When determining the probable cause of crack formation, we may be dealing with a stable crack ; damage that has not developed further (caused by shrinkage and creep) or an unstable crack ; damage that is developing further (e.g., due to foundation subsidence). In these cases, the cause must first be eliminated before a proper repair can be carried out.
As the groundwater level drops, the soil settles. This can lead to negative friction in pile foundations, pulling the piles downward.
Also, when the groundwater level drops, a current can occur that carries soil along, resulting in a landslide.
Finally, due to a lowering of the groundwater level, wooden poles may suddenly come partially above the water level (the phreatic surface), causing them to rot.
Lowering of the groundwater level can be caused by:
Due to excessive water inflow, water can no longer drain through the ground, creating a more or less quicksand-like structure. The granules will seek a denser packing, causing the building to settle, resulting in cracks.
Increased groundwater level can be caused by:
Localized ground raising creates uneven ground loads . For example, when paving is periodically raised, the piles on the facade side are subjected to additional loads, increasing the negative friction (layers of soil, as it were, cling to the piles). This causes the building to tilt toward the street.
A landfill causes a drop in the original ground level.
Stresses can be distributed through the ground in such a way that it is pushed up in another place.
Vibrations can cause the ground to settle locally.
Vibrations can be caused by:
Cohesive soils are highly compressible, such as clay and loam . Due to the associated poor permeability of these soil types, settlements sometimes take decades to reach their final value.
Non-cohesive soils are generally very low-cohesion soils, such as sand and gravel. These soils are relatively permeable to water and have low compressibility. Final settlement is reached quickly. The rate of settlement is therefore related to the soil's permeability to water.
Causes of damage due to (failure to take into account) geological conditions:
Common design and implementation errors:
In a standard single-family home, the weight of the excavated soil for the basement exceeds the weight of the building that will take its place. Therefore, settlement in the basemented section is usually zero. However, settlement (and therefore damage) will occur under the non-basement section.
Roots from trees that are too close to the building can push up the foundation of buildings with shallow foundations . The tree roots locally extract water from the ground, lowering the water table. The cracks will be open in summer and closed/smaller in winter. The size and type of tree play a significant role in daily water consumption.
Foundation subsidence is usually a slow but continuous process, with the crack reappearing after a longer or longer period. Unfortunately, it's not easy to determine whether the situation has stabilized or not. Sometimes, an indication can be obtained by asking questions:
In the case of a structural foundation problem, something will have to be done to the foundation.
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