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Risse, Setzungen, Schieflage.

Cracks, subsidence, tilting.

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Practical knowledge

The load of a structure generates additional compressive stresses in the ground, which are associated with settlement. Under the foundation, the stress distribution takes the form of an onion, known as a pressure onion. The stresses are greatest directly under the base surface. They gradually decrease with increasing depth.

As a rule of thumb, the effect of the pressure onion is largely eliminated at a depth corresponding to twice the width of the foundation. Consequently, settlement primarily occurs in this zone, and measures to reinforce the building ground should concentrate on this depth range.

Signs of building settlement

The following observations indicate settlement:

Cracks in masonry
Stepped cracks in walls
Diagonal cracks in walls
Stress cracks in the building structure
Cracks are widening
Expansion joints are expanding and cracking
Connection joints open, the higher the higher
Sticking windows and doors
Doors slamming shut on their own
Marbles roll across the floor on their own
Noticeable tilt: a floor with a slope of about 3-5% is noticeable when walking
Corner of the house sinking
House tilting

Potential damage caused by building subsidence

Settlement distributed evenly across the base area is usually not a problem for buildings. However, if settlement is uneven, deformation stresses occur. Minor differences in settlement are absorbed by the building structure without causing damage. However, the potential for damage increases as the difference in settlement increases. The following assessment generally applies:

Value	Potential for damage
Δs/ℓ < 1/500	Settlement is hardly harmful
Δs/ℓ > 1/300	architectural damage is possible
Δs/ℓ > 1/150	structural damage is likely

Δs = Settlement difference between two points
ℓ = Distance between two points

Causes of building settlement

Often, several causes interact to lead to the observed settlement damage. Typical causes are pressure superposition and heterogeneous ground conditions (see graphics).

Other causes of settlement include:

Softening, flushing, or washing away of the building ground as a result of leaky sewer pipes and shafts, seepage of roof water, water pipe breaks, etc.
Increase in load due to building extension, garden filling, etc.
Shrinkage of cohesive soils due to drying out during long periods of hot weather
Drying out and decay of peat soils
Lowering of the groundwater level
landslide

Polyurethane in geotechnical engineering

Polyurethane (abbreviation: PUR) is a synthetic resin that is used in countless products in modern everyday life, such as household sponges, mattresses, shoes, assembly foam, etc..

PUR has been used in geotechnical engineering for soil stabilization for many decades. For example, PUR injections were already being used in German coal mining in the 1960s to secure abandoned areas and seal water-bearing layers. During the construction of the Furka Tunnel (1973–1982), PUR injections contributed significantly to solving rock mechanics problems. Since then, PUR injections have become established in tunnel construction and are also used successfully and frequently in geotechnical engineering.

Impact of polyurethane on the environment

Before the injection system presses the two-component synthetic resin system into the injection lances, the two components are mixed in a 1:1 ratio to form polyurethane at the mouth of the injection gun, which is attached to the injection lance. If the delivery pressure of the individual components differs, the injection system automatically stops delivery. This ensures that only synthetic resin in the correct mixing ratio of 1:1 is injected. When applied correctly, polyurethane has no negative impact on the environment, as confirmed by test reports from accredited laboratories.

If the soil injected with PUR is excavated and disposed of in the distant future, it can be taken to inert building material landfills, just like brick or concrete waste.

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