Unwedge v Tutorial 3 Perimeter Support. Topics Covered:

Transcription

1 Unwedge v. 4.0 Tutorial 3 Perimeter Support Topics Covered: Perimeter support design view Wedge apex height Adding a bolt pattern Bolt properties Editing a bolt pattern Bolt data tips Bolt support force diagram Adding shotcrete Editing shotcrete Shotcrete properties

2 Introduction This tutorial will demonstrate how to add support to perimeter wedges using pattern bolts and shotcrete, in order to increase the safety factor of wedges which require support. The finished product of this tutorial can be found in the Tutorial 03 Perimeter Support.weg file. We will start with the same model used for Tutorial 1 (Quick Start tutorial), which represents an underground powerhouse cavern for a hydroelectric power generation project. Select: File > Recent Folders > Tutorials Folder, or use the drop-down arrow on the Open toolbar button to choose the tutorials folder. Select the Tutorial 01 Quick Start.weg file. Perimeter Support: Bolt Pattern To add support to perimeter wedges, you must be viewing the Perimeter Support Designer view. To switch to this view, select the Perimeter Support Designer option from the dropdown menu on the toolbar or the Select View sub-menu of the View menu. You should see the following view. Figure 1 Perimeter support designer view. The Perimeter Support Designer view is a 2-dimensional view which allows you to add or edit support (bolts, shotcrete or pressure) on the perimeter of the excavation. The view displays: The Opening Section boundary The perimeter wedges, in two dimensions, around the perimeter of the excavation The perimeter support which has been applied (bolts, shotcrete, pressure) The two-dimensional display of the perimeter wedges allows you to easily determine the extent of pattern bolting, shotcrete, or pressure which must be applied, in order to support the perimeter wedges. 3-2

3 Wedge Apex Height Before we add a bolt pattern, let s display the wedge apex height, so that we have an idea of the bolt length that will be required. The apex height is the shortest distance from the apex of a wedge to the excavation boundary, measured in the 2-dimensional plane of the Opening Section. 1. Select the Filter List button in the Sidebar. 2. In the Wedge Information Filter dialog, select the Defaults button to set the default checkbox selections (wedge name, safety factor, wedge weight). 3. Select the Apex Height checkbox. Select OK. 4. The Wedge Info panel in the Sidebar should now include Apex Height. Based on the apex height of the roof wedge (3.85 m), lower left wedge (3.32 m), and lower right wedge (2.59 m) we will use a bolt length of 5 meters to support these wedges. We are not concerned with the Floor Wedge in this tutorial since it is stable and does not require support. Adding a Bolt Pattern Now we will add a bolt pattern which covers the sides and roof of the excavation. To add a bolt pattern, select the Add Bolt Pattern option from the toolbar or the Support menu. Select: Support > Add Bolt Pattern You will see the Add Bolt Pattern on Perimeter dialog. Enter a bolt length of 5 meters. We will leave all other values at the default settings. Select OK. 3-3

4 Now we can add the bolt pattern graphically with the mouse, as follows: 1. First of all, notice that as you move the mouse cursor, a red cross-hair icon tracks along the opening section boundary, and follows the mouse movement. 2. Hover the mouse cursor over the lower right vertex of the opening section (the vertex at 277.5, 306). When the red cross-hair cursor is exactly on the vertex (it will automatically snap to the nearest vertex), click the left mouse button. This will define the starting point for the bolt pattern. 3. If you immediately see a bolt pattern around the entire opening section, don t worry, this is normal. Move the mouse in a counter-clockwise direction around the opening section boundary, and you will see the bolt pattern displayed as the mouse is moved. 4. Remember: a bolt pattern is always generated in a counter-clockwise direction around the opening section boundary. 5. When the red cross-hair cursor is at the lower left vertex of the boundary (the vertex at 264.5, 303), click the left mouse button again, and the bolt pattern will be added to the model as shown in the following figure. NOTE: If you make a mistake and create an incorrect pattern, don t worry just select Undo (from the toolbar or the Edit menu), and try again, repeating steps 2 to 5, until the bolt pattern looks like the figure below. NOTE: Figure 2 Bolt pattern applied to sides and roof of cavern. The spacing of the bolts along the boundary is 1.5 meters. This is the In-plane Spacing we used in the Add Bolt Pattern dialog. All bolts are normal (perpendicular) to the boundary segment on which they are located, since we used the Normal orientation option in the Add Bolt Pattern dialog. The bolt pattern begins exactly on the first point that you clicked on, but it will not necessarily end exactly on the second point (unless the distance between the two points is an exact multiple of the in-plane spacing). 3-4

5 Bolt Properties We will now discuss the properties of the bolts we have just installed. To define bolt properties, select Bolt Properties from the toolbar or the Support menu. Select: Support > Bolt Properties You will see the following dialog. For this tutorial, we will initially use the default bolt type and properties, which is a Mechanically Anchored bolt with a 0.1 MN capacity. Select Cancel in the Bolt Properties dialog. This bolt property type (Bolt Property 1) is already assigned to the bolt pattern (when we added the bolts with the Add Bolt Pattern dialog), so we do not need to assign the properties. Other bolt types available in Unwedge include Grouted Dowel, Cable Bolt, Split Set and Swellex. For complete details about how bolt properties are implemented in Unwedge, see the Unwedge help system. 3D Wedge View Now let s take a look at the model in the 3D Wedge View. Select 3D Wedge View from the drop-down menu on the toolbar or use the Select View sub-menu of the View menu: By default, only bolts which intersect the wedges are displayed. 3-5

6 Figure 3 Bolts displayed in 3D wedge view. 1. Maximize the perspective view by double-clicking in the view. 2. Use the mouse to rotate the model in the perspective view (click and drag with the left mouse button in the perspective view), and observe how the bolts intersect the wedges. 3. Click and drag on the wedges to move them away from the excavation. Note that the bolts remain in place, and do not move with the wedges. 4. Reset the wedges to their default position (select Reset Wedge Movement from the sidebar, or double click the middle mouse button). You can view ALL of the bolts generated in the pattern by selecting Bolt Visibility = All in the sidebar. However, bolts which do NOT intersect a wedge have no effect on the analysis, and do not affect the wedge safety factor in any way. 3-6

7 Look at the Wedge Info panel in the sidebar. The addition of the pattern bolt support has increased the wedge safety factor as follows. No Support Safety Factor Pattern Bolt Support Roof Wedge Lower Left Wedge Lower Right Wedge Table 1 Effect of pattern bolt support on safety factor. Reset the bolt visibility so that only the bolts which intersect the wedges are displayed. Select: Bolt Visibility = Intersecting Wedges. Bolt Data Tips Figure 4 Display of all bolts in pattern (Bolt Visibility = All). In the 3D Wedge View, bolt information can be displayed as popup data tips for individual bolts, by hovering the mouse over any bolt which intersects a wedge. This information includes the bolt property type, the length of the bolt which passes through the wedge (wedge length), anchorage length, failure mode, support force and bolt efficiency. This is shown in the following figure. Figure 5 Display of data tip for bolt results. 3-7

8 NOTE: if you do not see any Data Tips, make sure that Data Tips are enabled (select View > Data Tips > Maximum). For this example (mechanically anchored bolts), the bolt support force which is applied to the wedge is equal to the bolt tensile capacity (0.1 MN) multiplied by the bolt efficiency. The bolt efficiency is a factor which is used to account for the bolt orientation, and the fact that bolts may not be mobilized in pure tension. Bolt efficiency is a function of the bolt orientation relative to the direction of wedge movement. For complete details about how the bolt properties are used to determine the support force applied to a wedge, see the Unwedge help system. Restore the 4-view display by double clicking in the perspective view. Editing a Bolt Pattern The parameters of an existing bolt pattern can be easily edited with the Edit Bolt Pattern option. This allows you to change the bolt spacing, length, etc. NOTE: In the 3D Wedge View, the Edit Perimeter Bolt Pattern option is only available as a rightclick shortcut. In the Perimeter Support Designer View, the Edit Bolt Pattern option is available from the toolbar, from the Edit sub-menu of the Support menu, or right-click menu. Since we are currently viewing the 3D Wedge View, let s use the right-click shortcut method. 1. Right click on ANY bolt in the pattern, in ANY view (e.g. perspective, top, front or side view). 2. Select Edit Perimeter Bolt Pattern from the popup menu. 3. You will see the Edit Bolt Pattern on Perimeter dialog. Change the In Plane pattern spacing to 2 meters, and the Out of Plane pattern spacing to 2 meters. Select OK. Notice that the safety factor of all three wedges has decreased slightly. This is because the new pattern spacing has resulted in fewer bolts which intersect the wedges. Out of Plane Offset The Out of Plane Offset option in the Pattern Bolt dialog allows you to shift the origin of the bolt pattern in the direction of the tunnel axis. This can change the safety factor by changing the position and number of bolts which intersect a wedge. By default, the Out of Plane Offset is zero, which simply means that the origin of the bolt pattern is at z=0, which corresponds to the apex location of all perimeter wedges. Since the actual position of wedges is usually not known in advance, it is usually not possible to specify a meaningful value for the Out of Plane Offset. However, it does allow you to check the sensitivity of the wedge safety factor to changes in the longitudinal position of the pattern. Out of Plane Angle By default, all bolts that are part of a bolt pattern will lie in the x-y plane and thus will be orthogonal to the extrusion (z) direction. Both end points of the bolt will have the same z 3-8

9 coordinate. To angle the bolts out of plane (z direction), the Out of Plane Angle option is used. The angle is measured in a plane containing both the bolt and the z axis. The angle is measured from the bolt in the x-y plane (angle = 0). As an optional exercise: 1. Try different values of Out of Plane Offset and Out of Plane Angle in the Edit Bolt Pattern dialog, and observe the changes in safety factor. 2. Note: you can enter positive or negative values for the offset, so try values between -1 and +1 for example. If you select the Apply button in the dialog you can view the new results for each offset or angle value without closing the dialog. Observe the position of the bolt pattern and the values of safety factor for each offset value. Switch to 3D Wedge View to see the angle of the bolts. 3. In general, the safety factor will be maximized at some particular value of Out of Plane Offset or Out of Plane Angle. However, the optimal value of offset may be different for each wedge. 4. When you are finished, reset the Out of Plane Offset and Out of Plane Angle values to zero. TIP: The Out of Plane Offset option can also be useful if you want to apply more than one bolt pattern (e.g. to use different bolt types) and you want to offset the different patterns by a given distance. Editing Bolt Properties Now let s try a different type of bolt. Since we are viewing the 3D Wedge View, we will use the right-click shortcut to access the Bolt Properties dialog. 1. Right click on ANY bolt in the pattern, in ANY view (e.g. perspective, top, front or side view). 2. Select Bolt Properties from the popup menu. 3. In the Bolt Properties dialog, change the bolt type to Swellex. We will use the default properties for the Swellex bolt type, so just select OK. Notice that the safety factor of the 3 wedges has decreased. Although the swellex bolt tensile capacity (0.1 MN) is the same as the previous mechanically anchored bolt type, a swellex bolt can also fail by pullout or stripping at the ends of the bolt, if the bond strength or face plate capacity is exceeded. We will illustrate this by displaying the support force diagram for the bolts. Figure 6 Support force diagram for swellex bolt. 3-9

10 Bolt Support Force Diagram A bolt support force diagram in Unwedge displays the tensile support capacity along the length of the bolt (i.e. if a bolt intersects a wedge at a given point along the length of the bolt, what is the maximum possible tensile support force which can be supplied by the bolt). The support force diagram for bolts can be displayed in the 3D Wedge View as follows: 1. First, maximize the perspective view by double-clicking in the view. 2. Right-click on any bolt and select Support Force Diagram from the popup menu. 3. A representation of the support force diagram will now be displayed along the length of each bolt. Zoom in and rotate the model as desired, in order to see the support force diagrams (see Figure 7). 4. For the swellex bolts, note the 3 possible failure modes stripping, tensile failure, pullout. 5. The failure modes are represented by different colours: tensile (red), stripping (blue), pullout (green). After zooming and rotating your screen may look as follows. Figure 7 Display of bolt support force diagrams in perspective view. Other display options are available, for example: 1. Right-click on any bolt, and turn on the Bolt-Joint Intersection option (this will display a small marker at each bolt-wedge intersection). 2. Click and drag the roof wedge away from the excavation. Rotate the model as desired for better viewing of the intersection markers. 3. This graphically illustrates how the failure mode for each bolt (stripping, tensile, pullout) corresponds to the position of the wedge-bolt intersection point on the support force diagram. 3-10

11 For complete details about bolt support implementation and bolt support force diagrams, see the Unwedge help system. Reset the default viewing options (i.e. turn off the display of the bolt support force diagrams and bolt-joint intersections, reset the wedge position, select zoom all, and double-click in the perspective view to restore the 4-view display). Perimeter Support: Shotcrete Now let s add some shotcrete support to the cavern perimeter. First we have to switch back to the Perimeter Support Designer view using the drop-down menu on the toolbar or the Select View sub-menu of the View menu. The procedure for adding shotcrete to the perimeter is very similar to the method of adding a bolt pattern. Select the Add Shotcrete Layer option from the toolbar or the Support menu. Select: Support > Add Shotcrete Layer You will see the Add Shotcrete Layer dialog, which allows you to choose the shotcrete property type. We will use the default properties (Shotcrete Property 1), so just select OK. Now add the shotcrete layer graphically with the mouse, as follows: 1. First of all, notice that as you move the mouse cursor, a red cross-hair icon tracks along the opening section boundary, and follows the mouse movement. 2. Hover the mouse cursor over the lower right vertex of the opening section (the vertex at 277.5, 306). When the red cross-hair cursor is exactly on the vertex (it will automatically snap to the nearest vertex), click the left mouse button. This will define the starting point for the shotcrete layer. 3. If you immediately see the shotcrete layer around the entire opening section, don t worry, this is normal. Move the mouse in a counter-clockwise direction around the opening section boundary, and you will see the shotcrete layer displayed as the mouse is moved. The shotcrete layer is displayed as a narrow coloured strip along the inside of the opening section boundary. 4. Remember: a shotcrete layer is always generated in a counter-clockwise direction around the opening section boundary. 5. When the red cross-hair cursor is at the lower left vertex of the boundary (the vertex at 264.5, 303), click the left mouse button again, and the shotcrete layer will be added to the model as shown in the following figure. NOTE: If you make a mistake and create an incorrect layer, don t worry just select Undo (from the toolbar or the Edit menu), and try again, repeating steps 2 to 5, until your screen looks like the figure below. 3-11

12 Figure 8 Shotcrete layer added to perimeter of opening section Look at the Wedge Information panel in the sidebar, and you can see that the addition of the shotcrete layer has greatly increased the safety factor of the roof and side wedges. NOTE: Multiple layers of shotcrete can be added by repeating the above steps. The layers can be placed anywhere on the perimeter, and can overlap in any manner. Each layer can have different properties. It is left as an optional exercise to experiment with these options after completing this tutorial. Shotcrete Properties Properties of shotcrete are defined with the Shotcrete Properties option. Select Shotcrete Properties from the toolbar or the Support menu. Select: Support > Shotcrete Properties You will see the following dialog. 3-12

13 As you can see, the shotcrete properties are Shear Strength, Unit Weight and Thickness. We have used the default properties (a 10 cm thick layer with shear strength = 1 MPa). The Shear Strength of the shotcrete multiplied by the thickness determines the passive support force which can be generated by the shotcrete per unit length of wedge perimeter (i.e. the exposed perimeter of the wedge at the excavation face). The assumed shotcrete failure mode is direct shear. The Unit Weight of the shotcrete is used to determine the total weight of shotcrete which has been applied to the face of a wedge. The shotcrete weight is added to the wedge weight and included in the stability calculations. The shotcrete weight can noticeably affect the safety factor of a wedge, if the thickness of the layer is significant. NOTE: For more information about how the shotcrete support force is implemented in the wedge stability calculations, and the failure mode assumptions, see the Theory > Support > Shotcrete Support Force topic in the Unwedge help system. Let s define another shotcrete property type. This is done by selecting the Add button in the Shotcrete Properties dialog: Select the Add button once to create a new shotcrete property type. Enter Shear Strength = 0.5 MPa. Select OK. Editing a Shotcrete Layer Now let s assign the new shotcrete property type to the existing shotcrete layer. This can be done by selecting Edit Shotcrete Layer from the toolbar (left click in the layer, then right-click and select Done Selection). Or we can use the following right-click shortcut: 1. Right-click the mouse within the shotcrete layer which has been applied to the perimeter. Note: It may help to zoom in (rotate the mouse wheel forward) so that you can more easily click in the shotcrete layer. 2. Select Edit Layer from the popup menu. You will see the following dialog. Select Shotcrete Property 2 (i.e. the new shotcrete property type we defined) from the drop-list. Select OK. 3. The new shotcrete property type will now be applied to the perimeter shotcrete layer, as you will see from the colour of the shotcrete layer. The safety factor of the wedges has decreased, since the new shotcrete type has lower shear strength (0.5 MPa) than the previous shotcrete (1 MPa). The new shotcrete type could represent the shotcrete strength at an earlier age, for example. 3-13

14 TIP: If you hover the mouse over a shotcrete layer, you will see the properties of the layer displayed as a popup data tip. Display of Shotcrete in 3D Wedge View Finally let s see how shotcrete is displayed in the 3D Wedge View. Select 3D Wedge View from the drop-down menu on the toolbar or use the Select View sub-menu of the View menu. Double-click in the perspective view to maximize the view. As you can see, when shotcrete is applied to the excavation perimeter, it is displayed as semi-transparent shading on the perimeter where the shotcrete has been applied. The colour corresponds to the shotcrete colour defined in the Shotcrete Properties dialog. The display of shotcrete in the 3D wedge view can be turned on or off in the Display Options dialog under the Support tab. NOTE: If multiple layers of shotcrete have been applied, only the colour of the innermost layer of shotcrete will be displayed in the 3D wedge view. Figure 9 Display of shotcrete in 3D wedge view. That concludes this tutorial on how to model perimeter support using pattern bolts and shotcrete. 3-14