Slope Stability & Soil Stabilization

• Lime treats plastic clays: it lowers the plasticity index and dries the soil. Portland cement suits granular and low-plasticity soils.
• Geosynthetics serve four functions: reinforcement, separation, filtration and drainage. A geotextile under a base course is usually there for separation.

Worked: a sand embankment face

A 2.5H:1V slope in sand with φ = 34°: tan β = 1/2.5 = 0.40, so dry FS = 0.675/0.40 = 1.69. After heavy rain saturates it with flow parallel to the face, γ_sat = 125 pcf and γ′ = 62.6 pcf: FS = (62.6/125) × 1.69 = 0.84. The slope that stood all summer fails.