To the most dangerous in the aftermath, and sometimes the most difficult to control causes causing the destruction of monuments are these, caused by changes in the natural environment, with which the object is permanently connected, especially in the case of violation of the natural stability of the terrain and subsoil.
The transformation process can be very complicated and often difficult to explain due to unidentified or anomalous phenomena occurring slowly in the subsoil.
On the basis of the previously disclosed cases and causes of damage to historic buildings in connection with the condition of the ground, it can be observed, that violations of the strength and operational suitability of soils are caused mainly by the following phenomena:
A. Anomalnych cech gruntu, which cause periodic movements of the ground. Cohesive soils in particular are characterized by these features (loams, cops, lessy, dusts). In this case, these phenomena are especially strongly influenced by changes in humidity and climatic fluctuations.
Excessive soil moisture most often occurs in connection with the damming up of watercourses during sudden or prolonged precipitation, in the event of leaks in the sewage and water supply networks. In this state in macroporous soils, with stress concentrations under the foundations, collapse occurs, resulting in uneven settlement of individual parts of the building or collapse of foundations, and, consequently, the formation of scratches and cracks in the walls and other structural elements of the building.
B. Specyfiki pracy i deformacji gruntu pod budynkiem na skutek niekorzystnej konfiguracji fundamentów i nieprzystosowanej konstrukcji.
In this case, buildings with an elongated or broken outline have a particularly unfavorable effect on the stresses in the ground, or having an incorrect shape of foundations, or having a statically unbalanced body system, resulting in ground displacement due to uneven compression.
C. Niewłaściwej eksploatacji terenu w zasięgu budowli, As a result, the natural properties of the soil are violated and unfavorable conditions are created for the building and its surroundings, np. as a result of leveling the area or making embankments, destruction of greenery and forests, improper ground and underground exploitation.
These phenomena occur especially in some regions of Poland in areas within the range of old and new underground excavations. In this case, as a result of tectonic movements, a subsidence trough is formed over the collapsing excavation, causing a change in the configuration of the terrain: concavities are formed, bumps and ground creep, resulting in an imbalance of earth masses and, as a result, serious damage to buildings, and even a disaster.
Cracking and displacement of individual parts of masonry buildings also occur in the area of old urban districts as a result of the collapse of previously existing underground structures (np. multi-level cellars, pass, channels, etc.).
D. Zmiany warunków hydrogeologicznych na Skutek zachodzących przeobrażeń w przyrodzie, conscious or unconscious activity of man or others, unpredictable reasons.
Particularly dangerous phenomena that have a destructive effect on the ground include lowering the groundwater table or changing the direction of their flow. In the first case, the phenomenon occurs most often as a result of changes in water relations in the vicinity of the historic building, np. related to the regulation of rivers and streams, destruction of the irrigation system of defensive devices, etc.
Changing the water ratio or humidity has a very negative effect on the strength properties of the substrate under the foundations. In many soils, as a result of water flow or their oscillations, fine and dusty parts are washed away. These processes entail changes in the soil structure and, consequently, a loss of initial strength.
A similar phenomenon occurs in wet or saturated ground with high standing groundwater during freezing. Under the influence of freezing and, in turn, thawing, significant deformations occur in the ground, which is very harmful to the foundations and underground parts of the building structure.
slow, but a gradual disturbance of the balance of earth masses may also be caused by the geological structure of the area, which favors this phenomenon, and by a periodic increase in precipitation. Groundwater is disturbed in irrigated areas, disturbance of the terrain balance, its cracking and, consequently, the formation of sliding movements.
Paying attention to the foundation conditions in the process of investigating the causes of damage to masonry buildings is of great importance. It turns out, that the above-mentioned phenomena affect damage in different ways, although the effects are apparently similar. In connection with, analyzing the causes of damage, it is necessary, at least in general terms, to know the circumstances of the occurrence of these phenomena. These issues are very specific and in essence fall within the scope of engineering geology, hydrogeology and soil mechanics, therefore, it is difficult to explain them exhaustively here.