1. GLE/CEE 330: Soil Mechanics Infinite Slope Analysis
Geological Engineering
University of Wisconsin-Madison

2. Learning Objectives
Discuss when infinite slope analysis may be appropriate
Learn basic analysis approach
Describe example problems for total stress analysis (undrained) and effective stress analysis (drained)

3. Common Features of Slope Analysis Methods
Safety factor analysis:
available shear strength of soil
equilibrium shear stress
Shape and location of failure surface is not known a priori but assumed (trial and error to find minimum FS)
Limit equilibrium analysis (static equilibrium)
Two-dimensional analysis

4. Infinite Slope Analysis
Translational failure along single failure plane with failure surface parallel to slope surface.
Ground water table parallel to slope surface
Ratio of depth to failure surface to length of failure zone is small (<10%)
Applies to surface raveling in granular materials or slab slides in cohesive materials (Translational Slides)
Assumed Failure
Surface

7. = angle of failure (and slope) surface
D = depth of failure surface
zw = height of GWT above failure surface
W/b = Weight of element (per unit width)
N/b = Normal force on failure surface
T/b = Shear force on failure surface
SL/b and EL/b = Shear and normal forces on left
SR/b and ER/b = Shear and normal forces on right (same as left)
Can also account for seepage force

8. Effective Stress Analysis (ESA)
For dry granular soil (zw = 0, c’ = 0):
For saturated granular soil (zw = D, c’ = 0):
Total Stress Analysis (TSA)
FS decreases with depth

9. Example 1

10. Example 2 Water has two effects:
1) increases driving forces because unit weight increases
2) decreases resisting forces because effective stress decreases