GEOL 118 Lecture Notes - Lecture 20: Slope Stability, Shear Strength, Quick Clay
4 Apr 2016
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Geol 118 - lecture 20 - landslides ii. Driving forces- downslope weight of slope/earth materials ( gravitational pull) Resisting forces- shear strength ( amount of sideward directed force needed to cause failure) that holds slope in place. Steeper slopes create a larger force imbalance. Evaluate slope stability by calculating safety factor (sf): Sf = resisting force (fr)/ driving force (fd) = fr/fd. If sf> 1 then fr>fd, slope is stable. Driving forces exceed resisting forces and slope is unstable. Driving force (weight directed downslope) calculated using trigonometry. Consider balance of forces for translational vs. rotational slides. Translational slide (planar failure surface) - common for rock substrates. Rotational slide (curved failure surface)- common for soil self-stabilizing; resisting mass quickly increases, stops landslide. Shear strength depends on two physical properties. Cohesion- ability of particles to stick together due to electrostatic forces. Shear strength also depends on friction (resistance to motion between grains, related to grain size and shape)
