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Optimization of Circular Slip Surface

The goal of the optimization process is to locate a slip surface with the smallest factor of slope stability SF. The circular slip surface is specified in terms of 3 points: two points on the ground surface and one inside the soil body. Each point on the surface has one degree of freedom while the internal point has two degrees of freedom. The slip surface is defined in terms of four independent parameters. Searching for such a set of parameters that yields the most critical results requires sensitivity analysis resulting in a matrix of changes of parameters that allows fast and reliable optimization procedure. The slip surface that gives the smallest factor of slope stability is taken as the critical one. Parameters of individual slip surfaces and results from optimization runs can be displayed in the output document.

This approach usually succeeds in finding the critical slip surface without encountering the problem of falling into a local minimum during iteration. It, therefore, appears as a suitable starting point when optimizing general slip surfaces such as the polygonal slip surface.  

The optimization process can be restricted by various constraints. This becomes advantageous especially if we wish the searched slip surface to pass through a certain region or to bypass this region. The restriction on the optimization process can be performed in two different ways:

  1. Optimization restrictions are specified as a set of segments in a soil body. The optimized slip surface is then forced to bypass these segments during optimization.
  2. Another way of restricting the optimization process is to fix the location of lthe eft or right endpoint of the optimized slip surface.
  3. Restricting the optimization process can be also excluding of slip surfaces with a lower weight of soil above the slip surface than the specified minimum.

For ITF methods, the surplus sliding force can be used as the criterion of optimization. In that case, the optimization process searches the slip surface with a maximum value of surplus sliding force Fn instead of the minimum stability factor FS. This optimization criterion can be applied when the actual slip surface is not acceptable. For an acceptable slip surface, the optimization process uses the stability factor FS only.

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