The sinking of the old buildings is a common phenomenon throughout Bulgaria. In addition to the many cosmetic damages that the processes of sinking of the foundations cause, they are a good cause for concern among the inhabitants. Before taking any action to resolve the issue, the following questions must be answered on a case-by-case basis:
Is the house safe for the occupants at the moment?
Is the facade safe for passing cars and pedestrians?
What causes the subsidence / sinking in question?
What is the structural damage to the house?
What measures should be taken to stop the sinking?
What fortifications are needed to restore the security of the compromised house?
How profitable is it to preserve the building?
Indirect signals for movement in the foundations of the houses are sloping doors and windows, jamming in the boxes - difficult to open and close. Visually, the processes of subsidence in the foundations are accompanied by the formation of inclined cracks on the plinth, around windows and doors, as well as oblique cracks on the inner and outer walls.
The first and most important thing in the occurrence of cracks from subsidence is to determine to what extent the condition of the structure ensures the safety of its occupants. The subsidence of the foundations inevitably reduces the security of the building you inhabit and is a prerequisite for accidents with material and human losses. Uneven sinking of parts of the foundations can form cracks in all load-bearing elements. In addition to the walls, cracks can continue in the floor slabs and columns. Another negative effect is the accumulation of additional stresses in the materials of the structure, making it more vulnerable to other impacts, especially in an earthquake.
The next potential hazards to consider when laying the foundations are the condition of the house cladding, chimneys and other elements that endanger the safety of cars and people in the immediate vicinity. Increasingly, we are witnessing traces of fallen plaster on sidewalks and the roadway. Even with small sizes, falling materials can cause great damage. According to Art. 195 of the Spatial Development Actthe responsibility is sought entirely by the owners of the collapsing property.
After determining the current state of the building and its facade elements, we proceed to discover the cause of the uneven sinking. In some cases, this is a combination of several factors.
Structural survey and geological survey
This stage is accompanied by an investment by the owners. Proper identification of the causes and selection of adequate strengthening measures are the most important parts of a project. Choosing a highly qualified design engineer can save a lot of unnecessary costs for the investor in the future. Assembling a complete engineering picture gives clarity about the value of the project and its final profitability.
Foundation in "weak" soils
Practice shows that the most common cause of such frequent subsidence is the foundation in "weak" soils. The change of the groundwater level in them activates the processes of swelling and compaction, causing cyclic movements in the foundations. The change of the water content in the soils changes their consistency and mechanical indicators.
Therefore, lowering the water level by building sidewalks and walkways around the house, drainage systems and diverting roof water away from the foundations are sometimes sufficient measures to stabilize the foundations.
In cases where these measures are implemented, but the subsidence of the foundations and cracks on the load-bearing structure continue, it is mandatory to conduct a geological survey. It can also be done in the initial stage, which in the general case saves significant funds for useless drainage activities, as well as time for the owners. The data from the geological report clearly show the composition and mechanical parameters of the soil, as well as the most optimal measures to solve the problem.
Accidents in water supply or sewerage systems
Another common cause of subsidence is accidents in the water or sewage systems near the foundations. Their localization and repair is a difficult and expensive task that requires special equipment and knowledge. The study of groundwater for high content of chlorine and other chemical elements, not typical for rainwater, is a reliable indicator of leaks from the water transmission system. In addition to raising the water level, leaks form cavities in the earth's crust, freeing up space for soil movement around and under buildings.
Construction on landslide sites
More than 1600 landslides have been registered on the territory of Bulgaria. Construction on landslides is a risky and often unprofitable endeavor. Houses built on shallow joints can be successfully fortified, unlike those built on deep joints. In the second case, drainage of large areas is the only way out.
Activation of landslide movements
Most fescue masses are affected by soil moisture and are activated in the spring from March to May or in the fall - October and November. Reconstruction and accidents in the water supply and sewerage network are also prerequisites for activation of landslide processes dictated by the human factor. The displacement of foundations and whole houses from the movements of large earth masses is characterized by its greater speed and real danger of destruction. Adequate solution of already existing movements and subsidence in the foundations can be taken only after preliminary geological studies. Determining the water horizon, the depth of the layers and their soil characteristics are the fulcrums necessary for the preparation of an effective project. Possible options are soil consolidation, drainage, construction of support facilities, pilot steps or other measures. The concept and scope of measures to stop soil movements are strictly site-specific and vary widely.
Excavation works nearby
Excavation works next to existing buildings also pose a real danger of uneven sinking of the foundations of existing buildings in the vicinity. Depending on the depth of the trench, the type of fortification, groundwater and the nature of the soil, this effect can be observed up to several tens of meters away. The rapid drainage and the lowering of the water horizon in the area of the new construction release empty cavities in the soil, which leads to its compaction and contraction. Unfortunately, these effects are difficult to avoid and usually remain at the expense of the victims.
Shallow foundation, above the freezing point, which varies from 70 to 120 cm depending on the soil and the region, is also one of the prerequisites for uneven subsidence in the foundations. This process can be explained by the cycles of freezing and thawing of water in the soil. Re-freezing and thawing of the water in the composition of the soil leads to destruction (destruction) of its integrity and opening of cavities. Another negative aspect of the shallow foundation of the houses is observed in the cases when the excavation does not reach a solid earth layer or the penetration into it is not enough. It is recommended that the foundations of the houses enter at least 40 cm into the "healthy" soil.
These are the most common causes of uneven sinking in the foundations, and of course there are others. Once measures have been taken to eliminate them, the next step is to monitor the building. In some solutions, the fortification measures do not have an immediate effect on the building. There is a gradual attenuation in subsidence and opening of cracks. Only after these processes are completely stopped is it reasonable to proceed to the restoration of lost load-bearing capacity in the structure. These activities are expressed in the filling of cracks, additional reinforcement and others.
What not to do!
Advice from acquaintances, even if they are regular civil engineers. Taking fortification measures to save a sinking building is a complex task. For its correct solution it is necessary to collect information about the type of foundation, soil characteristics, water horizon, the condition of the building. Blind execution of "heels" and framing rings very often leads to even a negative effect. The weight of the building increases significantly above the permissible for the soil. Once implemented, these measures are irreversible or extremely expensive to correct.
As a final conclusion, it can be summarized that the settlement of the foundations is a complex process with many possible causes and solutions. The research activities in the initial stage, together with the design, are the most important moments for which no money should be saved. Sometimes the sums for strengthening and drainage are high, but this should not stop the owners from taking measures to preserve their real estate and secure their houses against accidents. Postponement of building reinforcement activities leads to increased damage, significant additional costs, risks and undesirable consequences.