Technical condition of buildings and common defects – structural soundness and uneven settlement of buildings
In the previous article, we acquainted you with the common defect of buildings. These defects include problems with structural soundness of the building, humidity, leakage of balconies and roofs, failures of internal and external wiring, renewal of technological equipment, insulation of the building and replacement of windows. In this article, I would like to address the issue of structural soundness of buildings and the most common defects causing uneven settlement of the building (foundation joint damage).
There are several types of foundations for buildings. Most of the buildings are usually based on foundation strips, foundation feet, all over the foundation slab, on piles (anchored in certain depth), or a combination thereof. Proper design and the construction of foundations is one of the most important phases of design and construction of the building. The load-bearing columns and walls transfer the load from the entire building to the foundation structures, which distribute this load further to the foundation joint, i.e. the subsoil under the building. When choosing foundations, several things should be kept in mind: the project, the supporting system, load-bearing structure, the geology of the subsoil and the locality in which the building will be constructed.
What are the causes of defects?
Based on long-term monitoring, we can place the causes of building structures defects into three basic groups:
Errors occurring during the project design
The design lacks quality, unsuitable load-bearing system and the type of foundation, unsuitable building materials, wrong calculations on boundary conditions.
Errors occurring during the implementation of the work
Non-compliance with technological procedures of manufacturers, the work lacks quality, non-compliance with the project design and use of different material than agreed, load placed prematurely.
Defects manifesting during use of the building
There are two subgroups: load and use of buildings different to what was intended in the design (exceeding the proposed load of ceiling tiles) and environmental effects (this includes, for example, a change in hydrogeology, weather effects, sewerage disturbances, subsoil shocks).
General principles that apply to the design of buildings and their foundation:
- The lower edge of the foundation (the foundation joint) must be located below the frost depth. The frost depth is given by the currently applicable standards. The frost depth varies depending on the location and type of foundation soil. One of the reasons for paying increased attention to the depth of foundations is the negative effects building settling might have given the changes in the bearing capacity of the subsoil. If the prescribed depth of foundation is not observed, there is a high risk of degradation of the bearing capacity of the foundation joint and uneven settlement of the building (where the subsoil of the foundations freezes during the year). In winter, the water contained in the subsoil under the foundation freezes and increases its volume, creating forces that unevenly lift the foundation joint and the foundations of the building itself. In the spring, the effect is the opposite – the frozen soil thaws, the soil settles and the foundation joint, on which the foundations are laid, sinks even further.
- The subsoil geology of the area of interest conditions the choice of the foundations type. The geological survey reveals the composition of the subsoil – a detailed analysis of the subsoil on the basis of samples taken and load-bearing capacity tests of the subsoil. Subsoil samples are taken from designated locations in several ways. The most common way to take samples is to use a probe (the choice of a suitable probe (digging and drilling) depends on the size of the planned building, the terrain and the required depth of the geological survey). The results of the geological survey give us valuable data on subsoil composition, its properties and the height of the groundwater level. The most important information the geological survey brings is the load-bearing capacity of the subsoil (usually following a dynamic penetration test).
- Shape and area of foundations. Simply put, the larger the area of the foundation through which the load is transferred to the foundation joint, the lower the probability of settling the object.
Removal of defects
In the case of defects in building’s structure, a detailed analysis of the defect is required. Foundation failures in buildings or failure to take into account the aforementioned design principles may result in the disruption of the building’s structure and endanger persons present in the building or in the near vicinity. Problems may arise even if the foundations were built properly. Changing properties of the subsoil over time may cause the building to fall unevenly and settle.
A change in the properties of the subsoil can be caused, for example, by groundwater flowing under the building (it may wash out small particles from the subsoil).
Intensive wetting of the foundation joints – rainwater from the roof of the building is not drained into the sewer or retention tank but to the foundations instead – this is a considerable problem.
Movement in the foundation joint caused by street traffic or railway traffic. Due to the above-mentioned negative impacts, the subsoil loses its original properties and uneven settlement of the building may follow. Uneven settlement of the building and movement of the foundations results in cracks in the perimeter and interior partitions, cracks in the foundation slabs, ceiling slabs and stairs.
The choice of the repair procedure, whether of the foundations or the foundation joint, must be based on a detailed survey and analysis of the defect. The analysis should be carried out by the designer or an authorized structural engineer. Subsequently, the expert proposes a detailed defect elimination technological procedure. Restoring the load-bearing capacity of a foundation joint is not an easy task. It must be done by experts in the field as they have to restore the load-bearing capacity and, in some cases, also the height of the foundation joint to the required level using a special technology and follow technical recommendations of an authorized structural engineer. Even though the repair of structurally unsound parts of the building is technically and financially demanding, it is necessary for further safe use of the building. By postponing (or totally ignoring the need) the repair of foundations or the foundation joint the already poor state of the building may deteriorate even further. For this reason, we recommend taking a responsible approach towards defects and get advice from experts in the field when considering major foundations repairs.
