discontinuity program which is able to calculate the seam stress and displacement in an underground mine. This program can also

Transcription

1 LAMODEL- This is a full-featured featured displacement- discontinuity program which is able to calculate the seam stress and displacement in an underground mine. This program can also reasonably calculate surface subsidence. Let s do a simple model using LAMODEL. In this tutorial, we will do a very basic model and make use of many of the automatic and default features of the program. The very first step is to define the problem we want to investigate.

2 Let s do a simple room-and-pillar production panel. First, we want to see the development loads, and then we want to look at the abutment stresses (i.e. stresses generated on the edges of gob) when the pillars are pulled. In this panel, we plan to have 7 entries each m 6 ft wide with 12 by 18 m pillars. The coal seam is 2 m thick and 200 m deep.

3 For this mining plan, a 3 m grid will work very well. This will enable us to use 2 elements across the entries and 4 by 6 elements for the pillars. Also, if we make the total grid dimensions 100 by 100 elements, or 300 by 300 m, we should be able to cover the area of interest and center it away from the grid boundary with room to spare.

4 To begin entering the parameters into the model, we need to start the preprocessor, LAMPRE. (If you have a PRE icon on your screen, you can double click on it, or you can use the start menu as shown below.) TO START: Click on: Start=>Programs=>WVU=>LaModel=>LamPre3.0.2 This will start LAMPRE, and the first thing that you may see is the Disclaimer. Click on: OK to accept the disclaimer i And the main LAMPRE window will appear.

5 To begin entering the parameters into the model, we need to start the preprocessor, LAMPRE. (If you have a PRE icon on your screen, you can double click on it, or you can use the start menu as shown below.) TO START: Click on: Start=>Programs=>WVU=>LAMPRE2 >WVU >LAMPRE2_1 This will start LAMPRE, and the first thing that you will see is the Disclaimer. Click on: OK to accept the disclaimer And the main LAMPRE window will appear.

6 In the main window, you see a menu bar and tool bar across the top of the window, and the LAMPRE 3.0 graphics in the middle. All of the parameter input is accomplished by primarily using the menu bar (or the tool bar) at the top of the window. Let s take a closer look at the menu bar

7 Click on: File on the menu bar A fairly standard Windows file menu appears. The user can: start a new file, open a LAMODEL input file, save, save as, close, exit, etc. The window also remembers the last few files that were previously opened at the bottom.

8 Click on: Edit_Data on the menu bar The commands for the primary data input submenus appear. These sub-menus are used to enter the numerical parameters into the input file for LAMODEL. We will look at these parameter input menus in much more detail in a few minutes. First, let s move over to the Edit-Grids Gid menu

9 Click on: Edit-Grids on the menu bar The sub-menus for editing the grids appear. These sub-menus are used to graphically enter the element grids for the input file to LAMODEL. We will look at this graphical input menus in much more detail in a few minutes. Before that, let s start with the parameter input forms.

10 Click on: Edit-Data on the menu bar Next Click on: Project Parameters to begin entering parameters for our model

11 In this form, we can enter a title, in this case Tutorial 1. Next we set: Number of Seams = 1 Number of In-Seam materials = 10 (we will see later that this will allow us to use a yield zone around the pillars) Number of Steps = 2 2 (The first step for development and the second step for retreat mining) Current Units = m, MPa (International units) When finished, Click on: the Next Form button

12 This opens the Seam Geometry and Boundary Conditions form. As discussed earlier, we will set: The Element Width to 3 m, the Number of Elements in X Axis to 100 and the Number of Elements in Y Axis to 100. We only have 1 seam, and we have no particular mine coordinates to use so we will leave: the X Coordinate of Grid Origin equal to 0 the X Coordinate of Grid Origin equal to 0, the Y Coordinate of Grid Origin equal to 0

13 Then, also as discussed earlier, we will set: the Overburden Depth to 200, and the Seam Thickness to 2 (see above)

14 There are 2 possible Seam Boundary Conditions that LaModel can use, Rigid or Symmetric and, of course, 4 sides to the model Without going into the details of the different boundary conditions, let s set the North and East boundary to Symmetric, and the South and West boundary to Rigid id in order to observe the difference it makes in the model results. When finished, Click on: the Next Form button

15 This opens the Overburden / Rock Mass Parameters form. If we had site-specific rock mass data, or some experience/engineering judgment, we might adjust these parameters to better fit our location. However, since we do not have any site-specific information, we can just use the default values and we will get reasonable overburden response. To continue, we click on: the Next Form, button

16 This opens the In-Seam Material Wizard form, on the Elastic-Plastic for COAL tab. This wizard helps the user automatically generate Mark-Bieniawski coal strength materials and is used in conjunction with the automatic yield zone generator in the grid editor to produce coal pillars that follow the Mark- Bieniawski i coal strength th formula. First, a little bit of background

17 The Bieniawski Formula for coal pillar strength is as shown: Where the strength of the pillar (S P ) is a function of the insitu coal strength (S i ) and the width (w) to height (h) ratio of the pillar.

18 The Bieniawski Formula implies a stress gradient within the pillar. This stress gradient can be calculated as shown: Wh th t ( ) t i t di t Where the stress (σ v ) at a point x distance inside the pillar is a function of the insitu coal strength (S i ) and the height (h) of the pillar.

19 Once the stress gradient is known, the strength of a rectangular pillar can be determine using the Mark-Bieniawski Formula as shown: Where the strength of a rectangular pillar (S P ) is a function of the insitu coal strength (S i ) and the width (w), height (h) and length (l) of the pillar. The coal wizard in LaModel will automatically implement pillars with a Mark-Bieniawski strength.

20 When the Bieniawski coal pillar strength formula is implemented in LaModel, the elements in a pillar increase in strength in proportion to the distance from the edge of the pillar. This strength increase is nominally due to the confinement provided by the surrounding coal. As in the figure above, we end up with concentric zones of material around the pillars (two materials per zone, an edge and a corner material). The coal wizard helps us automatically define the coal properties needed to fill these concentric zones.

21 When we talk about Yield Sets, we are referring to sets of coal properties for different seams and/or coal thicknesses. In our case, we only have one seam, so we only need 1 yield set. When we talk about Yield Zones, we are referring to the number of concentric rings of yielding material around a pillar that we want to use for the yield zone. We need to define a yield zone that will encompass the expected distance of yielding into the pillar. In our case, we will use a 4 element thickness (12 m). We should not have any yield deeper than this into the pillar.

22 So, in the Coal Wizard, we will enter: 1 for the Number of Sets to be Defined 4 for the Number of Yield Zones per Set We will use the default values for: Coal Modulus, Plastic Modulus and Coal Strength To actually define the material properties, we click the Define Set button

23 This opens a pop-up window that informs the user that M-B coal properties are going to be automatically generated, and ask if the use wants to continue So, in the first pop-up window, we click the Yes button to continue

24 Then another informational pop-up window opens that informs the user that no material models are presently defined, and 9 COAL materials, A-I will be created, So, in the second pop-up window, we click the Yes button to continue

25 Finally, a third informational pop-up window opens that informs the user that 9 Coal material models (A I) have been defined. So, in this third and final pop-up window, we click the OK button to continue. Back in the Elastic-Plastic for COAL Wizard, Back in the Elastic Plastic for COAL Wizard, we click on: the Strain-Hardening for Gob tab to continue

26 This opens the Strain-Hardening for GOB Wizard form. First, a little background

27 The gob wizard is intended to simplify the task of determining gob material properties and to allow the user to obtain fairly accurate gob properties in the initial model run. To accurately simulate the gob zone in LaModel, an exponential strain-hardening behavior is generally most appropriate and best matches that t observed in the laboratory; therefore, this Strain-Hardening is the material model used by the Gob Wizard.

28 The Wizard s technique for pre-calculating accurate gob properties consists of determining a target level for the gob stress (based on overburden and gob width), then using the model parameters to approximately calculate expected convergence, and finally backcalculating the gob properties that provide the desired gob stress and convergence using a simplified two dimensional calculation. The critical parameters that we need to enter are: The Width of Gob Area and the % Overburden Load on Gob

29 For our model, we will enter: 380 ft for the Width of Gob Area (rib-to-rib), and We will check the Use the Suggested Value Box to use the recommended 35% overburden load on the gob (based on a 21 degree abutment angle). We will use the given and/or default values for the: Seam Thickness, Overburden Depth, Coal Properties and Gob Default Parameters

30 (Note: on some computers, before running the Gob wizard, the input file needs to be saved.) So, to actually calculate the required gob properties, We Click the Calculate Button,

31 This opens a pop-up window that informs the user that the calculation will determine the Final Gob Modulus required to get the desire Gob Stress. So, in the first pop-up window, we click the Yes button to continue

32 and you will see the Final Modulus for the Gob set to an appropriate value To then save these properties to our material set, We click the Define Set Button

33 This opens a pop-up window that informs the user that the calculated Gob Material has been saved. To continue, we click the OK button to continue

34 At this point, let s take a look at the materials that we have defined. Click on the Material Summary button and a window appears showing us the present materials and their parameters. We see material A A is Linear Elastic with parameter #1 = 2068 (MPa, the Elastic Modulus) and parameter #2 = 0.33 (the Poisson s Ratio). This is the core material for our yielding coal properties. p We also see out Strain-Hardening Gob with parameter #2 = (MPa, the Final Modulus)

35 If we want to know more about the material models and the parameters that are necessary for defining the materials, this figure provides a quick reference. To get out of the Material Summary, we click the OK button and to continue entering parameters, we click on the Next Form Button in the Gob Wizard

36 This opens the Program Control Parameters form. This is the last form for entering parameters. The parameters in this form control the calculation of the stresses and displacements in the LaModel program. In general, the default values will work for the majority of models. We just want to Check the box for Calculate l Safety Factors and use the remaining defaults for our example. To finish entering parameters, we click the gp, Finish button

37 As an alternative technique for inputting material properties, let s take a look at the Material Editor window. To do this, we click on: Edit_Data->Material Models-> Edit In-Seam Materials Models from the menu bar, This opens the In-Seam Material Models form. This is the original form for entering material parameters and gives the user complete control over specifying various material types and parameters

38 In the In-Seam Material Models form, we can change the current material by typing a new number in the Current Material Number edit box or by using the slider. We can edit any of the Material Types by changing the In-Seam Material Type radio buttons. And then set the desired Material Constants t in the appropriate edit boxes.

39 To set the default gob properties, lets slide the Current Material Number slider to the far right, to Material Number, 10, and Material Code, J. Then, let s change the Final Modulus to 2069 MPa, A good default value. To finish entering parameters, we click the OK button.

40 At this point, lets save the file. Go to the File pull-down menu and Click on Save and save the file to your desired location. Enter OK to a number of pop-up notifications about no seam materials yet. That will be next.

41 This brings us back to the main LAMPRE window. Next we want to graphically enter the material codes for the seam grid. To do this, we click on: Edit_Grids->Edit_Grids from the menu bar, The opens the Grid Editor window

42 The Grid Editor essentially works like a spreadsheet. Material codes for individual cells may be set by clicking on a cell and then typing an appropriate letter from A to Z. Blocks of cells may be changed by clicking and dragging the mouse over a range, and then typing the material code. O ti / l b l t d d Or, entire rows/columns may be selected and changed using the row/column number.

43 Also, a block of cells may be copied and pasted (greatly simplifying the creation of numerous pillars). Finally, the grid editor allows for automatic yield zone generation based on materials that were automatically defined using the coal wizard We will use all of these techniques to define the materials codes for our room-and-pillar production panel. (Note: at this point, it is a good idea to set the Caps Lock on the keyboard, since we will only be working with capital letters in the grid editor)

44 First, Let s make the Grid Editor window full screen by clicking on the middle button in the upper right corner of the window. Then, let s zoom in or out a bit to get the, approximate view above, by clicking twice on the left arrow on the Zoom slider.

45 Now, Let s start defining the middle (or belt) entry of our panel by selecting the headings for columns 50 and 51. (This is in the exact center of the grid.) Now enter a 1 from the keyboard to fill these columns with the numeral 1 to represent an opening. Repeat this for columns 32-33, 38-39, 44-45, 56-57, 62-63, to define the 7 entries

46 Repeat adding 1 to the columns Repeat adding 1 to the columns 32 33, 38 39, 44-45, 56-57, 62-63, to define the 7 entries

47 When finished with the entries the grid should When finished with the entries, the grid should look something like this.

48 Next, Let s start defining a couple of crosscuts. To do this, click in cell (33, 100) and drag to cell (68, 100). Now enter a 1 from the keyboard. This creates half a crosscut at the top of the screen. Now, click in cell (33, 93) and drag to cell (68, 92). Enter a 1 from the keyboard. This creates a full crosscut with 40 by 60 ft pillars R t f 3 t t d fi th t 4 Repeat for 3 more crosscuts to define the top 4 rows of pillars.

49 When finished with the top 4 rows of pillars, the gird should look something like this. (Note: you may need to adjust the zoom appropriately)

50 Next, Let s copy these 4 rows of pillars the rest of the way down the grid To do this, click in cell (33, 100) and drag to cell (68, 69). Now go to the Edit menu and select Copy Range.

51 Then, click in cell (33, 68) and drag down and over to at least cell (68, 36). (You can cover more than the copy area and only the copied area will be inserted from the top left corner) Now click Edit=>Paste Range (Note: you can also use the classic Windows short-cut keys Ctrl-C to copy and Ctrl-V to paste)

52 Continue copying and pasting the pillars the rest of the way down the grid. You should end up with exactly half a pillar at the bottom of the grid.

53 Now would be a good time to save the grid. Go to the pull-down menu Grid->Save Grid

54 Next, scroll to the upper left corner of the grid, and let s apply the yield zones. Click on the Apply Yield Zone button A message appears describing the yield zone to be applied. Click the Yes button to continue.

55 The material properties around the coal edges The material properties around the coal edges are changed to reflect the yield zones defined previously in the Coal Wizard

56 Now, let s work on the second step. Click Grid->Save to save the grid for the first step. Slide the Current Step Number slider to 2 to bring up the default second step grid.

57 Click Grid->Load From to load the first step grid into the second step grid.

58 This opens a form for selecting the seam and step number for the grid to load Select: 1 for the Step Number, and 1 for the Seam Number Click OK to continue

59 This fills step 2 with the grid from step 1.

60 Step 2 is retreat mining. Here we will replace half of the pillars rows (six rows) with gob material. To do this click on grid cell (33, 100) and drag the mouse to cell (68, 53). We then type the letter J. This will change all the selected cells to J the GOB material.

61 Save this grid. Click Grid->Save Grid to save the grid for the second step. Click Grid->Exit to exit the grid editor

62 In the LAMPRE window, let s save this input file as Tutorial 1.inp Click File=>Save As, In the Save LAMODEL form, change to the desired directory and enter Tutorial 1 for the Filename

63 Now, we want to submit the input file to the LaModel solution module and calculate the seam displacements and stresses. If you have a LAM icon on your screen, you can double click on it, or you can use the start menu by Clicking on: Start=>Programs=>WVU=>LaModel3.0=>LaMo del3_0_4.exe Either of these actions will start LaModel, and the first thing that you will see is the main LaModel window.

64 In this main window, there is a very simple main menu bar with only a File menu. Also, there are a number of informational text boxes which help track the progress of the program. (At this point, we are not going to go into details about any of these informational boxes.) And there is a Run and Exit button.

65 We can see that the Calculation Phase information box is stating: Waiting for File-> Open And really, the two main functions of the LaModel program are to open files and then to solve for the displacements and stresses. So, to open the previously created input file, we click on: File->Open, and locate and select your input file, Tutorial 1.inp.

66 Hopefully, you will get a poop;-up window that says your Input Files was Successfully Read. Otherwise, you will need to go back and check/fix your input file. To dismiss the pop-up window, click the OK To dismiss the pop up window, click the OK button

67 Now, we can see that the Calculation Phase information box is stating: Waiting for Run At this point, Click the Run Button to run LaModel

68 When it is done running, we can see that the Calculation Phase information box is stating: Finished At this point, Click the Exit button to exit the LaModel program.

69 Now, we want to look at the output from LaModel in the post-processor, LamPlt If you have a PLT icon on your screen, you can double click on it, or you can use the start menu by Clicking on: Start=>Programs=>NIOSH=>LaModel3.0=>La mplt3_0 Either of these actions will start LamPlt, and the first thing that you will see is the main LamPlt window.

70 The main LamPlt window will appear.

71 We now need to open the output file from LaModel In the LamPlt window, Click on: File->Open

72 In the Open form: change to the necessary directory, select the Tutorial 1.f1 file, Click Open This will open the Tutorial output file and bring up a 3D colored-square plot of the convergence.

73 This is a typical LamPlt colored square, or pseudo 3D, plot. For this plot, the desired value for each element in the grid is plotted as the appropriate scaled color. The majority of the analysis in LamPlt is accomplished through the Plot Options form To get to this form, click: Edit=>Colored Square Plot (or use the red icon button)

74 Using this form, we can: Examine various Stress Items, Adjust the Color Palette,, or Adjust the Scale.

75 For Example, Lets look at the 3D plot of the stress distribution for Step 2 Set the Stress Item Radio Buttons to Total Vertical Stress, by Clicking the appropriate Radio Button Set the Step Number to 2, by entering a 2 in the box or using the slider Click OK

76 This brings up the colored square plot of the vertical stress for the second step. Next, let s look at a cross section of the stress in the fourth column of pillars. To get to the cross-section form, click: Edit=>Cross-Section Plot

77 In the Cross Section Options Form, we need to click on: Total Vertical Stress 2 for the Step Number Parallel to Y for the Cross Section Direction, and 53 for the Cross-Section Location (a line up the middle of the fourth pillar row) Then click the OK button to continue and make the new plot

78 In the main LAMPLT window, we now have a 2- D plot of the vertical stress at column 53. (To edit these 2-D plots, you can right click in the window to bring up an extensive dialog box of editable properties.) (Also, you can copy the graphics to the windows clipboard using Edit=>Copy, and then paste the graphics into most windows programs.) Thi l d th ffi i l t t i l l t This concludes the official tutorial, please try a number of other plot options to examine the second step, at your leisure.