Pit Polylines allows the user to see
the Pit Names when the labeling
option was not selected.
Subcrop Procedures
Subcrops occur where the
unconsolidated material (could be glacial
till or a channel deposit) has eroded out the key
seam below the surface. Subcrops differ from pinchouts, in that unlike
pinchouts, which can
occur anywhere below the surface, lower strata being eroded by the
unconsolidated material cause subcrops. Unlike outcrops which can be
created "on the fly" from
drillhole data, subcrops are calculated from grids. To calculate
subcrops, the user must have the
surface grid, thickness grid of the unconsolidated material, and bottom
elevations of the strata to test
for subcropping. In addition
to the gridding algorithms, the user can specify strata limit polylines
to override the
natural mathematical interpretation of the data.
When Carlson calculates the subcrop it starts from the surface and
works down through
the grids. If an upper grid has a lower elevation lower than that of a
lower grid, the elevation of the
upper grid is set to the elevation of the lower grid. This leads to a
zero thickness in the lower grid, or
a subcrop. Select the File option to begin calculating the subcrop.
Carlson
allows the user to calculate
the subcrop from a pre-calculated grid or directly from
the drillhole data.
This example was created by making strata grids from the drillholes. Put them in the PreCalc grids file and then generate a Fence Diagram. The outcrop coincides with the outcrop lines in plan view on the hill side. Notice how the glacial till is subcropping the upper coal seam and the parting.
Strata Limit Polylines
Using the same example for the Subcrops above, we will now
create Strata Limit Polylines for both the coal seams and the parting.
They must be drawn in plan view, then named with Name Strata Limit
Polylines. Strata Limit Polylines must be turned on under
Configure , Mining Modules. There are options to use them, and
to automatically select them. The orange lines are limit lines. The
interior line is an Exclusion for the upper coal seam. The outer line
is an Inclusion for the lower coal seam. Volumes will be calculated
accordingly with Surface Mine Reserves.