Analysis of internal stability

An internal stability of a structure is checked assuming two types of a slip surface:

-  plane slip surface:

Plane slip surface

- broken slip surface:

Broken slip surface

In both cases a specific slip surface is examined for a variation of angle υ.

When running an optimization analysis the calculation is carried out for all benches with a variation of the angle of slip surface ν changing from 1 up to 89 degrees with a one degree step.

A verification analysis of internal stability can be performed using either the factor of safety or the theory of limit states depending on the setting in the frame "Settings".

The analysis checks whether a ratio of resisting and shear (driving) forces acting on a slip surface is greater than the inputted factor of safety. The following forces are employed: 

Shear forces:

-	component of gravity force parallel to slip surface
-	in case of broken slip surface – component of active earth pressure acting on vertical part of structure and parallel to slip surface (pressure is determined without reduction of input parameters)
-	horizontal forces due to earthquake

Resisting forces:

-	soil friction and cohesion along slip surface
-	sum of forces transmitted by nails