In most projects, we encountered the problem of groundwater, especially in projects that contain an underground or two floors. The groundwater is drained during the foundation stage and implementation of the lower floors by the de-watering system.
The process of draining and pumping groundwater must continue until the weight of the poured parts becomes 10% higher than the value of the up-left forces (according to the American code ACI350).
In some cases and projects in which the groundwater level is rapidly changing (an area close to the sea and the groundwater level is affected by tides, an area close to a torrent stream, and other cases) the weights of the poured elements must be 25% greater than the lifting force of the groundwater Below the base when the pumping process is stopped.
It is not permissible to stop pumping groundwater if the weight of the poured elements is less than the previously mentioned amounts.
If the lifting force is higher than the weight of the molded elements, the perforated structure will be subjected to floating. The amount of buoyancy may not be high, but it will have harmful effects.
Some of the harmful effects are the effect of insulation, the occurrence of movement or rotation in the structure, the deposition of a layer of weak sediment under the raft foundation.
The first image is a representation of the lifting force caused by the groundwater on the structure of an underground floor.
The second picture is from one of the projects that was under my management, where the groundwater level rose by 30 cm in just one week, which led to the flooding of the entire site.