Tutorial 01 Quick Start Swedge

Quick Start Tutorial 1-1

Swedge v.6.0 Tutorial Manual

Quick Start Tutorial

Swedge is an interactive and simple to use analysis tool for evaluating the stability of surface wedges in rock slopes, defined by two intersecting discontinuity planes, the slope surface and an optional tension crack. This “quick start” tutorial will introduce you to the basic features of Swedge, and demonstrate how easily a model can be created and analyzed with Swedge.

The finished product of this tutorial can be found in the Tutorial 01 Quick Start.swd file, located in the Examples > Tutorials folder in your Swedge installation folder.

Topics Covered in this Tutorial

Project Settings Deterministic Analysis Input Data Wedge View Viewing Options Analysis Results Info Viewer Stereonet View Water Pressure External Force Seismic Force Sensitivity Analysis



Introduction

Swedge computes the factor of safety for translational slip of a tetrahedral wedge formed in a rock slope by:

two intersecting discontinuities (joint sets),

the slope face,

the upper ground surface, and

a tension crack (optional).

Typical problem geometry is illustrated below.

Figure 1: Typical wedge geometry for Swedge analysis.

When a pair of discontinuities are selected at random from a set of field data, it is not known whether:

the planes could form a wedge (the line of intersection may plunge too steeply to daylight in the slope face or it may be too flat to intersect the upper ground surface).

one of the planes overlies the other (this affects the calculation of the normal reactions on the plane).

LEGEND

1 , 2 = Failure planes (2 intersecting joint sets)

3 = Upper ground surface

4 = Slope face

5 = Tension crack

H1 = Slope height (vertical distance) referred to plane 1

L = Distance of tension crack from crest, measured along the trace of plane 1.



one of the planes lies to the right or the left of the other plane when viewed from the bottom of the slope.

In order to resolve these uncertainties, the solution has been derived using Block Theory, such that:

Either of the planes may be labeled 1 (or 2).

Allowance has been made for one of the planes overlying the other (this is illustrated in Figure 2)

The crest can overhang the base of the slope.

Contact may be lost on either plane (this is dependent on wedge geometry, and also on the magnitude of the water pressures acting on the planes).

A check on whether the two planes can form a wedge is included in the solution at an early stage. In addition, Swedge also examines how the tension crack intersects the other planes, accepting only those cases where the tension crack truncates the wedge in a kinematically admissible manner.

In all cases, the assumed failure mode of the wedge is translational slip — rotational slip and toppling are not taken into account.

Figure 2: Situation where wedge is formed, and one plane overlies the other.



Creating a New File

If you have not already done so, run the Swedge program by double-clicking on the Swedge icon in your installation folder. Or from the Start menu, select Programs Rocscience Swedge 6.0 Swedge.

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

When the Swedge program is started, a default model is automatically created, allowing you to begin defining your model immediately. If you do NOT see a wedge model on your screen:

Select: File New

Whenever a new file is created, the default input data will form a valid wedge, as shown in Figure 3.

NOTE: the automatic creation of a new file when Swedge is started, can be turned on or off in the Preferences dialog in the File menu.

Figure 3: Default wedge model.

Notice the four-view, split screen format of the display, which shows Top, Front, Side and Perspective views of the model. This 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.)



Project Settings

The Project Settings option allows you to configure the main analysis parameters for your model (i.e. Analysis Type, Units etc). Select Project Settings from the toolbar or the Analysis menu.

Select: Analysis Project Settings

You will see the Project Settings dialog.

Figure 4: Project Settings dialog.

Analysis Type

There are three main Analysis Types in Swedge – Deterministic, Probabilistic or Combinations. By default a Deterministic Analysis will be selected for a new file.

A Deterministic analysis assumes that all input parameters are “exactly” known. Swedge computes the factor of safety for a single wedge. Deterministic analysis will be demonstrated in this tutorial.



For a Probabilistic analysis, statistical input data can be entered to account for uncertainty in joint orientation and strength values. This results in a safety factor distribution, from which a probability of failure is calculated. Probabilistic analysis will be demonstrated in Tutorial 02.

For a Combination analysis, any number of discrete joint orientations can be defined, and Swedge will analyze all possible combinations of two joints. Combination analysis will be demonstrated in Tutorial 03.

Units

For this tutorial we will be using Metric (MPa) units, so make sure the Metric, stress as MPa option is selected for Units.

NOTE: the most recently selected Units option automatically becomes the default for all new files, so you do not have to select the Units each time you start a project. Make sure you are working in the correct units!

Sampling and Random Numbers

These options are only applicable for a Probabilistic Analysis, and will be discussed in the next tutorial.

Project Summary

Select the Project Summary tab in the Project Settings dialog.

Enter “Swedge Quick Start Tutorial” as the Project Title.

NOTE:

The Project Summary information can be displayed on printouts of analysis results, using the Page Setup option in the File menu and defining a Header and/or Footer.



You can specify the Author and Company in the Preferences dialog in the File menu, so that this information always appears by default in the Project Summary in Project Settings, for new files.

Select OK to close the Project Settings dialog.

Input Data

The Input Data option is the main input data dialog for Swedge. Let’s see what input data is used for the default Swedge model.

Select: Analysis Input Data

Figure 5: Input Data dialog (Deterministic) – slope properties.

For a Deterministic analysis, the Input Data dialog is organized under three tabs – Slope, Joints, Forces.

Examine the Slope properties input data. The slope plane orientations, slope height and rock unit weight is always required data. Other slope input data is optional. Do not change any values just yet, we will be coming back to this shortly.

Select the Joints tab in the Input Data dialog and examine the Joint information. There are three strength models available for defining the shear strength of joints – Mohr- Coulomb, Barton-Bandis and Power Curve. By default the Mohr-Coulomb strength model is selected.



TIP: you can minimize or maximize the Input Data dialog, without closing it, by double-clicking on the title bar at the top of the dialog, or selecting the arrow icon in the upper right corner.

Figure 6: Input Data dialog (Deterministic) – joint properties.

Select the Forces tab in the Input Data dialog. The Forces options allow you to apply Water Pressure, Seismic or External Forces. We will be demonstrating these options later in the tutorial.

NOTE: for detailed information about all Swedge input data options, see the Swedge help system. To access the Help system, you can select the question mark “?” icon in a dialog for context sensitive help. Or you can select Help > Help Topics from the Swedge menu.

Select Cancel to close the Input Data dialog.



Analysis Results

The Swedge analysis is automatically computed:

when a file is opened, or

when input data is entered or modified in a dialog (e.g. Input Data), and Apply or OK is selected in the dialog.

This ensures that the latest analysis results are always displayed.

The primary result from an Swedge Deterministic analysis is the wedge Factor of Safety (FS). This is displayed and in the sidebar information panel, as well as at the top of the Perspective View. If any view is maximized, the Factor of Safety will appear at the top.

Wedge Information Panel

The Sidebar in Swedge is the vertical panel at the right side of the Swedge application window. The Sidebar displays a summary of analysis results in the Wedge Information Panel.



Figure 7: Sidebar wedge information panel.

The information displayed in the Wedge Information Panel can be customized by selecting the Filter List button in the Sidebar, and choosing the desired data using the checkboxes in the Wedge Information Filter dialog. This is left as an optional exercise.



Figure 8: Wedge information filter dialog.

TIP: if you right-click in the wedge information panel the data can be copied to the clipboard with the right-click Copy shortcut.



Info Viewer

A comprehensive listing of input data and analysis results is presented in the Swedge Info Viewer.

To access the Info Viewer, select the Info Viewer option from the toolbar or the Analysis menu.

Select: Analysis Info Viewer

Figure 9: Info Viewer summary of analysis information.

Use the scroll bar or the mouse wheel to scroll down and view all of the data in the Info Viewer.

The Info Viewer data can be copied to the clipboard or saved to a file using the options in the right-click popup menu. This is left as an optional exercise.

Close the Info Viewer by selecting the X in the upper right corner of the view.



Stereonet View

The Stereonet View in Swedge displays a stereographic projection of your Input Data plane orientations (slope, upper face, joint1, joint2, tension crack).

To access the Stereonet view, select the Stereonet option from the toolbar or the Analysis menu.

Select: Analysis Stereonet

Figure 10: Stereonet view of input data planes.

By default, the Stereonet is displayed using Equal Angle projection. Equal Area projection can also be used. If you right-click on the Stereonet view, you can change the projection method and other stereonet display options (e.g. Show Planes, Show Poles, Show Intersections, Show Failed).

The Stereonet display options are also available in the Stereonet sub-menu of the View menu, and in the Display Options dialog.



Viewing Options

Switch back to the Wedge View by selecting the Wedge View option from the toolbar or the Analysis menu.

Select: Analysis Wedge View

We will now discuss some of the viewing options and shortcuts for the Wedge View.

Rotating the Model

Within the Perspective view, the Swedge model can be rotated for viewing at any angle, interactively with the left mouse button, as follows:

1. Press and hold the left mouse button anywhere in the Perspective view. Notice that the cursor changes to a "circular arrow" symbol

to indicate that you may rotate the model.

2. Keep the left mouse button pressed, and move the cursor around. The model is rotated according to the direction of movement of the cursor.

3. To exit the rotation mode, release the left mouse button. The cursor reverts to the normal arrow cursor.

To reset the rotation to the default viewing angle, select Reset View from the right-click menu or the View menu.

Figure 11: Rotation of slope model in Perspective view.

Moving the Wedge

The wedge can be moved out of the slope by clicking and dragging with the left mouse button, or by rotating the mouse wheel, as described below.

To move the wedge with the left mouse button:

1. Position the cursor over the wedge in the Perspective, Top or Front views of the model.



2. The cursor will change to a vertical, two-way arrow symbol . Click and hold the left mouse button, and drag the mouse. As you move the cursor up or down, the wedge will slide up or down out of the slope, along the direction of sliding.

Figure 12: Wedge moved along sliding direction.

The wedge can also be moved by rotating the mouse wheel while holding down the Shift or Ctrl keys on the keyboard:

1. If you hold down the Shift key and rotate the mouse wheel, the wedge movement will be larger.

2. If you hold down the Ctrl key and rotate the mouse wheel, the wedge movement will be smaller.

3. Rotating the mouse wheel forward moves the wedge upwards. Rotating the mouse wheel backward moves the wedge down.

Reset Wedge Movement

To reset the wedge to its default position, you can:

double click the mouse wheel in any view, or

select Reset Wedge Movement or Reset View from the right-click menu.

Any of these options will reset the wedge to its default position within the slope.



Re-sizing the Views

You can change the relative size of the panes or sub-views (Top / Front / Side / Perspective), or maximize any view within the Wedge View.

To maximize the size of any pane, double-click the left mouse button in the pane (e.g. double-click in the Perspective view to maximize the Perspective view). Double-clicking again in the maximized view will restore the default display of all 4 panes.

You can also re-size the 4-view display by clicking and dragging on the vertical or horizontal dividers between the panes.

TIP: if you have re-sized the panes and you want to quickly restore the default display, double-click in any pane to maximize the view, then double-click again to restore the default display.

Figure 13: Maximized perspective view.



Zoom and Pan

The following Zoom and Pan options are available for the Wedge View:

Zoom All – reset the model to its default size and location in the view

Zoom In – zoom in to 90 % of the original area

Zoom Out – zoom out to 111% of the original area

Pan – translate the model left, right, up or down within the view

The zoom and pan options are available in the toolbar, the Zoom sub-menu of the View menu, and through various keyboard and mouse shortcuts. Shortcuts include:

Rotate the mouse wheel forward or backward to zoom in or out.

The function keys F2, F4 and F5 are shortcuts to Zoom Extents, Zoom Out and Zoom In respectively.

A shortcut to Pan is to click and hold the middle mouse button (mouse wheel) and drag to pan the model within the view.

For additional shortcuts see the Zoom and Pan topic in the Swedge Help system.



Changing Input Data

Now let’s enter data for a different wedge.

Select: Analysis Input Data

Select the Slope tab in the Input Data dialog and enter the following data.

Slope Height 20

Slope Dip 65

Slope Dip Direction 45

Upper Face Dip 10

Upper Face Dip Direction 45

Unit Weight (MN/m3) 0.027



Select the Joints tab in the Input Data dialog and enter the following data.

Joint 1 Dip 45

Joint 1 Dip Direction 52

Joint 1 Cohesion (MPa) 0.025

Joint 1 Friction Angle 30

Joint 2 Dip 70

Joint 2 Dip Direction 18

Joint 2 Cohesion (MPa) 0

Joint 2 Friction Angle 35

NOTE: the Joint Waviness angle accounts for the waviness (undulations) of a joint surface, observed over distances on the order of 1 m to 10 m, and has the effect of increasing the shear strength of the joint. For more information see the Swedge Help system. We will leave the Waviness angle = 0 for this example.

Select OK in the Input Data dialog to re-compute the Swedge analysis with the new input data. You should see the following wedge, with a Safety Factor of approximately 1.11.



Figure 14: Wedge formed by new input data.

Sliding Plane

Notice that the analysis summary in the Sidebar indicates the failure mode as Sliding on Joint 1. Due to the geometry of this wedge, the failure mode is sliding on one joint, rather than sliding on both joints (i.e. along the line of intersection of joints 1 and 2.)

This is consistent with the wedge geometry, since Joint Set 2 dips at 70 degrees and has a cohesion of zero, and therefore has little influence on the wedge stability.

Figure 15: Failure mode – sliding on Joint 1.



Water Pressure

By default, Water Pressure is NOT applied to an Swedge model, and the analysis is therefore applicable to a DRY slope.

To include Water Pressure in a Deterministic analysis:

1. Select Input Data. Select the Forces tab in the Input Data dialog, and select the Water Pressure checkbox.

2. Select the Water Pressure Type (we will use the Filled Fissures option for this example, with default Hu=1).

3. Select OK. The Safety Factor decreases to 0.57, indicating an unstable wedge. The Filled Fissures option assumes extreme conditions of heavy rainfall, such that maximum (average) values of water pressure are applied on the failure planes.

Notice that arrows representing the Water Pressure force are displayed normal to the wedge failure planes.

Figure 16: Display of water forces on joint planes (side view).



In the Sidebar information panel, note the values of (effective) Normal Force, Normal Stress and Shear Strength for Joint1. The application of the Water Pressure has reduced these values, compared to the dry state, resulting in the decreased safety factor.

External Force

Now let’s add a single External Force, in a direction such that it will help to stabilize the wedge.

1. Select Input Data. Use the mouse to select Number of External Forces = 1.

2. Enter Trend = 225, Plunge = 20 and Magnitude = 10 MN.

3. Select OK. The Safety Factor (with Water Pressure still applied) increases to 0.73 (still an unstable wedge).

An arrow representing the External Force is now displayed on the model. (External force can also be applied to a model by adding support. See the Support Tutorial for details.)



Figure 17: Display of water and external forces on wedge (side view).

NOTE: the force arrows which are displayed, represent the presence and direction of an external force, but do NOT represent the magnitude (i.e. the size of the arrows is NOT proportional to force magnitude.)

Seismic Force

Now we will include Seismic Force in the analysis.

1. Select Input Data, and select the Seismic checkbox.

2. Enter a Seismic Coefficient of 0.2. Select the Direction = User Defined and enter Plunge = 0 and Trend = 52.

3. Select OK. The Safety Factor drops to 0.50.

An arrow representing the Seismic Force is now displayed on the model.

Figure 18: Display of water, external and seismic forces on wedge (side view).



The Seismic Force applied to the wedge is F = 0.2 * g * m, where g = acceleration due to gravity and m = mass of the wedge. Note that the Trend is equal to the Dip Direction of Joint Set 1, which is the worst possible direction in this case, since the failure mode for this wedge already indicates Sliding on Joint 1.

Sensitivity Analysis

Before we conclude this tutorial, we will demonstrate the Sensitivity Analysis feature of Swedge.

In a Sensitivity Analysis, individual variables can be varied between user defined minimum and maximum values, while all other input parameters are constant. This allows you to determine the effect of individual variables on safety factor.

We will use Sensitivity Analysis to show that the worst possible direction to apply a Seismic Force, is the sliding direction of the wedge.

1. Select Input Data and turn OFF the Water Pressure by clearing the Water Pressure checkbox. Also turn OFF the External force, by setting Number of External Forces = 0. Only the Seismic force checkbox should remain selected. Select OK.

2. Select the Sensitivity Analysis option from the toolbar or the Analysis menu.

3. In the Sensitivity Input dialog, select the first checkbox at the upper left, and select Seismic Force Trend from the drop-list of variables. Enter From = 0 and To = 120. Select OK.



4. You should see the following sensitivity plot.

Figure 19: Sensitivity plot of seismic force trend versus safety factor.



As you can clearly see from the graph, the minimum factor of safety occurs when Seismic Force Trend = 52 degrees, which is the wedge failure direction (and the Dip Direction of Joint 1).

Although the wedge failure direction is often the most critical direction in which to apply a seismic force, this may vary depending on the presence of other external forces (e.g. water pressure, support etc) and the strength properties of the individual failure planes.

It is left as an optional exercise to explore the effect of Seismic Force Plunge on the safety factor, using the Sensitivity Analysis option.

That concludes this quick start tutorial.

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Tutorial 01 Quick Start Swedge

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