Slope failure types and prevention

Types of slope failure

1. Rotational slip (face, toe and base failures): a curved surface in homogeneous clay.
2. Translational (planar) slip: a shallow plane parallel to the slope, in layered soil or cohesionless soil.
3. Compound slip: partly curved and partly plane, over a hard layer.
4. Wedge failure: sliding on intersecting weak planes.
5. Infinite slope failure: shallow slide on a long uniform slope.
6. Falls, flows and creep: rapid fall of blocks or flow of saturated soil, and slow downhill movement.

Measures to prevent slope failure

Reduce the driving forces

• Flatten the slope or reduce its height, or construct benches.
• Remove the load from the top (unload the crest).

Increase the resisting forces

• Add a berm or counterweight at the toe.
• Construct retaining walls, gabion walls, or piles at the toe.
• Use reinforced earth, geotextiles, soil nails or rock anchors.
• Replace weak soil by better material, or compact the soil.
• Provide vegetation and bio-engineering (grass, shrubs, trees) to bind the soil and reduce erosion.

Control water

• Provide surface drains and catch-water drains above the slope to divert runoff.
• Provide sub-surface drains, horizontal drains or sand blankets to reduce pore pressure.
• Seal cracks and use impermeable surface covering where required.
• Provide filters and weep holes behind retaining structures.

Others

• Soil stabilisation by grouting, lime or cement; control vibrations from blasting; and keep monitoring with instruments.