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Combination Analysis
The Combination Analysis option in Swedge allows you to define 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 as shown below.
For example: if 100 joint orientations were defined, the number of potential joint combinations analyzed would be (100*99)/2 = 4950.
Combination analysis results (minimum wedge, stereonet and charts)
The Combination Analysis option can be selected in the Project Settings dialog or from the drop-list in the toolbar.
Combination Analysis selected in Project Settings
Combination Analysis selected in toolbar
By default, the minimum wedge Factor of Safety (FS) is displayed in the toolbar.
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Combination Analysis: Input Data
The Input Data dialog for a Combination Analysis is organized under 3 tabs - Slope, Joints, and Forces. The distinguishing feature of a Combination Analysis is the ability to enter any number of discrete joint plane orientations. The orientations can be entered into the spreadsheet in the Input Data dialog or imported from a Dips file. It is assumed that all joints have the same strength parameters, and you may choose from Mohr-Coulomb, Barton-Bandis or Power Curve models.
Combination analysis joint input data
It is also possible to define TWO distinct joint sets for a Combination Analysis, by selecting the Use Two Joint Sets checkbox. In this case, Swedge will compute all possible combinations of two joints, using one joint from each set, and you can define different strength properties for the two joint sets.
Combination analysis, defining a second joint set
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Combination Analysis: Minimum Factor of Safety
The main result from an Swedge Combination analysis, is the Minimum Factor of Safety Wedge. This is the wedge with the minimum safety factor, of all wedges computed by the Combination Analysis. The Minimum Factor of Safety Wedge is displayed by default after the analysis, and the safety factor and summary of results is displayed in the Sidebar.
Minimum safety factor wedge and results summary in sidebar
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Combination Analysis: Histograms and Scatter Plots
The results for ALL wedges computed by the Combination Analysis, are also available, and can be plotted on Histograms and Scatter plots. In general, the analysis output from an Swedge Combination Analysis is similar to the analysis output from an Swedge Probabilistic Analysis. For example:
Failed wedge data can be highlighted in red on the plots
If you double-click on a Histogram or Scatter plot, the nearest wedge
corresponding to that data location will be displayed on the screen, and
the wedge data will be displayed in the sidebar.
Safety factor histogram after a Combination Analysis
NOTE: because the Combination Analysis option is NOT, strictly speaking, a Probabilistic Analysis, a Probability of Failure is NOT reported. If desired, a Probability of Failure can be calculated by dividing the number of failed wedges by the total number of joint combinations. The interpretation of results in this regard is the responsibility of the user.
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Combination Analysis: Stereonet
The Stereonet View for a Combination Analysis can display:
All of the joint orientations (poles) used in the analysis
The intersection orientations of all calculated wedges
Failed wedge orientations
This is illustrated in the following figure.
Stereonet view of combination analysis results showing joint intersections
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Combination Analysis: Import from Dips
Swedge now provides improved integration with the Dips stereonet program. Joint orientations for a Combination Analysis can be imported from a Dips .DIP or .DWP file. This allows you to easily import all joint orientations from a Dips file into Swedge.
NOTE: Dips is a program for the graphical and statistical analysis of orientation data using stereonets, available from Rocscience - click here for more information.
Import from Dips option in Input Data dialog
Dips Import dialog
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