Deep foundation design for the building in Slovenia
For the purpose of constructing a commercial building in Slovenia, a deep foundation design was undertaken at the location designated for the extension of the facility. The wider area of the site is partially developed, while the undeveloped portion consists of agricultural land.
For the planned extension on the northern side, this project defines the foundation method for the future structures. Considering their structural system and the varying distribution of loads, the design includes isolated footings, strip footings, and foundation slabs. The isolated and strip footings will be founded deeply using reinforced concrete piles, arranged in grids and with lengths determined by calculations and shown in the project’s graphical documentation.
Geotechnical investigation and testing
For the purpose of developing this main design, previously made geotechnical investigation and testing were used as a basis. In addition, we have carried out additional geotechnical investigation and testing, which included:
- Geological and geotechnical prospecting of the wider area
- Engineering and geological terrain mapping
- Super Heavy Probe Dynamic Penetration (DPSH) Tests
- CPTU Tests
- Processing data from previous research and correlation with new data
Based on the conducted investigation and testing as well as the reinterpretation of earlier research in the wider area, the geotechnical report was prepaired and served as a geotechnical basis for this main geotechnical design (deep foundation/piloting design).
Foundation
The foundation includes three new structures. Depending on the load distribution and the type of load-bearing elements, the foundations are designed as follows:
1. Columns of the structures are founded on isolated spread footings, whose foundation system is divided into three types, depending on the length and number of piles on which they are supported. All piles are constructed with a diameter of D = 600.0 mm.
2. Walls of the structures are founded either on strip footings or on foundation slabs, which are also supported by reinforced concrete piles with a diameter of D = 600.0 mm, arranged in a grid as shown in the project’s graphical documentation.
The types of isolated footing foundations are described below:
Type 1 is installed beneath columns with the highest loads, as shown in the project drawings. It consists of a pile cap (isolated footing) with a thickness of d = 0.85 m (structural design) and plan dimensions of 3.50 × 3.50 m. The pile cap is connected to six reinforced concrete piles with a diameter of D = 600.0 mm and a length of L = 12.0 m, arranged in a regular grid of 1.75 m × 1.17 m.
Type 2 is installed beneath columns with “medium” loads (in a global sense), as indicated in the project drawings. It consists of a pile cap (isolated footing) with a thickness of d = 0.60 m (structural design) and plan dimensions of 3.0 × 3.0 m. The pile cap is connected to four reinforced concrete piles with a diameter of D = 600.0 mm and a length of L = 8.0 m, arranged in a grid of 1.80 × 1.80 m.
Type 3 is installed beneath columns with lower loads (in a global sense), also as shown in the project drawings. It consists of a pile cap with a thickness of d = 0.60 m and plan dimensions of 3.0 × 3.0 m. The pile cap is connected to four reinforced concrete piles with a diameter of D = 600.0 mm and a length of L = 5.0 m, arranged in a regular grid of 1.80 × 1.80 m.
As part of the calculations for mechanical resistance and stability, the vertical bearing capacity of reinforced concrete (RC) piles was determined. In order to verify the adequacy of the designed solutions, testing of all constructed piles is envisaged to ensure that their characteristics comply with the project requirements.
Conclusion
Given the dimensions and scope of the project, calculations of the bearing capacity and settlement of the foundation soil were carried out. These analyses used soil parameters obtained from previous and additional geotechnical investigations and testing.
Based on the performed calculations, taking into account the size of the structures and the loads they transfer to the foundation soil, three different types of isolated footings were determined for supporting the columns of the structure, while the walls are founded on strip footings or on foundation slabs, which are also placed on reinforced concrete piles with a diameter of D = 600.0 mm.
Prior to the construction of the foundation structures, the foundation soil is prepared by placing a layer of crushed stone material and sub-base (granular fill) beneath them to reduce future settlements.
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