James Bay Dike

The following problem for verification is a cross section from the James Bay hydroelectric project, reviewed in Duncan, J.M., Wright, S.G., and Brandon, T.L., 2014. Soil Strength and Slope Stability, Second Edition. The aim of this verification problem is to illustrate the significant differences between circular and composite slip surfaces.

The geometry and material parameters are shown below.

Circular slip surface

The minimum factor of safety reported for a circular slip surface for this problem is 1.45.

In order to find the critical circular slip surface above the very strong till, the strength parameters for the till were set to be c = 250 kPa and Φ = 50^o. An auto search was completed with an auto resolution tolerance of 2 and a maximum slice width of 5m. The analysis results are shown below. The factor of safety is 1.454.

Composite slip surface

The minimum factor of safety reported for a composite slip surface for this problem is 1.17.

In order to find the critical composite slip surface, the till was set to be an impenetrable region. This allows circular slip surfaces to slide along the top of the till. An auto search was completed with an auto resolution tolerance of 2. The resulting minimum factor of safety calculated using the Spencer method was 1.168. The analysis results summary and heat safety map for the analyzed slip surfaces are shown below.

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