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# Piezo Line Statistics

If your model includes one or more Piezometric Lines (to calculate pore pressure), then the Pressure Head represented by the location of a Piezo Line, can be treated as a Random Variable in a Slide2 Probabilistic Analysis.

To define Piezo Line pressure head as a random variable:

1. Select Statistics > Piezometric Lines. You will see the Piezometric Line Statistics dialog.
2. TIP: you can also right-click ON a piezo line, and select Statistical Properties from the popup menu. This is a convenient shortcut to the Piezo Line Statistics dialog.

3. Select the Piezometric Line Number (the ID number) of the Piezo Line for which you would like to define Pressure Head statistics.
4. Select the Pressure Head checkbox.
5. Now define the statistical parameters for the Piezo Line Pressure Head. Select a Statistical Distribution, and enter a Standard Deviation (if applicable), and Relative Minimum and Maximum Values.
6. The Mean Value of the Piezo Line Pressure Head random variable is equal to ZERO. The Random Variable that you are defining is the Pressure Head DIFFERENTIAL, relative to the location of the piezo line. See below for more information.
7. For more information about the statistical parameters which are used to define Random Variables in Slide2, please see the Random Variables topic.

## Piezo Pressure Head Random Variable

The Random Variable that you are defining for a Piezo Line is the Pressure Head DIFFERENTIAL, relative to the graphical location of the Piezo Line boundary on the model. It is NOT the absolute value of the Pressure Head. During the Probabilistic Analysis, the value of the Pressure Head random variable is added to the y-coordinate of each vertex of the Piezo Line. In this way, the entire Piezo Line is moved up (or down), according to the randomly sampled value of the Pressure Head differential.

## Sensitivity Analysis

If you are performing a Sensitivity Analysis using the Piezo Line Pressure Head, then you must define Minimum and Maximum values in the Piezometric Line Statistics dialog, as described above for a Probabilistic Analysis. The Sensitivity Analysis will be carried out by uniformly varying the Pressure Head differential, between the Minimum and Maximum values, in 50 equal increments.

• If you are performing a Sensitivity Analysis, but you are NOT performing a Probabilistic Analysis, then the Distribution and Standard Deviation options will be disabled in the Piezometric Line Statistics dialog, since they are not applicable for a Sensitivity Analysis.
• If you are performing BOTH a Sensitivity Analysis AND a Probabilistic Analysis, then the Sensitivity Analysis will use the Minimum and Maximum values you have defined for the Pressure Head. It will ignore the parameters which are not relevant to the Sensitivity Analysis (i.e. Distribution and Standard Deviation, which are only applicable for the Probabilistic Analysis).