Typology of ground movement risks Ground movement risk is divided into four types of phenomena, each very different from the others. Subsidence and collapse due to the presence of subterranean cavities (both natural and artificial: tunnels built during war, mushroom beds, salt or stone extractions, etc.). Subsidence is a basin-shaped topographical depression caused by a gradual sinking of surface land; a collapse is a sudden failure of pillars or the upper part of a cavity, which literally creates a “hole” (cave-in) on the ground’s surface. Rockslides or rock falls, caused by the natural erosion of cliffs and rocky slopes cause large volumes of rocks to tumble over great distances at high speeds. Landslides are displacements of a mass of land (which can be tens of meters deep) along the ground’s surface, generally at a slow pace. If the surface (known as the fracture surface) gives way, the landslide can move very quickly, especially if it is saturated with water. Swelling and shrinking of clay-based soil is caused by variation in its water content and can affect buildings and structures to varying degrees (due to cracking). During dry periods, the absence of water leads to irregular settling of the surface soil. An influx of water, on the other hand, causes ground swelling.
Typology of ground movement risks Ground movement risk is divided into four types of phenomena, each very different from the others. Subsidence and collapse due to the presence of subterranean cavities (both natural and artificial: tunnels built during war, mushroom beds, salt or stone extractions, etc.). Subsidence is a basin-shaped topographical depression caused by a gradual sinking of surface land; a collapse is a sudden failure of pillars or the upper part of a cavity, which literally creates a “hole” (cave-in) on the ground’s surface. Rockslides or rock falls, caused by the natural erosion of cliffs and rocky slopes cause large volumes of rocks to tumble over great distances at high speeds. Landslides are displacements of a mass of land (which can be tens of meters deep) along the ground’s surface, generally at a slow pace. If the surface (known as the fracture surface) gives way, the landslide can move very quickly, especially if it is saturated with water. Swelling and shrinking of clay-based soil is caused by variation in its water content and can affect buildings and structures to varying degrees (due to cracking). During dry periods, the absence of water leads to irregular settling of the surface soil. An influx of water, on the other hand, causes ground swelling.
