## Landslides

### Definition :

Landslides affect soils and typically involve large masses of terrain detaching and sliding down a slope or embankment. They can be triggered by:

- Natural events (heavy rain, bank erosion, mechanical degradation, earthquakes)

- Human actions (earthworks, deforestation, dam/levee construction)

The speed of failure can vary greatly. Sometimes, the collapse is preceded by warning signs (e.g., cracks forming, bulging ground), but it can also occur suddenly (within seconds to minutes). The slip surface is often planar or circular.

Slide caused by earthworks (Jijel Bypass, 2008)

### a. Planar Slides

The failure surface is mostly planar, following a thin layer with poor mechanical properties, often prone to water seepage (e.g., a permeable loose surface layer overlying an inclined bedrock stratum).

Schematic Representation of Different Types of Landslides

### b. Rotational Slides (Single)

This is the most common type of landslide. The failure surface has a simple shape and can be approximated as a cylindrical section.

### Example :

The first photo shows a landslide that occurred in 2009 on the national road RN 29 in Boumerdes Province. Additionally, the second photo illustrates an embankment slope failure that occurred in 2006 during fill repair works on a section of the RN[1] 79A roadway in Mila Province.

Rotational slide on RN 29 (Boumerdes, 2009)
Embankment slide during RN 79A repair works (Mila, 2006)

### Definition : c. Complex Rotational Landslide

This type involves multiple nested rotational slide. The initial failure at the slope toe removes lateral support for upslope material, triggering a retrogressive succession of rotational failures that progress uphill through a "domino effect."

## Notes

1. RN: National Road (Route Nationale)