GALENA - enables you to define the failure surface in terms of the actual slope

GALENA Categories: civil engineering, geotechnical, slope analysis

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Restraints and Searching

In the real world, engineers are only concerned with stability within certain physical limits. GALENA introduced the concept of Restraints to allow you to focus your investigations on realistic failure surfaces that take account of geological structure.

GALENA's Restraints are based on those parameters and values that are used to define a failure surface so that you have total control over the extent of the search area.

As an example: You are considering a slope where you have concluded a circular failure surface to be most appropriate. Restraints allows you to limit all trial failure surfaces to daylight at the toe of the slope which we will take to be the X-Left position for the failure surface. Restraints also allows you to define a range for the other end of the failure surface which will be the failure surface X-Right position and a range for the failure surface Radius.

All failure surfaces then generated by GALENA will be within the ranges defined for the X-Right position and the Radius, and all failure surfaces generated will have the same X-Left position.

Restraints can of course be used to provide search limits to any of the parameters used to describe circular failure surfaces including the more traditional abstract points in space used to define a circle center. Restraints can also be used in a similar way to provide search limits for non-circular failure surfaces and truly provide you with control over search areas.

As well as providing search ranges, Restraints allows you to define the number of trial surfaces to be generated and analyzed within each of those ranges. The actual number of trial surfaces is up to you. GALENA can generate and analyze up to around 1 billion trial surfaces for each analysis although it would be rare to attempt such numbers.

The norm would be to follow a sequential 'fine-tuning' approach with around 3,000 - 5,000 trial surfaces for an analysis followed by further analyses using the critical failure surface as a seed.

So, as you can see, Restraints provides you with a very powerful mechanism that gives you real control in the real world.

The image below shows a model with an evenly distributed load adjacent to the slope toe and an unevenly distributed load behind the slope crest - critical to the stability of the slope is the thin, weak clayey layer within the slope and the perched water table (piezometric surface) therein.

Restraints in GALENA allow the user to define the horizontal search range for both the left and right positions of the failure surface and for the vertical search range within the weak layer.

Restraints also allow the user to fix the left position of the failure surface (as is most likely in this case due to the adjacent loading) and to concentrate the search for a failure surface with the lowest Factor of Safety in the area around the upper unevenly distributed load.