Tutorial_05_Water_Pressure_Grid.pdf

Water Pressure Grid Tutorial

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Water Pressure Grid Tutorial

This tutorial will demonstrate how to use a water pressure grid to model

pore water pressure in Slide . Two different ways of modeling ponded

water will also be discussed.

MODEL FEATURES:

• pore water pressure grid (total head)

• ponded water above slope, defined by water table

• circular surface search (Grid Search)

NOTE:

• the finished product of this tutorial (file: Tutorial 05 Water

Pressure Grid.sli ) can be found in the Examples > Tutorials folder

in your Slide installation folder.

• This model is also presented in the Groundwater Tutorial (file:

Tutorial 07 Groundwater Seepage.sli) . A seepage analysis is

carried out, and results are compared with the Water Pressure Grid

tutorial.

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Model

If you have not already done so, run the Slide Model program by double-

clicking on the Slide icon in your installation folder. Or from the Start

menu, select Programs → Rocscience → Slide 5.0 → Slide.

If the Slide application window is not already maximized, maximize it

now, so that the full screen is available for viewing the model.

Limits

Let’s first set the limits of the drawing region, so that we can see the

model being created as we enter the geometry.

Select: View → Limits

Enter the following minimum and maximum x-y coordinates in the View

Limits dialog. Select OK.

These limits will approximately center the model in the drawing region,

when you enter it as described below.

Project Settings

In order to use a water pressure grid for pore pressure calculations, we

must first set the Groundwater Method to one of the three available pore

pressure grid options (Total Head, Pressure Head or Pore Pressure) in

the Project Settings dialog. In this case we will be using a grid of discrete

Total Head values.

Select: Analysis → Project Settings

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Enter a project title – Water Pressure Grid Tutorial . Select the

Groundwater tab, and set the Groundwater Method = Grid (Total Head).

Select OK.

Note that Slide can use one of several different methods for interpolating

pressures at any point in the soil, from the grid values. We are using the

default method (Modified Chugh). See the Slide Help system for a

description of the interpolation methods available in Slide .

Add External Boundary

The first boundary that must be defined for every Slide model, is the

External Boundary. To add the external boundary, select Add External

Boundary from the toolbar or the Boundaries menu.

Select: Boundaries → Add External Boundary

Enter the following coordinates in the prompt line at the bottom right of

the screen.

Enter vertex [esc=quit]: 15 20

Enter vertex [u=undo,esc=quit]: 65 20

Enter vertex [u=undo,esc=quit]: 65 35

Enter vertex [c=close,u=undo,esc=quit]: 50 35

Enter vertex [c=close,u=undo,esc=quit]: 30 25

Enter vertex [c=close,u=undo,esc=quit]: 15 25

Enter vertex [c=close,u=undo,esc=quit]: c

Note that entering c after the last vertex has been entered, automatically

connects the first and last vertices (closes the boundary), and exits the

Add External Boundary option.

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Adding a Water Pressure Grid

Now let’s add the water pressure grid to the model. To add a water

pressure grid, select the Water Pressure Grid option from the Boundaries

menu.

Select: Boundaries → Water Pressure Grid

The points defining a water pressure grid can be entered in this dialog,

by entering X and Y coordinates, and a value (in this case, Total Head),

defining the pressure at each grid point.

Figure 5-1: Water Pressure Grid dialog.

Rather than entering the data manually, to save time, there is a water

pressure grid file, in the Examples > Tutorials folder, which you can

simply read in, using the Import button in the Water Pressure Grid

dialog.

Select the Import button in the Water Pressure Grid dialog.

You will see an Open file dialog. Water pressure grids can be imported

from various file formats in Slide , including:

• files with a .PWP filename extension. (These are simple ASCII text

files, where each line of the file contains X, Y and VALUE for one grid

point), or

• .DXF format files (useful if a flownet has been digitized using

AutoCAD, for example)

We will read in a .PWP file.

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1. Open the file called Tutorial 05 Water Pressure Grid.pwp . The

grid data appears in the Water Pressure Grid dialog.

2. Now select OK in the Water Pressure Grid dialog, and the grid will

be added to the model. Each blue triangular symbol represents one

grid point.

Your model should appear as follows:

Figure 5-2: Water Pressure Grid added to model.

Water pressure grid data such as this could come from a flow net, field

measurements, or a numerical analysis, such as the groundwater seepage

analysis which is available within the Slide program.

In this case, the values at each grid point are Total Head values, which

were originally obtained by digitizing the flownet in Figure 5-3, using a

digitizing tablet and AutoCAD. (The grid was originally saved as a .DXF

file, and then converted to a .PWP file).

Remember that Slide also has the capability of using pressure head or

pore pressure grids, as selected in the Project Settings dialog.

Slide v.5.0

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