Undermine a foundation

There are always situations in which it would be necessary to undermine a foundation. Especially in buildings, a foundation may not be undermined without further notice. What should be considered when undermining foundations can be read below.

Various reasons to undermine the foundation

The undermining of a foundation as such is not apparent from the corresponding standards. Instead, however, the following works:

  • the endeavor
  • the excavation
  • the foundation

These projects are regulated in DIN 4123. In addition, the Länderbauordnungen are to be considered.

Even the lateral exposure of the foundation problematic

Now, however, it may happen that none of the mentioned work is to be carried out at all and an undermining of an existing foundation still seems necessary.

In this case, too, it should be noted that this work should never be carried out without the help of certified experts. You do not even have to undermine a foundation so that the static of a building is already adversely affected.

What can already happen during the lateral exposure (without sub-excavation)

Sometimes it is sufficient to expose the area to the side of the foundation. This can be represented particularly well on the foundations of very old existing buildings. Until the middle of the 20th century, it was common for houses to be founded on a natural stone foundation.

If soil is removed from the foundation, the entire or partial foundation can be destabilized to such an extent that the foundation stones simply break out laterally. The whole house can be so vulnerable to collapse. Even with concrete foundations, this danger exists.

It should be noted that concrete foundations in buildings can be designed as a strip foundation. In particular, the stable position of strip foundations and foundations in general can be so affected. Because foundations do not only transfer loads vertically but also horizontally.

Measures already in foundation work following the foundation

However, if other or further foundation work has to be carried out directly next to an existing foundation, it is usually necessary to underpin the existing foundation. For this purpose, special methods can be used, as described in part in "lifting foundations".

Endeavor and undermine only with certified specialist companies

But these special techniques are also not always applicable. The boundary conditions and specifications are also regulated in DIN 4123. The strength and type of undercutting or undercutting must meet the requirements of the stability analysis. This assumes that this work is carried out by a structural engineer or architect. It may also be necessary to obtain a hydrogeological soil survey.

Tips & Tricks

When undertaking the Untergraben is then always at intervals. These distances must be observed both in depth below the foundation and in length. Of course, the corresponding DIN apply here as well.

Artikelbild: JGA / Shutterstock

Video Board: How To Undermine Existing Concrete Foundation Footings - Room Additions