Progressive subsidence is the process of slow surface deformation with or without fractures due to the evolution of natural or artificial caves (subterranean quarry or mines -iron, salt, coal, etc.-), circular or oval cavities or depressions appeared in surface,
What is a progressive subsidence phenomenon?
Subsidence, like sinking, is a very slow process of vertical deformation of large extent. The deformations are triggered by:
- The natural dissolution of soluble materials (karst phenomena),
- The extraction of materials (calcareous, etc.) or extraction of ores (iron, salt, coal, etc.).
Subsidence is a phenomenon relatively slow which can last of many years. It generally occurs in ground terrains with flexible behaviour, or in the case of artificial cavities (subterranean quarry or mines), when the depth of exploitation is important compared to the thickness of the size. Subsidence can be the precursor sign of an evolution by rapid subsidence. Subsidence (with vertical component of the movement) results in low depth of vast topographic depressions, generating relative deformations prejudicial to the structures, or, on a large scale, a disorganization of the system of drainage. In limit of these depressions (called sink hole in case of a karst dissolution), zones in extension (with shearing and traction, yielding stresses) can lead to the appearance of cracks.
Scheme of the progressive subsidence process above a subterranean quarry by slow and progressive deformation of the ground terrain with flexible behaviour. With these indications: below, the extension of the subsidence zone, and. above, the extension of the influenced zone (from BRGM, website BDcavité.net, developed by BRGM).
References:
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