The construction boom in Germany is continuously growing. Comfortable prefabricated houses and solid buildings are in progress all around. The bearing capacity of the soil is an imperative condition to be evaluated beforehand - particularly below the foundation plate, as this element represents the interface between house and subsoil. It is the purpose of the foundation plate to distribute the weight of the building in a homogeneous manner and to protect the building from heat/cold and vibrations of the ground. The available ground however is often not strong enough to carry the foundation plate without additional earthwork. Therefore besides deep sounding, analysis of the bearing capacity of the grown soil is required. A light weight deflectometer is an adequate instrument, since it is able to perform a measurement within only two minutes. The simple service as well contributes to a quick establishment of comprehensive measurement sequences. This way, a qualified assessment concerning the entire field is possible in no time. In the case of cohesive soil or inclination of the site, soil replacement has to be carried out. Sometimes several meters can be involved. For these works, it is important that the new soil is inserted by layers and that these layers are individually compacted by vibratory plate. Thickness of each layer should not exceed 30 cm, and evidence of qualified compaction must be provided each time. For this inspection, a light weight deflectometer is an ideal instrument. Minimum requirement for the bearing capacity of soil for private homes usually amounts to 30-40 MN/m² for the layer directly below the foundation plate.
„During each construction project, we carefully examine the quality of the earthwork for cellars and foundation plates. Compaction work and subsequent compaction control is of major importance. Particularly in places with difficult access, there is no alternative to light weight deflectometers. They do not need a counterweight, and the assessment is easy to perform “, declares project manager Kai Wolts. Mr. Wolts and his company recently invested in 14 light weight deflectometers produced by TERRATEST from Berlin. From now on, each construction gang disposes of its own measuring equipment and can immediately provide itself evidence for the compaction of the soil. „This fact ensures our independence from external geotechnical experts, thus saving time and money.”
All around Germany, light weight deflectometers make themselves indispensable, as settlement damages turned out to be a serious topic for several companies, causing major follow-up costs. Particularly for foundation plates, insufficient compaction of the subsoil gives rise to exorbitant expenses, as the whole building may be subjected to cracks. Therefore before pouring the foundation plates, measurement of the bearing capacity of the subsoil is imperative. „Since many years, we trust in light weight deflectometers, and are continuously in action in the vicinity of Berlin with three of them”, emphasizes construction engineer Norbert Wenzel from Frankfurt (Oder). „Besides prescribed core sounding, we are carrying out also measurements by means of light weight deflectometers, to ensure homogeneous bearing capacity and sufficient compaction quality of the soil, before pouring the foundation plate. This is an essential element of responsible construction management”, so his opinion.
The essential benefits of light weight deflectometers are obvious:
- Measurements can be carried out by each capable member of the team in no time.
- Large measurement sequences are possible even under tight deadlines, as each measurement takes only two minutes.
- Counterweights like road rollers are not necessary.
- Compaction work for each layer can be accompanied by measurements.
- Homogeneity of bearing capacity can be checked already during insertion of the layers.
