The foundation is part of the building, which transfers to the ground all permanent and variable loads acting on the structure. Building, foundation and subsoil work together. This cooperation depends on the type of building structure, foundation and type of substrate. Topsoil, closer to the ground surface, they are usually weaker. Bearing capacity, soil depends on the type of soil. In case of insufficient bearing capacity of the substrate, significant subsidence of the foundations usually occurs. If there are soils of different classes in the substrate of the same building, then the unequal settlement of foundations arises, which can cause damage to buildings.

In the PN-86 / B standard-02480 the division of land is given taking into account such features, how: origin, cracks, graining, compaction, humidity, plasticity and organic content.

According to the origin, the following division of land is assumed:
a) native land: rocky, non-rocky mineral and non-rocky organic,
b) embankment land.

Rocky land

Rocky soils - due to their strength - are divided into hard ones with strength above 5 MPa and soft with a strength below 5 MPa. In addition, due to the degree of fracture, rocks are distinguished:
- solid, with no visible cracks,
- little cracked with gaps occurring not more densely than what 1,0 m and the width of the gaps less than 1,0 mm,
- moderately cracked with gaps more densely than what 1,0 m and the width of the gaps not greater than 1,0 mm, or with gaps not more densely than what 1,0 m and a width greater than 1,0 mm,

- very cracked with gaps wider than 1,0 mm and occurring more densely than co 1,0 m.

Solid rocks are a good foundation for foundations. However, it is necessary to check the foundation of the foundations, so that these rocks do not have too much fracture and weathering, which occurs closer to the ground surface. Buildings founded partly on solid rock and partly on weathered usually show damage. Therefore, it is necessary to strive to place all foundations on a solid rock, or only on rock weathered, it is recommended to check it during the excavation works, or at least deep 1,0 m from the bottom of the foundation there are no rocks or rock blocks.

tmpddcb-1The foundation of buildings on heterogeneous ground: a) on rock and weathered, b) on clay and sand; 1 - dilatation.

In case of finding solid rock at depth 1,0 m foundations should be constructed this way, that buildings are not damaged by uneven settlement. This can be achieved by dividing the building with dilatations running through its entire height.
If the ground layers are so arranged, that they will cause uneven settlement, dilatations should also be used when building the building on non-rocky ground.