Swedge 5.0New Analysis Optionsand Improvements

Article prepared by Rocscience Inc. - RocNews Spring 2006

Swedge 5.0 – new analysis options and more... Swedge is an interactive analysis tool for evaluating the geometry and stability of surface wedges in rock slopes. Wedges are defined by two intersecting discontinuity planes, the slope surface and an optional tension crack. Analysis types include Deterministic, Probabilistic, Combinations, Sensitivity, and Persistence analysis. Rock bolts, shotcrete or support pressure can be applied to increase the wedge safety factor. De-stabilizing forces due to water pressure, seismic loads or external forces can also be modeled. Rocscience is pleased to announce the release of Swedge version 5.0, a major upgrade which offers significant new analysis options and improvements. Here is a list of the major new features you will find in Swedge 5.0 and described in detail in this article.

Combination Analysis Import from Dips Sensitivity Analysis Persistence Analysis Joint Shear Strength Statistical Distributions Wedge Size Stereonet View User Interface Report Generation New Analysis Engine

Typical Swedge model (perspective, top, front and side views)

Combination Analysis The new Combination Analysis option in Swedge allows you to enter any number of discrete joint plane orientations, and all possible combinations of two joints which can form a wedge will be analyzed. The wedge with the minimum factor of safety is determined, and results can be plotted on histograms, scatter plots and the stereonet view. The joint orientation data can be entered or copied directly into Swedge or imported from a Dips file (see below). You may define a single set of orientation data or two sets. If two sets are defined, then the two sets can have different strength properties, and all possible combinations (using one joint from each set), will be analyzed.

Combination analysis selected in Project Settings

Joint orientations imported from Dips file for Combination analysis

Stereonet view of Combination analysis results, showing joint intersections

Distribution of wedge safety factor after a Combination analysis

Import from Dips Dips is a Rocscience program for the graphical and statistical analysis of structural geology data using stereonets. Dips and Swedge are commonly used together for the analysis of rock slope stability (e.g. Dips can be used to determine mean joint set orientations, and these values are entered into Swedge). In previous versions of Swedge, it was possible to import only mean plane orientations from Dips. Due to customer demand, the following new options are available for importing Dips data into Swedge:

Import All Orientations (Combination Analysis) A complete Dips file can now be imported into Swedge, and analyzed with the Combination analysis option (see above). All possible combinations of two joints which can form a wedge will be analyzed. Import Joint Set Statistics (Probabilistic Analysis) If you are using the Probabilistic analysis option, you can import joint set statistics (mean orientation and Fisher Distribution K value or standard deviation) from a Dips .DWP file into Swedge.

Joint set statistics can be imported from a Dips .DWP file

Sensitivity Analysis Sensitivity analysis is a new feature in Swedge 5.0, which allows you to quickly determine the effect of individual variables on wedge safety factor. In a Sensitivity analysis, an individual variable is varied between user defined minimum and maximum values, while all other input parameters are constant. This allows you to determine which variables have the most effect on safety factor, and which variables have little or no effect on safety factor.

Input dialog for sensitivity analysis The results of a Sensitivity analysis are displayed on a Sensitivity plot as shown below.

Sensitivity analysis plot of 3 variables

Joint Persistence Analysis Joint Persistence analysis is a new feature in Swedge which allows you to define statistical distributions for joint persistence. For a given wedge size, randomly generated values of persistence are used as a filter to determine if a wedge can actually form. If the wedge dimensions exceed the allowable persistence, then the wedge cannot exist. If the wedge dimensions are smaller than the allowable persistence, then the wedge can form and a safety factor is calculated. This process is repeated for the specified number of random trial samples. The persistence analysis can be applied to the maximum wedge size, or to a randomly generated wedge size. The random variation of wedge size simulates the random variation of the wedge location (i.e. the intersection of two joint planes may daylight anywhere on a slope face).

Input dialog for Persistence analysis The Persistence analysis option is a refinement to the Swedge Probabilistic analysis. It can be used on its own, or simultaneously with any other Probabilistic analysis options in Swedge (i.e. you can define any other input random variables, in addition to the joint persistence). In general, by checking for allowable joint persistence in a probabilistic analysis, this can only DECREASE the calculated probability of failure. The Persistence analysis option should give more realistic estimates of probability of failure for slopes where the joint planes are not continuous.

Joint Shear Strength In addition to the Mohr-Coulomb criterion, Swedge now offers the Barton-Bandis and Power Curve strength models for modeling the shear strength of joints. For all strength criteria, a waviness angle can also be defined. The waviness angle models the effect of waviness or undulations of joint surfaces on the scale of approximately 1 to 10 meters, and has the effect of increasing the shear strength of a joint.

New modeling options for joint shear strength A new strength modeling option for Probabilistic analysis, is the ability to directly define the joint shear strength as a random variable. That is, instead of defining statistical distributions for individual strength parameters (e.g. cohesion and friction angle), you can define a single statistical distribution which is applied to the mean strength envelope. This is a more intuitive method of modeling the variability of shear strength. This option is particularly useful for Barton-Bandis or Power Curve strength models, since it eliminates the need for defining statistical distributions for individual strength parameters (which may be difficult to obtain or unavailable). Furthermore, the issue of statistical correlation of the strength parameters is avoided (i.e. you do not have to worry about generating unrealistic combinations of strength parameters, since variability is defined with respect to the mean envelope).

Random shear strength option (Mohr-Coulomb)

Shear strength variability around mean envelope

Statistical Distributions Two important statistical distributions have been added to the list of available distributions for defining random variables for an Swedge Probabilistic analysis:

• Fisher Distribution • Gamma Distribution

Fisher Distribution A Fisher distribution is commonly used to define a symmetric, 3-dimensional distribution of orientation vectors (e.g. pole vectors representing a joint set). In Swedge, a Fisher distribution can be used to define joint or tension crack orientation as random variables. One advantage of using a Fisher distribution is that it is not necessary to define independent distributions for Dip and Dip Direction, only a single parameter (standard deviation or Fisher K value) defines the variability of the distribution around the mean. Fisher statistics can also be imported from a Dips file as described earlier in this document.

Fisher distribution used to generate random joint orientations Gamma Distribution The Gamma distribution is widely used in geotechnical engineering to model continuous variables that are always positive and have skewed distributions. In Swedge, the Gamma distribution can be useful for variables such as cohesion or shear strength for example.

Wedge Size Options Various improvements have been made in the capability for defining or limiting the size of wedges in Swedge. These are described below.

Slope Length The slope length option allows you to limit the size of wedges according to the length of the slope. This is particularly useful for Probabilistic or Combination analysis. In previous versions of Swedge there was no limitation on length, which could lead to unrealistically long wedges being generated.

Slope length option Minimum Wedge Size For Probabilistic or Combination analysis, it is now possible to define a minimum wedge size. This prevents the computation of extremely small wedges which can be generated by the analysis, and which can interfere with the determination of larger critical wedges which are much more significant.

Minimum wedge size option

Scaling The Scale Wedges option has been improved. The scaling dialog is easier to use (checkboxes allow you to select only the desired parameters), and the scaling information (e.g. trace length, persistence) is now saved with the file. Scaling now works with Probabilistic or Combination analysis (previously scaling only worked with Deterministic analysis).

Improved Scale Wedges dialog Persistence Analysis The Persistence analysis option, described earlier in this document, is another method of accounting for wedge size in the analysis, and allows a random variation of wedge height to simulate the random location of joint intersections on a slope face.

Stereonet View The Stereonet view in Swedge has been improved as follows:

• You can now view ALL poles for all orientations used in the analysis (e.g. all randomly generated poles for a Probabilistic analysis, or all joint poles for a Combination analysis)

• Joint intersections are now plotted on the stereonet view (i.e. the line of intersection of Joint1 and Joint2 for all valid wedges generated by the analysis).

• The poles and intersections corresponding to FAILED wedges can be highlighted on the stereonet, as seen in the following figure (failed poles/intersections are highlighted in red).

Right-click menu for stereonet view

Stereonet view showing random joint set orientations and intersections

Improved User Interface Several improvements have been made to the Swedge user interface. The most obvious change is the new Sidebar information panel, which displays a summary of analysis results and input data at the side of the screen. The information which is displayed can be customized with the Filter List option.

Sidebar information panel Other improvements include:

• Improved options for graphical manipulation of the wedge view with the mouse (e.g. moving the wedge, zooming and panning)

• Improved right-click menus • Improved Info Viewer • General improvements to dialogs, menus etc. • Customizable header / footer information for printouts

Report Generation Swedge 5.0 offers new and improved features which facilitate the creation of professional looking reports and presentations, after you have completed the analysis. This includes:

• Improved printing, including a new option for applying customized header / footer information to printouts

• Improved Info Viewer layout with customizable fonts, decimal places etc. • New sidebar information panel

Printing

In the Page Setup option in the File menu, you can apply customized header and/or footer information to printouts of any Swedge view. You can choose from pre-defined templates, or create your own header / footer design, and include your company logo.

Customizable title block can be applied to printouts

Footer information in print preview mode

Headers / footers can be customized for each Swedge view if desired (e.g. Wedge View, Info Viewer, Stereonet, Charts etc.).

NOTE: the entire Wedge View is now printed as you see it on the screen (e.g. all four views – Perspective, Top, Front, Side). Previously only the current pane within the Wedge View was printed (e.g. a single view such as Perspective).

Info Viewer

The layout of the Swedge Info Viewer has been improved (e.g. data is displayed in tables when appropriate), and the appearance is customizable (e.g. fonts, colours, decimal places etc), as configured in the Display Options dialog.

Improved Info Viewer layout

Sidebar information panel As discussed in the previous section, Swedge also displays a summary of analysis information in the Sidebar information panel. The sidebar information can easily be copied to the clipboard for including in reports.

New Analysis Engine Last but not least, Swedge 5.0 uses a completely new analysis engine based on Goodman and Shi’s block theory. The generalized nature of the block theory approach can determine if a removable wedge exists for any set of input orientations, and provides reliable solutions under a wide variety of modeling circumstances. The new engine handles cases which could not be analyzed with the previous Swedge analysis algorithm. It is also consistent with the Unwedge version 3.0 analysis engine. (Unwedge is a Rocscience program for wedge analysis around underground excavations). Conclusion Swedge 5.0 is a significant upgrade which should be considered by all users of Swedge 4.0 or earlier versions. For information on upgrade pricing or demo versions, contact Rocscience at software@rocscience.com