Landslides - Infinite Slope Factor-of-Safety Model

Ronda Strauch, University of Washington-Seattle Campus
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This activity is designed to expose students to one of the classic equations used by geologist and engineers to investigate and understand the stability of a hillslope, especially as it relates to soil moisture. Students will learn the infinite slope stability model for estimating the "Factor of Safety" for slope stability. They will also experiment with changing the parameters of the model to explore a sensitivity analysis. There are 3 exercises for students to go through that advances their understanding of landslides.

Intended Audience

This unit is intended for upper level undergraduate and graduate students in hydrology, environmental engineering/sciences, and geology/earth sciences.

Conceptual Learning Outcomes

1. Students learn what factors contribute to hillslope stability and instability.
2. Students will discover how sensitive stability is to different factors.
3. Students will learn how spatially variable site characteristics influence stability.
4. Students will explore the stability consequences of factors affected by changes in climate.
5. Students will practice critical thinking, be exposed to 'big data' and how to analyze them, and diagnose the reasons for and applications of analytical results and model outputs.

Practical Learning Outcomes

1. MS Excel and spreadsheet-based calculation and visualization of a simple model
2. Accessing data online to better grasp place-based data and available tools
3. Prediction and estimation of the effects of varying a key model parameter on model results
4. Use of parameter distributions and Monte Carlo simulations to capture uncertainty and identify a spatially-distributed probabilistic landslide hazard

Student Time Required

3 - 5 hours

Supporting Reference Documents and Files

Reference Videos and Documents:
1. When Nature Strikes - Landslides
About a 5-minute video on landslides in Washington, specifically at Oso and near Mount Rainier.
2. USGS (2004) Landslide types and processes: Fact Sheet 2004-3027.
3. The Water Cycle and Climate Change
Provides global maps of changes in precipitation intensity, stream runoff, and drought
4. Basic information on factor of safety:

Attached Files for exercises:
1. Landslide_Module_Unit - Complete instructions for unit exercises. Instructions for Landslides - Infinite Slope Factor-of-Safety Model Unit (Microsoft Word 2007 (.docx) 40kB Sep28 16)
2. FS_exercise - Excel exercise using the factor-of-safety equation Excel exercise for students to use in exercises 1 and 2 (Excel 107kB Jul20 16)
3. Landslide_Part2_Student_Handout - Hand out for students that accompanies the FS_exercise (exercise 1) and the graphing exercise (#2) Student Handout for Excel and graphing exercises (Microsoft Word 2007 (.docx) 120kB Aug1 16)


This activity has been designed as three exercises that are walked through step-by-step in the "Landslides_Module_Unit" file. Each of the exercises has a series of questions for the students to answer that will help them understand the relevance of the exercise. The first exercise has the student use Excel to understand and explore the factor of safety equation, including impacts from modifying the factors within the equation. The second exercise works on the students graphing ability and provides a visual way of seeing how factor of safety changes given relative wetness and slope. The final exercise exposes the students to real world data and the earth surface modeling using Landlab. Data and use of Landlab is provided on the web through HydroShare – an internet resource designed for sharing, acquiring, and collaborating with hydrological data. After going through the reference video and documents above, step through these exercises for a broad introduction to hillslope stability and what drives the changes we see and experience in the landscape around us.
Students not familiar with Excel may struggle a bit. They will need to be careful in reading and following instructions during the final exercise using Landlab in Hydroshare on the web because it will exposed them to computer programming. However, some of the programs execution can take a few seconds or even minutes, so students need to be patient. If the server hosting the data crashes, students should be patient and try restarting. By in the end, they will be surprised as to what they accomplish.

Steps within this lesson

Specific steps of this lesson are provided within the instructions page in Landslide_Module_Unit and in the Landslide_Part2_Student_Handout files.


There are a series of questions with each exercise designed to help them understand the concepts and applicability. Expect them to answer these questions as best they can; groups of 2-3 might be helpful so they can discuss the questions.
The graphing exercise will produce a graph that can be turned in.
Exercise 3 with Landlab's 'landslide' component will produce outputs such as text, data, and figures that can be screen captured and turned in.