Introduction to LaModel: Understanding Element Types, Grid Creation, and Topography Files
In this article, I tried to explain element and cell types briefly, how to create grid files, (1) using LaModel New Grid Editor for simple layouts, (2) using AutoCAD Stability Mapping add-in for complex layouts, and how to generate topo file. Also, I pointed out a few important points.
Element types
1 -?Linear Elastic: A material that deforms proportionally to the applied load and returns to its original shape when the load is removed.
2 -?Strain-Softening: A material that initially deforms elastically, but as strain increases, it gradually loses strength, leading to softening behavior.
3 - Elastic-Plastic: A material that deforms elastically up to a certain yield point, after which it deforms plastically, meaning it permanently deforms without additional load increase.
4 -?Bi-linear Hardening: A material that exhibits two stages of hardening after yielding: an initial elastic response followed by two distinct plastic hardening behaviors with different stiffness.
5 - Strain Hardening: A material that becomes stronger and more resistant to deformation as it undergoes plastic deformation, requiring more stress to continue deforming.
6 - Linear Elastic Gob: A specialized element representing gob material (collapsed waste rock) that behaves elastically, with a linear stress-strain relationship, but typically with lower stiffness than intact rock.
Choosing the correct element type is crucial for accurate modeling, as different materials exhibit unique deformation behaviors under stress. For each element type, there are different material properties. The picture below shows the material properties of each element.
To better comprehend the background processing of LaModel’s material wizard, it's important to understand the concept of a concentric ring. The concentric ring structure plays a key role in how the material wizard calculates pillar strength in LaModel. Below is an excerpt from my thesis* that explains this briefly, you can check the references to dig more into this:
“Heasley* (2010) used concentric rings of different materials and separates the pillar into different types of cell elements to model the strength of materials in LaModel software. Two pillar cell equations are identified: (i) rib cell and (ii) corner cell. Because of their additional confinement, the defined core cells are stronger than the rib cells, which are stronger than the corner cells. “
Important Note: When using the ‘Linear Elastic’ element in your pillars, the stability factor will not be shown, as the model assumes that the pillar will not fail under any conditions. The same thing happens when you use ‘Gob’ element because the model assumes it will fail in any conditions. Therefore, if you can not see the safety factor of your pillar, check the element types in the pillar. Even if one ‘Linear Elastic’ or ‘Gob’ element is touching your pillar, the safety factor does not show up. Here is an example:
A is a linear elastic element where all the other elements are strain softening.
Create Grid file
There are two different methods you can use depending on how complex your layout is.
1-????? LaModel New Grid Editor (for simple layouts)
Click ‘Edit-Grid’.
‘1’ represents entries. You can create your mine layout by manually entering the entries.
Then click “Apply Yield Zone’ and ‘Yes’. Then LaModel will assign the materials accordingly.?
This method is easy to apply and does not include different steps. However, it is not convenient for complex layouts.
2-????? AutoCad - Stability Mapping (for complex layouts)
·?Open an AutoCAD file with the mine layout. ???????????
· Type “ARX†and click “Load†or type “Lâ€.
· Select ‘StabilityMapping.arx’ file.
· Create new layers for pillars and gob. Then move your pillar and gob polylines to related layers.
· Define element size and identify grid coordinates.
·? Type “SMAP_SEAMGRIDâ€.
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o?? Enter grid dimension inputs into related places (1)
o?? Select the layers for pillar and gob (2)
o?? Be sure the element code for gob is the same as the LamPre .inp file (!)
o?? Click “Build Grid†and “Save Gridâ€.
In the figure, green represents entries, red shows pillars, and yellow indicates gob. Then you should open the grid text file, copy the lines (except the first one), and paste in the .inp file that you created before. Open the .inp file with LamPre and click “Apply Yiend Zone’ and ‘Yes’. LaModel will assign the materials accordingly.?
Important notes:
· Be sure your StabilityMapping and AutoCAD versions are the same.
o?You can find StabilityMapping2023 at the link above, which means you'll need AutoCAD 2023. If I access a more up-to-date version of StabilityMapping, I’ll update the same link in the future.
· Be sure pillar and gob polylines are closed and in the right layers.
· Be sure the numbers of elements in the X and Y axes are the same in the grid file and .inp file. (red in the text figure)
Create Topo file
To generate .top file, we will use StabilityMapping again.
·?Type “SMAP_SEAMGRID†to generate a grid layout for the topography file.
o?? Enter grid dimension inputs into related places (1)
o?? Define contour layer, contour type, and units (2)
o?? Click “Build Gridâ€
o?? Name and place the .top file the same as your .inp file and “Save Gridâ€.
Important Note: An error will occur if the .top file is not named the same as the .inp file or if they are not placed in the same folder.
You are now ready to run the model in LaModel. Select the .inp file and click ‘Run’. The LaModel results will be saved in a .f1 file.
In the next article, we’ll dive into LamPlt, exploring how to display the results and save them using a basic Python script.
*References:
Ates, Mustafa Baris, "Integrated Large Discontinuity Factor, Lamodel and Stability Mapping Approach for Stone Mine Pillar Stability" (2022).?Graduate Theses, Dissertations, and Problem Reports. 11397. https://researchrepository.wvu.edu/etd/11397
Heasley, Keith & Sears, Morgan & Tulu, Ihsan & Calderon-Arteaga, C. & Jimison, L.. (2009). Calibrating the LaModel program for deep cover pillar retreat coal mining. 47-57.
Johnson, J. C., Whyatt, J. K., & Loken, M. C. (2014). A generalized method for calculating pillar cell capacities for boundary element modeling of coal mines. 2014 SME Annual Meeting and Exhibit, SME 2014: Leadership in Uncertain Times, 735–749