Landslide – is a downward drift of loose rock under the influence of gravity, especially when lose material is saturated with water. It is one of the forms of a disaster.
Emergence of landslides
Landslides are triggered on a section of a slope or incline due to the disruption of rocks balance, caused by increased steepness of the slope as a result of underwashing, weakening of rock strength during weathering or overmoisturization by precipitation and ground waters, impact of seismic tremors, as well as construction and industrial activities that do not take into account the geological features of an area (destruction of slopes by roadway excavation, excessive watering of gardens and patches located on slopes and other).
Development of landslides
Landslides are triggered by an incline of soil layers in the direction of a slope, cracks in rocks that are also directed towards the slope incline. In very moist clayey rocks landslides take the form of a flow. Landslides cause great damage to farmlands, industrial enterprises, settlements, etc. Bank-protecting structures and drainage facilities are used to fight them, slopes are reinforced by piles and vegetation.
In mountainous areas and in northern regions of the country, the thickness of the soil mantle is only several centimeters and can be easily damaged, but difficult to restore. Landslides are a usual occurrence in those areas, where slope erosion processes actively manifest themselves. They occur when rock masses that make up the mountain slopes lose foundation due to the disruption of rock balance. Large landslides appear more often as a result of a combination of such factors: for instance, on mountain slopes that are formed by alternating water-resistant (clayish) and water-bearing formations (sand-and-gravel and fissured limestone) especially if these layers are inclined to one side or transversed by cracks going in the direction of the slope. Man-created refuse dumps near mines and open pits pose similar danger of landslides being triggered. Destructive landslides that move in the form of an orderless heap of rubble are called stone falls; if the block is moving on a previously existing surface as one whole, the landslide is considered a landfall; landslide in loess, pores of which are filled with air takes the form of a flow (liquefaction slide).
Causes of landslides:
- changes in the stress condition of clay rocks;
- ground waters;
- surface waters;
- some types of human activity;
- seepage of pipe and sewage water;
Landslide warning signs:
- Doors and windows in the house start to stick or jam when being opened and closed;
- cracks appear in the walls and foundation of the house;
- cracks appear and widen on the surface of the ground, on pavements, and roads;
- bulging ground appears at the base of a slope;
- appearance of new outfalls of ground and surface water is observed, fences and trees start shifting away from their initial position;
- a clear noise and increasing underground rumble is heard.
Protection measures for landslides
If the possibility of landslides emerging is great, special measures on protection from landslides are carried out. These include reinforcing landslide slopes, sea and lake shores, river banks with retaining and sea walls and seafronts. Sliding soil is reinforced by piles set up in a chessboard order, artificial freezing of soils is conducted, and vegetation is planted on the slopes. A preliminary drainage with the electro-osmosis method or by pumping hot air into boreholes is conducted for the stabilization of landslides in wet clays. Large landslides can be prevented by draining structures that block the way of surface and ground waters to the landslide material. Surface waters are drained through ditches, ground – with tunnel shafts and horizontal wells. Although such measures are quite costly, implementing them will be cheaper than eliminating the consequences of a disaster that has already occurred.