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Sensitivity Analysis
The effect of uncertainty or variability in the values of input parameters can be explored using a Sensitivity Analysis. In sensitivity analysis, model parameters selected by the user, are varied across a range of values and the effect on safety factor observed. This helps to identify the parameters that have the most effect on wedge stability.
The results of a sensitivity analysis are displayed on a sensitivity plot, which plots the safety factor against percent change in the input variables, as shown in the figure below.
Sensitivity plot of 3 variables
On a sensitivity plot, the gradient of a curve for a parameter indicates the effect that parameter has on the factor of safety. Steeper (rising or falling) curves indicate greater influence on the factor of safety. A relatively "flat" curve indicates that a variable has little effect on the factor of safety. A completely flat curve indicates that the variable has NO effect on the safety factor (within the specified range of the variable).
Input dialog for Sensitivity Analysis
Almost all input variables in Swedge can be selected for a Sensitivity Analysis. This is particularly useful for analyzing support requirements and loading as described below.
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Sensitivity Analysis: Support
Sensitivity Analysis makes it easy to determine the required support parameters necessary to achieve a given factor of safety. Simply enter a range of values for a support parameter (e.g. bolt capacity, shotcrete thickness, support pressure), and from the sensitivity plot you can determine the parameter value which corresponds to a desired factor of safety.
For example, in the following sensitivity plot, a support pressure of approximately 3.8 tonnes/m2 is necessary to achieve a safety factor = 1.5.
Support pressure versus factor of safety
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Sensitivity Analysis: Loading
Sensitivity Analysis makes it easy to determine critical load values. Simply enter a range of values and from the sensitivity plot you can determine the value which corresponds to a specific factor of safety.
For example, in the following sensitivity plot, a seismic coefficient of approximately 0.2 corresponds to a critical safety factor = 1.
Seismic coefficient versus factor of safety
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