Cohesionless fill slope on saturated clay foundation

The following problem for verification is the hypothetical embankment reviewed in Duncan, J.M., Wright, S.G., and Brandon, T.L., 2014. Soil Strength and Slope Stability, Second Edition. It is a 100 ft high embankment of cohesionless fill with 2H:1V slopes, resting on a saturated clay foundation 50 ft thick.

The embankment fill is purely frictional (φ = 40 o) and is considered to have drained completely during construction. The clay foundation is assigned an undrained shear strength of cu = 2500 psf based on UU testing to represent the short-term end of construction stage.

The geometry and material parameters are shown below.



Analyses were carried out with Auto Search (resolution tolerance of 6) and using the Simplified Bishop's, Janbu's Uncorrected and Corrected, and Spencer's methods. The table below compares the published results to the analyses carried out using MacSlope.

Published Results

MacSlope Results

Case
FOS
Bishop's Simplified
1.22
Janbu's Simplified (Uncorrected)
1.07
Janbu's Simplified (Corrected)
1.16
Spencer
1.19
Case
FOS
Bishop's Simplified
1.212
Janbu's Simplified (Uncorrected)
1.061
Janbu's Simplified (Corrected)
1.156
Spencer
1.187

The analysis results for the Spencer method case are shown below.



Download the MobiSlope file with the analysis results for this verification example here.