A small lowering of groundwater level leads to weaker house foundations, says Study

According to research done at the University of Gothenburg, a small lowering of the groundwater level can destroy the foundation of a house. The thesis shows that wooden pile foundations show visible damage after only a year if the groundwater level lowers. Johanna Elam conducted research to find it out.

According to research done at the University of Gothenburg, a small lowering of the groundwater level can destroy the foundation of a house. The thesis shows that wooden pile foundations show visible damage after only a year if the groundwater level lowers. Johanna Elam conducted research to find it out. Many old buildings in Gothenburg were constructed on foundations of wooden piles. According to the research, as long as the piles are surrounded by waterlogged, wet clay, they are very durable but when the mud starts to dry out, soft rot fungi attack the piles, which eventually lose their bearing capacity, and this leads to the progressive settlement of the buildings.

Speaking about the study, Researcher Johanna Elam said, "I wanted to investigate how quickly new local groundwater conditions affect the degradation of the wood in clay soil. We have been able to show that soft rot fungi only grow above the groundwater level and that bacterial degradation is less the further below the groundwater level the wood lies." To conduct the research, she investigated wooden piles and measured the environmental conditions under eight buildings in Gothenburg. In addition, she simulated a range of groundwater conditions in laboratory experiments to better understand the effects of a lowered water table.

After examining, Johanna said, "In lab experiments, I saw that degradation is already visible on wooden piles after 12 months where the groundwater level had been lowered and the surrounding clay was no longer waterlogged. The samples taken from the piles under the buildings have all managed to escape rot, which indicates that the groundwater level and the anoxic environment have been maintained over time." She added, "Today, a fall in the groundwater level of no more than 30 cm around construction sites is often a requirement. However, a 30 cm fall in the groundwater level can be enough to cause serious damage to a wooden pile if the fall occurs over a long period of time. The worst degradation of the wood occurs just above the surface of the water table, although it takes quite a long time for oxygen to penetrate down into a clay soil that has dried out."

Lastly, giving a pro-tip to the owners of the buildings, Johanna concluded by saying that one should take samples of existing wood foundations before a construction project starts on a neighbouring property so one can assess the extent to which the wood is already degraded and how protective the environment is. (ANI)

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