INFINITE SLOPE ANALYSIS THE SIMPLEST WAY TO MODEL LANDSLIDES!

GRAVITY FRICTION AND COHESION NORMAL FORCE GREATER THE NORMAL FORCE THE GREATER THE RESISTING FORCE What is normal anyhow?

AN EXAMPLE WHERE THE ASSUMPTIONS OF A PLANAR SLOPE ARE WELL MET

Driving Force -- Gravity Driving Force  h/cos 

MOHR-COULOMB FAILURE CRITERIA

Normal stress (kN/m 2 )

Resisting Force -- Soil Strength  Resisting Force h/cos 

Factor of Safety F ≤ 1Slope Instability F ≥ 1Slope Stability

CLEARCUTTING AND LANDSLIDES Slide scars

Soil Strength Parameters (Selby, 1993)

Effective Cohesion -- Vegetation Effects from Selby, 1993

 Factor of Safety Effective Root Cohesion (kPa) Till Sand (c = 1 kpa,  = 37 o ) (c = 150 kpa,  = 33.5 o ) saturated 0.75 m slab 35 o slope 25 o slope

Mechanics of Deforestation- Induced Erosion Removal of trees; suppression of vegetation by grazing Roots root or stumps are pulled Cohesion   in two to five years Greatest effect on steep, sandy slopes Consistent with geologic observations