Quantitative Skills > Teaching Resources > Activities > An Assessment of Hill Slope Stability Using the Factor of Safety

An Assessment of Hillslope Stability Using the Factor of Safety

Laura Moore, Oberlin College
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This activity was selected for the On the Cutting Edge Exemplary Teaching Collection

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This activity has benefited from input from a review and suggestion process as a part of an activity development workshop.

This activity has benefited from input from faculty educators beyond the author through a review and suggestion process as a part of an activity development workshop. Workshop participants were provided with a set of criteria against which they evaluated each others' activities. To learn more about this review process, see http://serc.carleton.edu/quantskills/review_processes.html#2005.

This page first made public: Oct 23, 2009


Students consider the balance of forces on a hillslope using the Factor of Safety by calculating shear stress and shear strength for an example hillslope and formulating an expression for the factor of safety in an Excel spreadsheet. Students then use this spreadsheet to conduct a sensitivity analysis for the purpose of assessing which variables are most important in determining hillslope stability. A series of short answer questions guide students through this process and a series of reflection questions give students the opportunity to consider assumptions and applicability of the factor of safety to the real world. This is a homework assignment that generally takes 1.5 to 2 hours for students to complete.

Learning Goals

Context for Use

This activity works well when assigned as a problem set to be completed individually. It can also be incoporated into part of a lab on mass wasting.

The activity is assigned toward the end of a mass wasting unit in an upper-level Earth Surface Processes class. Prior to receiving the assignment students have developed an understanding of hillslope processes and slope stability through lecture, class activities and a hill slope lab. Immediately preceeding the assignment, the concept of mass wasting as a threshold process is introduced. Equations for shear stress and shear strength are also developed for the infinite slope case and the factor of safety is given as a means for assessing the balance between driving and resisting forces.

The activity is followed by a discussion of the reflection piece of the assignment which leads naturally into presentation of the different types of mass wasting events and how they are classified.

Description and Teaching Materials

Teaching Notes and Tips


Grading involves checking for mathematically correct answers and reasonable verbal explanations. In evaluating the reflection questions, I place greater emphasis on demonstration of a reasonable thought process than on arrival at the correct answer.

References and Resources

Ritter, D.F., Kochel, R.C., and Miller, J.R., 2002, Process Geomorphology (4th ed.): WCB/McGraw-Hill, 560 p.

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