Undulated Slip Surface
If the undulated surface is considered (on scale 1 to 10 m) - it is possible to account for slip surface waviness by angle ν:
slip surface gradient
gradient of the i-th fault of the slip surface
The waviness increases the tensile strength τ on the slip surface by Δτ:
normal stress acting in the direction normal to the slip surface
Undulated slip surface
Miller, S.M. (1988). Modeling Shear Strength at Low Normal Stresses for Enhanced Rock Slope Engineering, Proc. Of 39th Highway Geology Symp, 346-356.