Peak Vs Residual Shear Strength for Landfill Bottom Liner Stability Analyses

The decision whether to use peak or residual shear strengths for a stability analysis must be made in the context of a specific design situation. Yet even when the specific situation is defined, the decision of whether to use peak or residual shear strength is often unclear. In general, if there are potential construction, operation, or design conditions that might cause relative displacement between layers, then a post-peak or residual shear strength for the layer having the lowest peak strength is appropriate. If seismic analyses predict deformation on a given interface, then the design should use the post-peak or residual shear strength for that interface. For bottom liner systems, where stress distribution along the liner system is very complex, it is advisable to verify that the slope stability has a factor of safety greater than unity for residual shear strength conditions along the critical interface.