Flexible foundations

Stresses in the subsoil due to the loading of a structure spread with increasing depth. Analytical solutions are available for different loads for the elastic, isotropic half-space.

In further considerations, a distinction must be made between loads from rigid and flexible foundations.

A flexible foundation forms a joint settlement depression together with the loaded soil. The pressure on the underlying soil is known and corresponds to the load above (e.g. backfilled earth embankment, freshly poured concrete).  

In practical applications, the distribution of the bottom normal stress under centric loading is assumed to be constant with P / A, where A represents the loading area. The following sketch shows the theoretical solution and the practical approach for investigations:

In contrast, the vertical displacement of rigid foundations into the ground is the same at every point of the foundation. A settlement depression can no longer form. The vertical stresses must therefore increase toward the edges. Theoretically, stress peaks occur there, but these are corrected to the level of limit stresses permissible for the soil (bearing capacity). For further information please refer to the glossary entry "Rigid foundations".

For more information on calculations of stresses and settlements for flexible foundations, see the glossary entries "Calculation of settlements in geotechnics” and "Calculation of settlements, determination of stresses with the Steinbrenner table​​​​​​​”.