1. Geological Engineering University of Wisconsin-Madison
GLE/CEE 330: Soil Mechanics Introduction to Landslides and Slope Stability
Geological Engineering
University of Wisconsin-Madison

2. Learning Objectives Discuss socioeconomic implications
Discuss basic modes of slope instability
Discuss basic terminology
Discuss case history

3. 2005 La Conchita Landslide 35 deg. slope angle
Poorly-cemented marine sediments
15 days of near-record rainfall
10 confirmed fatalities

4. Factor of Safety =
Shear Resistance
Shear Force

5. Socioeconomic Impacts
Direct Costs – repair, replacement, maintenance
Indirect Costs – loss of productivity, real estate value, tax revenue, injury, death, trauma
Most severely affected nation: Japan (~$4B annually)
USA: ~$1.8B – $2.0B annually
Casualties: ~600 annually worldwide, ~25-50 USA

7. Slope Terminology Top (Scarp) Surcharge Face Terrace Height, H SR 1
SR = Slope Ratio (Horizontal to Vertical)
(e.g., 2:1 or 1:1)
Toe

8. Types of Slope Failures
1) Translational slide (weak layer)
2) Rotational slide (base failure)
3) Rotational slide (“toe slide”)
4) Rotational slide (“slope slide”)
5) Flow slide (viscous fluid behavior)
6) Block slide

9. Failure Modes

10. Toppling Instability
(Varnes)

11. Flow Failure
(Varnes)

12. Rotational Slide
(Varnes, 1978)

13. Block Slide
(Varnes)

14. Triggering Mechanisms
1) Intense rainfall (role of pore pressure)
2) Erosion (removal of toe support, increased slope angle)
3) Earthquake loading (dynamic forces, liquefaction)
4) Construction activities (toe excavation)
5) Surcharge loading
6) Rapid drawdown

15. Case Study: Seattle, WA (USGS)