Geotechnical Investigation and Testing for the Petrol Station in Sustjepan (Dubrovnik)
In preparation for the construction of a petrol station with the accompanying infrastructure at the Sustjepan location in Dubrovnik, our team conducted extensive geotechnical and engineering-geological investigation and testing to ensure a reliable and safe foundation for the future traffic and maritime infrastructure project.
The site is located in the Sustjepan area, where the Ombla River meets the Adriatic Sea. The terrain is characterized by shallow fills and fluvial-marine sediments, while the subsoil consists of limestone bedrock typical of the broader Dubrovnik region.
Planned Works
The planned development includes the construction of a land-sea petrol station comprising a fuel dispenser, canopy, accompanying service facility, parking areas, and the construction and arrangement of the coastal line with the possibility of vessel mooring. Part of the intervention lies in the water area, which requires specialized understanding of the geotechnical properties of the seabed, while the land portion includes traffic and service infrastructure.
Scope of Investigation
The aim of the investigation was to determine the geological, hydrogeological, and geotechnical properties of the soil at the designated construction site. The activities carried out included:
- Geological and engineering-geological prospection;
- Rotary exploratory drilling at 4 boreholes with a total depth of 36 m;
- Engineering-geological mapping and bore core identification;
- Laboratory testing of soil and rock samples;
- Development of a geotechnical ground model.
All tests and data analyses were performed in accordance with the applicable standards (Eurocode 7, HRN EN ISO 22475-1, ASTM standards).
Geotechnical Profile
Based on drilling, laboratory tests, and field mapping, three geotechnical units were defined:
1. Fill material (GJ-1)
Fill composed of silty, poorly graded gravel with admixtures of construction debris and limestone blocks.
Thickness: 1.8 – 5.5 m
2. Marine/fluvial sediments (GJ-2)
Very soft deposits of sandy slit and clay with organic content.
Thickness: up to 2.2 m
3. Limestone (GJ-3)
Moderately to slightly weathered rock mass with a blocky structure and high joint porosity.
UCS strength: up to 89 MPa
RQD: 14 – 100%
GSI: 35 – 55
Hydrogeological and Seismic Conditions
The location lies within a zone of highly permeable carbonate rocks. Groundwater levels are directly influenced by sea tides and precipitation. Seismically, the site falls under soil class A, with a maximum ground acceleration of agR = 0.307 g (return period = 475 years), serving as the basis for earthquake-resistant structural design.
Conclusion
The obtained results provide a reliable geotechnical foundation for the main project, offering precise data on soil characteristics required for the design of foundations and execution of works in complex maritime conditions. Thorough understanding of local geological and geotechnical features will enable an optimal technical and economic execution of the future petrol station.
