5.1.1. More details on sinking consequences

Sinking is a very slow process of vertical deformation with a limited extent (like limited progressive subsidence). The differential deformations can be caused by:

  • The natural consolidation of recent soil formations (Quaternary), under load (weight of overlying grounds and additional weight of constructions). Typical examples for constructional problems/damage due to sinking are the Towers of Pisa and Bologna (Italy), and the Church Saint-Jean in Caen (France);
  • The lowering of groundwater table by pumping. Typical examples are the cities Mexico, Venice, and Bangkok;
  • The exploitation of fluids (like oil in California) or gas (in the Plain of the Po) in soil and rocks.
  • The alternation of humidification and desiccation cycles in clayey soils (e.g. shrinking and swelling);
  • The modification of the stresses in granular soils (liquefiable sands).
Fig.1.Differential sinking beneath the foundation of the Tower of Bologna (Italy) (Photo: Maquaire, Cerg)
Fig.2.Differential sinking affecting the Tower of Pisa (Photo: Castaldini, Cerg).
Fig.3.Topple and deformation of the Saint-Jean Church (Caen, France) due to a major sinking underneath its foundations. The church has been built in the XVth century in a marshy zone of the alluvial plain of the Orne River and is constructed on oak piles. As sinking has appeared during the construction phase, the high of the tower has been limited to reduce its total weight and to decrease the toppling force. (Photo: Maquaire, Cerg).