Open pit protection and foundation design for the Valkane hotel
Valkane Hotel, designed by the renowned architectural studio 3LHD, is situated at a unique location within the former quarry in Pula.
In line with the architectural concept, our scope of work included the development of a geotechnical report and the main open pit protection and foundation design.
Geotechnical investigation and testing
For the preparation of the geotechnical report and subsequent design, engineering and geological as well as geotechnical investigation and testing were carried out, which included:
- geological and geotechnical exploration of the wider area;
- engineering and geological mapping of the terrain;
- exploratory drilling;
- engineering and geological logging and core analysis;
- laboratory testing; and
- analysis and interpretation of previous investigation data.
Open pit protection
Based on the geotechnical inspection of the site and the conducted investigation, it was determined that the geotechnical profile at the location is comprised of two geotechnical units: Geotechnical unit 1 (colluvium and terra rossa) and Geotechnical unit 2 (medium to weakly weathered limestones). The open pit is to be executed by forming a wide excavation with a slope of 3V:1H within the rock mass and 1V:1H within Geotechnical unit 1. The construction pit will be created on all four sides of the project boundary.
Rock excavations exceeding 2.50 m in height will be secured using Type 8 × 10 hexagonal protective mesh, while wide excavations within the colluvium and terra rossa will be protected against erosion using PE sheeting.
During the excavation of the open pit, geotechnical inspections must be conducted to identify potential instabilities such as cavities or unfavorably oriented discontinuities. In cases where cavities are identified, they will be remediated using reinforced concrete pads. For adverse rock orientations or unstable blocks, stabilization measures are to include the installation of self-drilling rock bolts and the application of shotcrete.
If required based on geotechnical site assessments, self-drilling rock bolts are to be installed in lengths of 6.0 m and 4.0 m, with a regular grid spacing of H × V = 2.0 m × 2.0 m to 2.50 m × 2.50 m, ensuring comprehensive support of the excavation faces.
Foundation and foundation soil improvement
This geotechnical project encompasses the foundation design for the hotel, restaurant, pool bar and retaining walls.
For the section of the hotel structure with a foundation on bedrock, a replacement layer consisting of mechanically stabilized crushed stone material (base layer) with a thickness of 50.0 cm is planned. In areas where the hotel foundation is within overburden layers (colluvium and terra rossa), a minimum replacement thickness of 1.0 m is proposed. This replacement comprises a geotextile layer, a stone material layer measuring 50.0 cm in thickness and a layer of mechanically stabilized crushed stone material (base layer) measuring 50.0 cm in thickness.
The foundations of the restaurant and pool bar are planned within deposits layers. Based on geotechnical investigation and testing indicating that the depth to the bedrock ranges between 4.0 m and 6.0 m, ground replacement in these areas will involve the installation of a stone material layer measuring 50.0 cm in thickness, incorporating geotextile, and a layer of mechanically stabilized crushed stone material (base layer) of the same thickness. Reinforced concrete retaining walls will be constructed within embankment material, which will be placed in layers and compacted to ensure stability.
Conclusion
After the construction of the planned structure, all horizontal loads, both static and dynamic, will be transferred to it. This project considers the protection measures of the open pit as temporary since, after the completion of the structure, the space between it and the walls of the open pit will be filled with stone material. The planned structure must also be capable of bearing all the loads that come from the surrounding soil, both under normal and seismic conditions during use, as this geotechnical project analyzed the state of protection of the temporary open pit.
