Shallow foundations

Foundations transmit the building's forces to the ground via all its geometric elements (base and sides). Depending on the type of foundation, the influence of these elements is more or less preponderant.

One of the characteristics of foundations that enables them to be classified into families is their embedment, defined as the depth between the base of the foundation and the ground surface.

Shallow foundations are characterized by a low level of embedment in relation to their dimensions, which means that the transmission of forces to the ground favors the base rather than the lateral elements.

There are several types of checks to be carried out when dimensioning shallow foundations, based on an analysis of the various interactions between the soil and the structure.

Checking the bearing capacity of the soil is the most intuitive. It ensures that the soil is capable of supporting the loads of the structure. However, the force torsor induced by the structure or external elements is not necessarily vertical. In some cases, therefore, it may be essential to check for slippage between the base of the foundation and the ground.

These forces induce deformations in the soil, which also need to be understood. Here too, the most intuitive (and most common) deformations are settlements, i.e. vertical deformations of the underlying soil.

It's also important to ensure that the materials used in the foundations are strong enough to withstand the forces they will support.

Finally, it is important to check that the foundations are stable in their general environment, which is particularly important when the building is located in sensitive areas such as slopes, embankments, etc.

Although all these checks must be carried out for each foundation, their importance must be understood and prioritized by the geotechnical engineer, who will then decide what needs to be included in the design.

The aim of this article is to provide the keys to carrying out these checks, by reviewing the approaches used and the ways in which they can be integrated into the standardization framework provided by Eurocodes 7 and 8 and their application standards.