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A building can subside for many reasons

Often subsidence is related to the moisture in the soil under the foundation. Some soils are more susceptible to changes in water content than others. Clay soils are particularly vulnerable because they shrink and swell in relation to their moisture content. Vegetation or large trees near the foundation can cause subsidence problems, as the roots absorb water from the ground, causing it to shrink. The risk of this happening is greatest after a long dry period when thirsty plants send their roots under building foundations in search of water. Water that leaks out of damaged sewers can sometimes soften, or even wash away the soil under the foundations. This can result in ground movement.

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Subsidence caused by compressible loam

In many areas around the world buildings are built on clay soil, which consolidates i.e. is compressible. Over time, compressible clay causes problems which can be manifested as cracks on the foundation and walls, or the building settles unevenly.

With URETEK methods one can solve the problems easily and economically, for example, by installing geopolymer pillars as a bridge between the solid foundation layer and the foundation or between a dry layer and the hard ground. They can also be used in areas with deep soil conditions as supportive cohesion pillars for the clay layers.

Subsidence caused by backfilling

Soil conditions that have not occurred naturally are called backfilled soil. This may for example be soil that has been removed from the surface of a construction site and sent to a different location. Nowadays construction authorities monitor that the backfill is used correctly. But still, one can see that under some houses there is filling soil that does not meet the quality and bearing capacity of the building's load requirements.

The backfill's behaviour is difficult to predict - because it is rarely of uniform quality it may be different from place to place. The worst case scenario is that the backfill contains organic biodegradable materials such as stumps, peat, etc. which can rot and cause problems. In some cases where there are changes in backfilling, cracks and subsidence problems occur several years later.

With URETEK methods, we can often solve the problem of backfilling more economically than other methods on the market. If necessary, you can also direct the solution to only one part of the building. 

Leaking or burst water and sewer pipes which cause subsidence problems

One of the main reasons for the foundation to be unstable is that there is a water pipe under the ground which is leaking or leaching, caused by a broken sewer pipe. The bearing capacity of soils under foundations can also deteriorate because of flowing underground channels that are further away from the building. This can lead changes in the characteristics of the soil, which may lead to subsidence of the building foundation. Similarly, water that is filtered from the ground surface into the ground - a small amount is enough - can change the properties of the soils which may cause subsidence of the foundation.

 

Inadequate groundwork

Sometimes the cause of the cracks and subsidence of the foundation are mistakes that have been made in the planning or construction phase, thereby the load calculations for the building in relation to the construction of the foundation have been calculated incorrectly. Changes in the structure that occur when extending/expanding may change the load to which the foundation is exposed and lead to problems. Subsidence, tensions and deformations and cracks in structures can, depending on the object, either occur on the new extension, or on the old part of the building.

Sometimes noticeable damages can be seen after several years. Sooner or later, it pays to improve the ground properly.

Excavation near a building causing subsidence in the ground

Careless excavation near buildings can cause ground rupture, especially when soils are granular (sand, gravel or silt). Foundations built on clay soil can be affected by excavations carried out up to tens of meters away.

Settled floors

Often a building is on a solid foundation, but the floors are left floating. This leads to floor settlement. URETEK methods are in many cases an economical solution for improving and re-levelling the floor.

Vibrations from heavy traffic 

Sometimes the cause of the subsidence is found to be from the neighbouring plot or from a nearby highway. Vibration caused by heavy traffic or piling performed on a neighbouring site may lead to badly or loosely packed soil packing together further, which may lead to subsidence of the building.  

Poorly packed backfill always subsides

2 metre deep loosely packed backfill soil can subside under a building's weight by as much as 10cm. 

Common causes of subsidence

  • The building or structure has been built on compressible clay soil
  • Soil under the building/structure has not been compacted properly during construction
  • Water damage has weakened underlying soil and foundations
  • Movement of varying soil structures underneath foundations
  • Vibrations & moving of soil at nearby excavations
  • Vibration from passing traffic
  • Incomplete/poor quality foundation works
  • Changes in environmental or surrounding circumstances