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4 - Support

This tutorial demonstrates the various ways of modeling support to increase the wedge Factor of Safety. All of the methods of modeling support in SWedge simply represent different ways of applying a force to a wedge. These methods include:

  • Bolts can be added with the Add Bolt option.
  • Shotcrete can be applied with the Shotcrete option.
  • An average support or loading pressure can be applied with the Pressure option.
  • Forces can be applied with the External Force option.

Topics Covered in this Tutorial

  • Bolts
  • Shotcrete
  • Pressure
  • External Force
  • Sensitivity Analysis

Finished Product:

The finished product of this tutorial can be found in the Tutorial 04 Support.swd7 file, located in the Examples > Tutorials folder in your SWedge installation folder.

1.0 Creating a New File

If you have not already done so, run the SWedge program by double-clicking the SWedge icon in your installation folder or by selecting Programs > Rocscience > SWedge > SWedge in the Windows Start menu.

When the program starts, a default model is automatically created. If you do NOT see a model on your screen:

Select: File > New

Whenever a new file is created, the default input data forms valid slope geometry, as shown in the image below.

Default SWedge model forming valid slope geometry

If the SWedge application window is not already maximized, maximize it now so that the full screen is available for viewing the model.

Notice the four-pane, split screen format of the display, which shows Top, Front, Side and Perspective views of the model. This view is referred to as the Wedge View. The Top, Front and Side views are orthogonal with respect to each other (i.e., viewing angles differ by 90 degrees.)

2.0 Model

2.1 PROJECT SETTINGS

Let's start by setting up the project in the Project Settings dialog. Select Project Settings on the toolbar or on the Analysis menu.

Select: Analysis > Project Settings

  1. Select the General tab.
  2. Make sure the Analysis Type is Deterministic.
  3. Make sure Units is set to Metric, stress as MPa.
  4. Click OK..

2.2 INPUT DATA

Now let’s define the slope and joint properties in the Input Data dialog. To open the dialog, select Input Data on the toolbar or on the Analysis menu.

Select: Analysis > Input Data

  1. Select the Slope tab.
  2. Set Slope Height (m) = 20.
  3. Keep all other parameters as is.
  4. Click OK.

Combinations Input Data

3.0 Adding Bolts

We'll start by adding a bolt to the wedge using the Add Bolt option.

3.1 BOLT PROPERTIES

We first need to set up bolt properties using the Bolt Properties dialog. Select Bolt Properties on the toolbar or on the Support menu.

Select: Support > Bolt Properties

  1. Select Bolt Property 1.
  2. Set Type = Simple Bolt Force.
  3. Set Bolt Model = Active.
  4. Set Force = 0.2.
  5. Click OK.

Bolt Properties dialog

3.2 ADDING A BOLT

Next we'll add the bolt to the wedge using the Add Spot Bolt dialog. Select Add Spot Bolt on the toolbar or on the Support menu.

Select: Support > Add Spot Bolt

  1. Mouse over the Wedge View so the cursor is over wedge on the slope face.
  2. When the cursor changes from to , click the left mouse button at a point on the wedge where you want the bolt installed (e.g., on the slope face).
    The Add Spot Bolt dialog opens, allowing you to modify the geometry and set up properties for the bolt.
  3. Keep Orientation = Trend / Plunge.
  4. Set Trend = 5.
  5. Set Plunge = 25.
  6. Click OK.

Add Spot Bolt dialog

A computation of all the wedge combinations occur. Each wedge includes a bolt of Bolt Property 1 with a Trend / Plunge of 5/25. After computation, notice that the minimum Factor of Safety wedge has changed from 0.9886 to 1.0087.

Repeat the above steps to add a few more bolts to the wedge with larger bolt capacities and note to the effect on the Factor of Safety.

TIP: Note that the colour of the bolt on the model matches the colour of its Bolt Property in the Bolt Properties dialog.

NOTE: For detailed help on how bolts are implemented, see Overview of Support in SWedge and the other topics in the Support section of Help.

3.3 DELETING BOLTS

You can delete bolts from a wedge using the Delete Bolt option.

To delete one or more bolts from a wedge:

Select: Support > Delete Bolt

  1. Mouse over the wedge on the Top, Front, Side, or Perspective pane.
    Note that the cursor changes to a box.
  2. Place the cursor over the bolt that you want to delete.
    The bolt changes colour to indicate it's selected.
  3. To delete the selected bolt, click the left mouse button.
    Note that a new Factor of Safety is immediately calculated.
  4. Repeat the steps above to continue deleting bolts.
  5. To exit the Delete Bolt option, press the ESC key.

To delete ALL bolts at once:

Select: Support > Delete Bolt

  • Enter the asterisk ( * ) character on the keyboard.

3.4 EDITING BOLTS

You can edit the properties of a bolt using the Edit Bolt option.

Select: Support > Edit Bolt

  1. Mouse over the wedge on the Top, Front, Side, or Perspective pane.
    Note that the cursor changes to a box.
  2. Place the cursor over the bolt that you want to edit.
    The bolt changes colour to indicate it's selected.
  3. Click the left mouse button to open the Edit Spot Bolt dialog.
  4. Edit properties of the bolt the same way you did when adding the bolt above.
  5. Click OK.

NOTE: Bolt properties must be edited one at a time. It's not possible edit the properties of multiple bolts simultaneously.

Edit Spot Bolt dialog

3.5 VIEWING BOLT PROPERTIES IN THE INFO VIEWER

You can view a list of all the bolts in a model and their properties in the Info Viewer. To open the Info Viewer, select Info Viewer on the toolbar or on the Analysis menu.

Select Analysis > Info Viewer

Info Viewer

3.6 VIEWING BOLTS

It is useful to note that, if you move the wedge out of the slope after adding bolts, the bolts stay “in” the slope and are completely visible. This allows you to examine the bolt installation in more detail.

To move the wedge out of the slope:

  • Click and drag the wedge with the left mouse button.

4.0 Adding Shotcrete

You can add shotcrete support to a wedge model using the Shotcrete option. To open the Shotcrete dialog, select Shotcrete on the toolbar or on the Support menu.

Select: Support > Shotcrete

  1. Select the Shotcrete (Slope Face Only) check box.
  2. Set Thickness (m) = 0.1.
  3. Set Shear Strength (MPa) = 1.
  4. Click OK to re-compute the analysis.

add shotcrete support

Notice that the addition of the shotcrete layer has increased the Factor of Safety from 1.0808 to 1.5983.

TIP: To perform a parametric analysis and view the effect of different Thickness and Shear Strength parameter values, you can click the Apply button to re-compute the analysis without closing the dialog.

NOTE: Note that shotcrete is applied only to the slope face of the model. When you click OK or Apply in the dialog, notice that the slope face is shaded in gray to indicate the presence of shotcrete. Also note that shotcrete is NOT applied to the upper slope of the model.

NOTE: For detailed help, see Applying Shotcrete in SWedge

5.0 Pressure Support

Next we'll look at adding support to a wedge using the Pressure option. Before continuing, delete bolts and shotcrete from the model following instructions in the sections above.

  1. To open the Pressure dialog, select Pressure on the Support menu.
  2. Select the Slope Face check box to apply pressure to the slope face only.
    By default, the direction of the applied pressure is normal to the slope face.
  3. We want to apply normal pressure, so keep Trend = 5 and Plunge = 25.
  4. Set Pressure (MPa) = 0.01.
  5. Keep Model = Active.
  6. Click OK.

 Pressure dialog

Note that the Factor of Safety is increased to 1.197.

6.0 Sensitivity Analysis

A Sensitivity analysis in SWedge allows you to quickly determine the effect of any input variable on the Factor of Safety. The feature is especially useful for determining support requirements. In this tutorial, we'll demonstrate this by using a Sensitivity analysis to determine the support Pressure required to achieve a Factor of Safety of 1.5.

To conduct a Sensitivity analysis, select Sensitivity on the toolbar or on the Analysis menu to open the Sensitivity Input dialog.

Select: Analysis > Sensitivity

  1. Select the first check box in the dialog and select Slope Pressure from the drop-down.
  2. Set From = 0 and To = 0.05.
  3. Click OK.

Sensitivity Input dialog

A Sensitivity chart is displayed, plotting the Factor of Safety vs. Slope Pressure.

  • Right-click in the chart and select Sampler > Show Sampler from the popup menu.

Show Sampler

The Sampler appears as a horizontal line on the plot.

  • Click and drag the Sampler until you obtain a Factor of Safety of approximately 1.5.
    The corresponding Slope Pressure of 0.023 MPa is also displayed on the plot.

Factor of Safety vs. Slope Pressure

  1. Close the Sensitivity plot.
  2. Select Pressure on the Support menu to re-open the Pressure dialog.
  3. Set Pressure (MPa) = 0.023.
    You should obtain a Factor of Safety of approximately 1.5.

7.0 Equivalence of Support Methods in SWedge

We will now demonstrate the equivalence of the various support methods in SWedge.

In the Wedge Information Panel in the Sidebar, note that Area (slope) = 198 m2. This is the area of the wedge face on the slope. If we multiply this area by Pressure (MPa) = 0.023, we obtain a force of about 4.55 MN. Therefore, if we add a single, simple force bolt with Force (MN) =4.55, we will get a Factor of Safety of 1.5.

The slight different in values is due to the fact that we did not obtain a very precise value of Pressure from the Sample option on the Sensitivity plot. Also note that, in both cases. support Model was set to Active.

8.0 External Force

Finally, we'll demonstrate that an External Force of 4.55 MN, applied normal to the slope (Trend/Plunge = 5/25), will also give us a Factor of Safety of 1.5.

  1. Select Pressure on the Support menu.
  2. In the Pressure dialog, deselect the Slope Face check box.
  3. Open the Input Data dialog.
  4. Select: Analysis > Input Data

  5. Select the Forces tab.
  6. Add an External Force as shown in the figure below.
    Deterministic Input Data
  7. Click OK.

The Factor of Safety is confirmed as 1.50.

NOTE: An External Force is always applied as an Active force and is equivalent to a bolt force with the same capacity and direction, if the bolt force is Active. Bolts and External Forces are NOT equivalent, if the bolt model is Passive.

This concludes the tutorial.

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