Diagnostics and survey results
Work on the site began with an analysis of the initial data and a review of the design documentation. This stage is often underestimated, but it is precisely the comparison of the design solutions with the actual operational scheme that makes it possible to identify hidden prerequisites for deformations. After that, a visual inspection of the structures was carried out, during which the nature of the cracks, their orientation and relative position were recorded.
The next and key stage was the instrumental diagnostics of the foundation. To assess the condition of the soils beneath the foundations, dynamic probing was carried out at five control points. This method belongs to modern field geotechnical investigations and allows obtaining data on the density, uniformity and bearing capacity of the soil without exposing the structures. From a scientific point of view, dynamic probing relies on the patterns of propagation of impulse loads in a dispersed medium. The change in probe resistance during penetration reflects variations in soil structure, the presence of loosened zones and layer boundaries. In the context of urban development and occupied buildings, this method is an optimal compromise between information content and non-invasiveness.
The obtained data unequivocally indicated the presence of loosened soil layers beneath the foundation footing. These zones were characterised by reduced density and, as a consequence, a lower capacity to bear the load from the building. In engineering practice, such a state of the foundation is considered one of the main causes of differential settlement. It is important to emphasise that even a monolithic foundation slab is not an absolute guarantee of uniform foundation behaviour. Current research in soil mechanics shows that local heterogeneities in the mass lead to stress redistribution, resulting in flexural and shear deformations of the structure. It is precisely such processes, accumulating over time, that manifest as cracks in the above-ground part of the building.