Published on: 2026-09-28
Source: Saint Petersburg State University of Architecture and Civil Engineering –
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At the Saint Petersburg State University of Architecture and Civil Engineering, a study was conducted on how contamination of sandy soils with petroleum products affects their properties and, consequently, the performance of building foundations. The results allow for consideration of the consequences of pollution when designing foundations in areas of oil depots, oil terminals, gas stations, and other sites where there is a risk of petroleum product spills.
The study was conducted by a senior lecturer of the Department of Geotechnics, Candidate of Technical Sciences Alina Kvashuk. The scientific supervisor of the work was a professor of the geotechnics department, Doctor of Technical Sciences Rashid Mangushev.
From an environmental problem to the calculation of foundations
The penetration of petroleum products into sandy soil can occur, for example, during a leak from a tank, damage to its bottom, or a spill during transportation. This changes the physico-mechanical properties of the soil: its filtration characteristics and internal friction angle decrease, and compressibility increases.
For the structure, this may mean a reduction in the bearing capacity of the foundation, an increase in foundation settlements, and a longer period for their stabilization.
Earlier studies of soils contaminated with petroleum products were mainly related to engineering-geological and environmental assessments, including reclamation issues. In the SPbGASU study, sandy soil was considered directly as the foundation of a structure. This allowed establishing quantitative relationships between contamination characteristics and changes in soil properties, and then using the obtained data in foundation calculations.
What happens to sand when it is polluted
The study examined the impact of three types of petroleum products – A-95 gasoline, diesel fuel, and heavy oil – on sands of various grain sizes: from coarse to dusty. The concentration of petroleum products ranged from 0 to 12% by mass.
Experiments showed that under the influence of petroleum products even the granulometric composition of sand changes. In the soil, dispersion processes occur — the splitting of particles into smaller ones, and aggregation, that is, their sticking together into larger formations. Dispersion is predominantly characteristic of coarse and medium sands, while aggregation occurs in silty sands. The most intense particle splitting was observed under the influence of gasoline, and aggregation — when silty sand was contaminated with heavy oil.
At the same time, the soil’s permeability to water decreases. Depending on the sand’s coarseness, the type of petroleum product, and its concentration, the filtration coefficient decreased by 11–99%. For example, fine sand became impermeable to water when the diesel fuel content was 10–12%, and in the case of contamination with heavy oil, it became slightly permeable to water at a concentration of 6%.
The study also revealed significant changes in strength and deformation properties. The internal friction angle decreased by 5–22%, and the oedometer deformation modulus decreased by 40–85%. At the same time, with heavy oil contamination, the specific cohesion could increase up to ten times.
The most noticeable changes occurred at petroleum product concentrations up to 6%. Further increases in concentration led to an additional decrease in some properties by no more than 10%.
Pollution affects foundation settlements
The obtained characteristics were used to assess the behavior of the foundations of the structures. The calculations showed that the design bearing capacity of the soil may decrease by 10–40%, and the ultimate settlement of the foundation may increase up to eight times. At the same time, the settlement stabilization period in some cases can reach 17.5 years.
To verify the results, the researchers conducted numerical modeling using the PLAXIS 3D software package. A tank with a volume of 20,000 cubic meters with a locally contaminated soil area and an oil product seepage depth of 7 meters was considered. The modeling showed that the unevenness of the settlements exceeds the limit values according to regulatory criteria for all three studied oil products.
Thus, oil contamination of sandy soil can affect not only the environmental condition of the area but also the reliability of the foundation of the structure. During design, it is necessary to consider a reduction in the ultimate soil pressure by 17–60%, a possible increase in settlements, and a longer time for their stabilization.
“When calculating foundations according to ultimate limit states, it is necessary to take into account a reduction in the ultimate bearing pressure on the foundation soil by 17–60%, depending on the grain size of the sandy soil, the type of petroleum product and its concentration, a reduction in the design soil resistance, the probability of additional settlements developing that exceed the calculated value by several times, as well as an increase in the settlement stabilization time of the foundations,” notes Alina Kvashuk.
Practical application of the results
The developed recommendations are intended for use in the design of foundations on sandy soils subject to oil contamination. They may be of interest to design and construction organizations, as well as specialists involved in the inspection of emergency tanks and the analysis of causes of uneven settlements.
The results of the work have already been applied by JSC “Trust No. 68” in the construction of foundations on the territory of the St. Petersburg oil terminal and at the site of the St. Petersburg container terminal.
In the future, researchers plan to expand the list of studied pollutants to include fuel oil, motor oils and their mixtures, as well as shift from homogeneous sandy bases to multilayered and heterogeneous soil masses typical for real construction sites. Another direction is refining the calculation models for soils whose properties under the influence of petroleum products begin to approach those of cohesive soils.
The news is published based on the results of the execution of the SPbGASU 2026 grant.
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