August 2005
	In this issue:  SLOPE/W Slip Surface Optimization   Mentorship in Ethiopia   New Tutorial Movies

SLOPE/W Slip Surface Optimization
Trial slip surfaces in a limit equilibrium stability analysis are usually a pre-defined geometrical shape, such as the arc of a circle, linear line segments, or a combination of circle arcs and line segments. Recent research has explored the possibility of incrementally altering portions of the trial slip surface to determine if there are perhaps other slip surface shapes that give a lower factor of safety. A variation of the published techniques has been implemented in the latest version of SLOPE/W, where after finding the critical slip surface by one of the more traditional geometric methods, a new segmental technique is applied to optimize the solution.

First, the slip surface is divided into a number of straight line segments. Next, the end-points of the line segments are moved to probe the possibility of a lower factor of safety. The line end-points are moved within an elliptical search area using a statistical random walk procedure, based on the Monte Carlo method, until the lowest factor of safety has been found.

The following diagrams show how a circular critical slip surface is modified through the optimization process. In this case the upper material is somewhat stronger than the underlying soil, which tends to alter the slip surface shape. The factor of safety drops from 1.783 for the circle slip surface to 1.705 for the optimized slip surface. This is typical. Often the optimization leads to a non-geometrically definable shape that has a lower factor of safety than the geometrically definable shape.

Mentorship in Ethiopia
John Krahn, President and CEO of GEO-SLOPE, together with Professor S. Lee Barbour from the University of Saskatchewan, will be traveling to Ethiopia this month as part of a six-year capacity building project funded by the Canadian International Development Agency (CIDA) to help the Ethiopian government reduce the impact of drought and move toward food self-sufficiency. Agriculture and Agri-food Canada – PFRA is managing the project for CIDA. The project is located in the Tigray Region of Northern Ethiopia, an area of the country often affected by drought and resulting food shortages.

The purpose of the project, known as WHIST (Water Harvesting and Institutional Strengthening in Tigray), is to increase water harvesting and its use for food production by strengthening the technical and management expertise of the local government agencies. To achieve this, WHIST is providing a mentoring program that uses Canadian engineering and agronomy experts. WHIST is pursuing the project goals through new irrigation infrastructure development, improved irrigated agricultural practices and better soil and water management. Stay tuned for a follow-up report from John when he returns from Ethiopia.

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