Back Analysis of Support Force

A Back Analysis in Slide allows you to calculate the total support force required to achieve a specified factor of safety. For details about the Back Analysis option, see the Back Analysis of Support Force topic in the Slide Model section of this Help system.

If a Back Analysis has been carried out, then the slip surface determined by the Back Analysis and the required support force, can be displayed on the model in the Slide Interpret program.

Show Back Analysis Surface

By default, the surface determined by a Back Analysis, will automatically be displayed when you open the file in Interpret.

The display of this surface, can be turned ON or OFF, by selecting the Show Back Analysis Surface option in the toolbar or the Back Analysis sub-menu of the Data menu.

NOTE: this is the slip surface which requires the MAXIMUM amount of stabilizing force in order to achieve the specified factor of safety, OF ALL SLIP SURFACES ANALYZED.

Active Force / Passive Force

The required support force, can be assumed to act in either a PASSIVE or ACTIVE manner, in the limit equilibrium calculations. For a discussion of the significance of ACTIVE and PASSIVE support force, see the Active / Passive Force Application topic, in the Slide Model section of this Help system.

When the Back Analysis is carried out by the Slide COMPUTE engine, the required support force is always calculated using BOTH assumptions. The Back Analysis is actually performed independently for each assumption (ACTIVE and PASSIVE).

When the slip surface determined by the Back Analysis is displayed on the model, the required support force is also displayed. A horizontal force arrow, at the specified elevation, will be displayed, as shown in the figure below.

image\back_analysis1.gif

Back Analysis slip surface and force displayed on model

By default, the PASSIVE force is initially displayed, when a file is opened in Interpret. Either the ACTIVE or PASSIVE force can be displayed on the model, by selecting the desired option (Active or Passive) from the toolbar (use the drop-down shortcut menu beside the Show Back Analysis Surface toolbar button), or from the Back Analysis sub-menu of the Data menu. NOTE:

Support Design Using the Back Analysis Results

So how can the Back Analysis results be used to design a support system? The results might be used as follows:

Summary of Results in Info Viewer

A summary of all Back Analysis results can be found in the Slide Interpret Info Viewer. The Active and Passive force required, for each limit equilibrium analysis method performed, will be listed in the Info Viewer.