Tutorial_02_Scaling_Wedge_Size

Scaling Wedges TutorialUnwedge always initially calculates the maximum sized wedges which can form around an excavation.This tutorial demonstrates how to scale down the size of the wedges, to represent the actual size of wedges observed in the field. This is donewith the Scale Wedges option, which allows you to scale the size of wedges according to field measurements such as joint trace lengths, joint persistence, wedge face area etc.Wedge scaling is important because the assumed wedge size can have a significant effect on support requirements (e.g. pattern spacing, positioning or orientation of bolts, and the thickness or strength of shotcrete).The model represents a section of an underground spiral access ramp.Topics Covered•Scaling Wedge Size•Scaling All Wedges•Scaling Individual Wedges•Safety factor and ScalingModelFor this tutorial we will start by reading in the file Tutorial 02 ScalingWedges.weg which you should find in the Examples > Tutorials folder inyour Unwedge installation folder.Select: File → OpenNavigate to the Examples > Tutorials folder in your Unwedge installationfolder and open the Tutorial 02 Scaling Wedges.weg file.The model should appear as follows.Figure 1: Maximum sized perimeter wedges for tutorial 2 example.As you can see, all of the Perimeter Wedges (roof, sides and floor wedges)are the maximum possible size for the excavation cross-section.NOTE: the Plunge of the Tunnel Axis Orientation is 15 degrees, becausethe model represents a section of an inclined ramp, rather than ahorizontal tunnel.Scaling WedgesTo scale down the size of wedges, select the Scale Wedges option fromthe Analysis menu.Select: Analysis → Scale WedgesYou will see the Scale Wedges dialog.Wedge size can be scaled according to joint trace length, joint persistenceor wedge data (e.g. volume, face area etc). Although we can entermultiple scaling parameters at the same time, let’s enter parameters oneat a time, to see the results at each step.Select the Joint 1 (Trace Length) checkbox, and enter a Scaling Value of 4meters. Select OK.Your screen should look as follows.Figure 2: Wedge size scaled by Joint 1 trace length = 4 meters.Notice that all of the wedges have been scaled down in size. To indicate that scaling has been applied to a wedge, the letter “s” is displayed beside the wedge number (e.g. the roof wedge is numbered “8s”). NOTE: if you do not see the wedge numbers, go to Display Options, select the Wedge View tab, and make sure the Wedge Numbers checkbox is selected.Before we proceed further, select the Filter List button in the Sidebar.1.In the Wedge Information Filter dialog, select the Defaultsbutton (so that only the Wedge Name, Factor of Safety andWedge Weight checkboxes are selected).2.Now select the Scaled By checkbox and the Joint TraceLengths checkbox, as shown in the following figure. Select OK.Now look at the Wedge Information panel in the Sidebar. NOTE: •For all wedges, Scaled By = Joint 1 Trace Length•For all wedges, Joint 1 Trace Length = 4 meters.This is consistent with the single scaling value which we entered in the Scale Wedges dialog (Joint 1 Trace Length = 4 meters).At this point, we should note the following:•When we use the All Wedges scaling option (in the Scale Wedges dialog), this does not necessarily mean that all wedges will bescaled (i.e. reduced in size). It means that all wedges will beCONSIDERED for scaling. Wedges will only be scaled if theircurrent dimensions are larger than one of the scaling parameters.If the parameters of a wedge are already smaller than the scalingparameters, then the wedge will not be affected by the scaling.In the current example, all of the wedges were reduced in size, but ingeneral this will not necessarily be the case.Figure 3: Wedge information after scaling by Joint 1 trace length.Now let’s enter one more scaling parameter.Select: Analysis → Scale WedgesIn the Scale Wedges dialog, select the Joint 2 (Trace Length) checkbox, and enter a Scaling Value of 4 meters. Select OK.Look at the Wedge Information panel in the Sidebar. The results are now as follows:•For the Floor Wedge and the Roof Wedge, Scaled By = Joint 2 Trace Length, and Joint 2 Trace Length = 4 meters.•For the Lower Left and Lower Right wedges, Scaled By = Joint1 Trace Length, and Joint 1 Trace Length = 4 meters.For the Floor and Roof wedges, the Joint 2 trace length (scaling value) is now the governing parameter (the Joint 1 trace length is less than 4 meters).For the Lower Left and Lower Right wedges, the Joint 1 trace length (scaling value) is still the governing parameter, since the Joint 2 trace lengths are already less than 4 meters, therefore the Joint 2 trace length scaling value does not affect these wedges.This illustrates the following important points:•When you enter more than one Scaling Value, a given wedge is ultimately scaled by only one parameter – the parameter whichgives the smallest wedge size.•Furthermore, if Wedges to Scale = All Wedges (in the Scale Wedges dialog), and you have entered multiple scaling values, thegoverning scaling parameter can be different for different wedges. Let’s enter a third scaling parameter.Select: Analysis → Scale WedgesIn the Scale Wedges dialog, select the Joint 3 (Trace Length) checkbox, and enter a Scaling Value of 4 meters. Select OK.Look at the Wedge Information panel in the Sidebar:•For all wedges, Scaled By = Joint 3 Trace Length•For all wedges, Joint 3 Trace Length = 4 meters.The Joint 3 Trace Length scaling value (4 meters) is now the governing scaling parameter for all wedges. Notice that the actual Joint 1 and Joint 2 trace lengths for all wedges are now less than 4 meters.Figure 4: Wedge size scaled by Joint 3 trace length = 4 meters.NOTE: if you go back to the Scale Wedges dialog, and turn OFF the checkboxes for Joint 1 Trace Length and Joint 2 Trace Length, and select OK, the results will not change, since the Joint 3 Trace Length scaling value gives the smallest wedge size for all perimeter wedges.Position of Scaled WedgesFor perimeter wedges which span multiple segments of the Opening Section (e.g. the Roof wedge in this example), Unwedge uses an algorithm which searches for the wedge with the maximum volume for the given Scaling Value(s). An iterative process is required to find this wedge. This determines the position of the scaled wedge on the perimeter.In this example, if you compare Figure 2 and Figure 4, notice that the Roof Wedge is off to one side in Figure 2 and is approximately centered in Figure 4. The different positions of the Roof Wedge are due to the Unwedge searching algorithm and the different scaling values used for each case.For wedges which are formed on a single flat surface of the excavation boundary, the searching algorithm is not applicable, and the scaledwedge position will be approximately centered on the surface.Scaling Individual WedgesSo far in this tutorial, we have considered all wedges for scaling, using the same set of scaling values (i.e. in the Scale Wedges dialog, the Wedge to Scale option was set to All Wedges).It is also possible to consider individual wedges for scaling. This allows you to enter independent scaling values for any desired wedge(s). To select individual wedges for scaling:•You can select the desired wedge from the Wedge to Scale drop-list in the Scale Wedges dialog.•You can also right-click directly on a wedge, and select Scale Wedge for that particular wedge from the popup menu, as shownin the following figure. This will display the Scale Wedges dialogwith the wedge already selected in the dialog.For example:1.Right-click on the Roof Wedge, and select Scale Wedge: 8 Rooffrom the popup menu, as shown in the above figure.2.In the Scale Wedges dialog, select the Joint 2 Trace Lengthcheckbox and enter a scaling value of 3 meters. Select OK.3.Now look at the Wedge Information panel. The Roof wedge is nowscaled by the Joint 2 Trace Length = 3 meters. All other wedgesare still scaled according to the Joint 3 Trace Length scalingvalue entered with the All Wedges scaling option.Figure 5: Roof wedge scaled independently using Joint 2 Trace Length = 3.You can scale any or all wedges individually, in this manner. When you select individual wedges to scale, the Scaling Value parameters are entered independently for each wedge, and the dialog will “remember” the Scaling Values you have entered for each wedge.NOTE: if you specify Scaling Values for All Wedges, AND for individual wedges, at the same time in the Scale Wedges dialog, the program will use the Scaling Value which gives the smallest wedge, for any given wedge.Resetting the Maximum Wedge SizeTo reset all wedges to the maximum size, select the Maximize button in the Scale Wedges dialog. This will clear all of the Scaling Values, for All Wedges and also for any individual wedge Scaling Values you have entered.Scaling Wedges Tutorial 2-11 Unwedge v.3.0 Tutorial Manual Safety Factor and ScalingWe will now briefly discuss the effect of scaling the wedge size on the wedge safety factor and support requirements. Effect of Joint Strength• Frictional Strength Only – if the shear strength of the joint planes is purely frictional (cohesion = 0), then changing the size of an unsupported wedge will NOT change the safety factor. You can verify this for the current example (the Joint Shear Strength of all joints is given by Phi = 30 degrees, cohesion = 0).• Friction and Cohesion – if the shear strength of the joint planes includes a non-zero cohesion, then the safety factor of a wedge will, in general, depend on the size of the wedge.•Other parameters – water pressure, field stress and other parameters can also influence the dependence of wedge size and safety factor. SupportIf support has been applied to a wedge (e.g. bolts or shotcrete), then in general, changing the size of a wedge will affect the safety factor. This can be due to several factors:• The wedge size may affect the number of bolts which intersect a wedge (pattern bolting).• The wedge size will affect the relative embedded lengths of a bolt. For a bonded bolt, the length which passes through the wedge, and the length embedded in the rock mass will determine the support force applied to the wedge.•If shotcrete has been applied, then the wedge size will have a direct effect on the exposed perimeter length of the wedge face. This has a direct effect on the support force which is applied by the shotcrete. In conclusion, wedge scaling is of particular importance during support design, since the assumed wedge size can have a significant effect on the pattern spacing, positioning or orientation of bolts, and the thickness or strength of shotcrete.Wedge support is discussed in the next tutorial. That concludes thistutorial on scaling wedge size in Unwedge .。