Interslice Force Function

For each of the limit equilibrium Analysis Methods used in Slide, assumptions are made about the angle of the resultant interslice forces, between the vertical slices in a sliding mass. For all methods except the GLE (General Limit Equilibrium) analysis method, the assumed angle is determined by the analysis method, and cannot be changed by the user.

For the GLE analysis method in Slide, the user can specify an Interslice Force Function, which determines the angle of the resultant interslice forces throughout the sliding mass. A number of pre-defined Interslice Force Functions are available, or a user-defined function can be created.

Defining the Interslice Force Function

When the GLE analysis method is first selected in the Project Settings dialog, a Half Sine Interslice Force Function is in effect by default. (The name of the Interslice Force Function which is currently in effect, is indicated in the dialog). It is NOT necessary for the user to specify an Interslice Force Function, unless they wish to use a different function.

To change the Interslice Force Function from the one which is currently in effect:

  1. The GLE checkbox must first be selected.

  2. Select the Change button for the Interslice Force Function.

  3. The Define Interslice Force Function dialog will appear, allowing you to specify the Interslice Force Function. Select the desired function from the Function Name drop-list.

  4. If the function requires user input, then define the function as described below.

  5. When finished defining the function, select OK, to return to the Project Settings dialog. The name of the function you have selected will be indicated in the dialog.

NOTE:

Half Sine

A Half Sine Interslice Force Function has no user-definable parameters. It is only necessary to select the Function Name Half Sine, and select OK, to apply a Half Sine Interslice Force Function.

NOTE: the Half Sine function is always initially in effect by default.

Constant

A Constant function has no user-defined parameters, and is simply a constant function with f(x) = 1 on the range x = 0 to x = 1.

NOTE: using a Constant Interslice Force Function, for the GLE Analysis Method, is equivalent to using Spencer’s Analysis Method.

Trapezoid

The Trapezoid function allows you to specify a trapezoidally shaped function, defined by four points. The default Trapezoid function can be customized by entering appropriate values in the columns at the left of the dialog.

NOTE: the Trapezoid function can be modified graphically, by clicking and dragging on any of the four points defining the Trapezoid in the graph area at the right of the dialog. Note that the left and right points can be moved in a vertical direction only.

Clipped Sine

A Clipped Sine function allows you to define a function which is based on the shape of a Half Sine, but which is allowed to have non-zero f(x) values at x = 0 and x = 1. Only the f(x) values at x = 0 and x = 1 can be specified by the user.

NOTE: the Clipped Sine function can be modified graphically, by clicking and dragging either of the two endpoints, in the graph area at the right of the dialog. The points can be moved in a vertical direction only.

User Defined

A User Defined function allows you to define a fully specified, arbitrary user-defined Interslice Force Function. The only restrictions for a User Defined Function, are:

To create a new user defined function:

  1. Enter the x and y coordinates of the function in the columns at the left of the dialog. As you enter coordinates, you should see the function drawn in the graph area at the right of the dialog.

  2. When all coordinates are entered, select OK.

To edit an existing user defined function:

User Defined Interslice Force Functions can be Exported (saved) in a separate functions file, and Imported into other Slide files, so that you do not have to re-define User Defined Interslice Force Functions each time they are required in a model.

NOTE: Interslice Force Function files in Slide use a .FN1 filename extension.

To Export (save) a User Defined Interslice Force Function:

  1. Select the Export button in the Define Interslice Force Function dialog.

  2. In the Save As dialog, enter a filename, and save the file.

To Import a User Defined Interslice Force Function:

  1. Select the Import button in the Define Interslice Force Function dialog.

  2. In the Open File dialog, open the Interslice Force Function file that you wish to import, and it will be imported into the Define Interslice Force Function dialog. Select OK to save this as the current User Defined Interslice Force Function.