Hotel Panorama – Geotechnical investigation and testing and open pit protection design
In the southeastern part of the town of Opatija, the reconstruction and extension of the Panorama Hotel is planned. As part of this reconstruction and extension, we participated in the development of the open pit protection design. The architectural design is sign by mataija x sipina x turato.
Existing condition of the building
The existing building was constructed in 1965 and is currently not in use. Its outer shell is damaged, and some parts of the building are open. Since it is located approximately 300 meters from the sea, there is uncontrolled accelerated deterioration of the structure.
Because of the project’s specificity and complexity, and the fact that the building is an individual cultural heritage monument, the description of the reconstruction and extension is provided in zones.
Zone A — “Central Building”
Because of its extremely poor existing condition, part of the building will be demolished and replaced with new construction. For this reason, some of the adjacent walls will be supported, and careful excavation with protection will be required along the existing parts of buildings K and B. Compared to the existing condition, excavation is planned to a depth of 1 to 2 floors.
Zone B — “Shop and Cinema”
An existing part of the building. The reconstruction of this part is planned (reinforcement to achieve earthquake resistance).
Zone C — “Staircase and Gym”
A part of the structure that did not exist before, consisting of one semi-buried floor. It will be constructed by excavation directly adjacent to the existing part of building B to a depth of 1 floor.
Zone D — “Pool”
A new part of the structure, separated from the rest of the building. The excavation floor level is the same as for zone C.
Zone E
A new part of the structure consisting of one above-ground floor.
Zones F and G — “Canopy, Reception and Elevator”
A new part of the structure (covered vehicle and pedestrian entrance canopy, reception and two elevator shafts). The reception is a ground-level structure and the elevator descends to lower floors. The elevator shaft extends to level -1 and minimal excavation is planned, directly adjacent to the existing part of the building K, to a depth of about 1.0 meter.
Zone H — “Apartments”
A new part of the structure with one semi-buried and one above-ground floor.
Zone I — “Annex”
The reconstruction of this part of the building is planned (reinforcement to achieve earthquake resistance).
Zone J — “Pedestrian Tunnel”
A new part of the structure connecting a part of building H with a part of building A.
Zone K — “Rooms”
An existing part of the building. The reconstruction of this part is planned (reinforcement to achieve earthquake resistance).
Geotechnical investigation and testing
To prepare the geotechnical report and open pit protection design, geotechnical investigation and testing were conducted, which included:
- Geological and geotechnical prospecting of the wider area
- Exploratory rotary drilling
- Engineering geological terrain mapping and core sample determination
- Standard Penetration Test (SPT) investigations
- Laboratory testing
- Data analysis from previous investigations and correlation with new data
Open pit protection design
For the reconstruction and extension of the hotel, it is necessary to carry out excavation into the existing terrain down to approximately 7.50 m (measured from the existing ground level). According to the results of the survey works, the excavation of the open pit will be partially within the fill and partially within the bedrock.
For the reconstruction of a part of building A and for the construction of the newly planned parts of buildings C, D and F, excavation is required directly adjacent to the existing parts of buildings K and B. Because of the lack of adequate space between the existing and the newly planned parts of the building, a vertical excavation is planned with additional safety measures. In the southeastern and northwestern parts of the site, near the property boundaries, for the purpose of constructing the newly planned parts of buildings C, D and F, temporary protection of the open pit is planned, carried out with vertical excavation and sloped excavation. For the rest of the site, where the newly planned buildings are to be constructed, a wide excavation in a stable geometry is planned within the fill and bedrock. The excavation within the fill is planned with slopes of 1V:1H, 1V:1.25H and 1V:1H (depending on the excavation height). The open pit, considering the planned excavation safety measures, is divided into six zones.
Zone 1 of the open pit extends between the existing part of building K and the reconstructed part of building A, with vertical excavation over two floors, totaling a height of 6.30 meters. Temporary protection of the upper excavation floor is to be provided by the construction of a pile wall made of micropiles with a diameter of 330.0/310.0 mm and a length of 5.70 meters. The micropiles are to be installed with a spacing of 0.75 meters. The reinforcement for the micropiles is to consist of IPE 220 steel profiles made of S 235 steel, with a length of 6.0 meters. The micropiles are to be connected at the top with a reinforced concrete cap beam of dimensions 0.55 × 0.33 meters, made of concrete with a compressive strength grade of C 30/37.
For additional protection of the pile wall, the installation of one row of self-drilling anchors with a minimum diameter of 32.0 mm through the reinforced concrete cap beam is planned. The self‑drilling anchors are to be installed with a length of 6.0 meters, an anchor length of 4.0 meters, at an inclination of 20° from the horizontal. The spacing between the anchors is to be 2.25 meters. Shotcrete is planned to be applied in two layers, each 5.0 cm thick, with Q-188 reinforcement mesh on the face of the pile wall to prevent material sloughing between the micropiles. Temporary protection for the lower excavation floor is to be provided by shotcrete applied in two layers, each 5.0 cm thick, and one layer of Q-188 reinforcement mesh, combined with one row of self-drilling anchors with a minimum diameter of 32.0 mm and a length of 4.0 meters, installed horizontally with a spacing of 2.25 meters and an inclination of 20° from the horizontal.
Zone 2 of the open pit covers the area of the reconstruction of a part of building A, with vertical excavation to a depth of approximately 5.0 meters. The installation of shotcrete is planned in two layers, each 5.0 cm thick, along with one layer of Q‑188 reinforcement mesh, in combination with two rows of self-drilling anchors with a minimum diameter of 32.0 mm, with lengths of 3.0 and 4.0 meters, on a general grid of 2.50 × 2.0 meters (H × V), at an inclination of 20° from the horizontal.
Zone 3 of the pen pit extends between the existing part of building B and the reconstructed building A, with vertical excavation to a depth of approximately 4.0 meters. The installation of shotcrete is planned in two layers, each 5.0 cm thick, along with one layer of Q‑188 reinforcement mesh, in combination with two rows of self-drilling anchors with a minimum diameter of 32.0 mm, with lengths of 3.0 and 4.0 meters, on a general grid of 2.50 × 2.0 meters (H × V), at an inclination of 20° from the horizontal.
Zone 4 of the open pit covers the area between the existing part of building B and the newly planned part of building C, with vertical excavation to a depth of approximately 4.0 meters. The installation of shotcrete is planned in two layers, each 5.0 cm thick, along with one layer of Q‑188 reinforcement mesh, in combination with two rows of self-drilling anchors with a minimum diameter of 32.0 mm, with lengths of 3.0 and 4.0 meters, on a general grid of 2.25 × 2.0 meters (H × V), at an inclination of 20° from the horizontal.
Zone 5 of the open pit covers vertical excavation along the newly planned part of building D, near the property boundary, over two floors, with a total height of 6.40 meters. Temporary protection for the upper excavation floor is to be provided by the construction of a pile wall made of micropiles with a diameter of 330.0/310.0 mm and a length of 5.70 meters. The micropiles are to be installed with a spacing of 0.50 meters. The reinforcement for the micropiles is to consist of IPE 220 steel profiles made of S 235 steel, with a length of 6.0 meters. The micropiles are to be connected at the top with a reinforced concrete cap beam of dimensions 0.55 × 0.33 meters, made of concrete with a compressive strength grade of C 30/37. For additional protection of the pile wall, the installation of one row of self-drilling anchors with a minimum diameter of 32.0 mm in two rows is planned. The self-drilling anchors will be installed with lengths of 6.0 and 8.0 meters, an anchor length of 4.0 meters, at inclinations of 20° and 25° from the horizontal. The spacing between the anchors is to be 2.0 meters and the vertical spacing is to be 2.0 meters and 1.50 meters. The upper row of the self-drilling anchors will be installed through the reinforced concrete cap beam, while the lower row will be installed through horizontal steel beams formed from 2 UPN 140 profiles (S275 steel). Shotcrete is planned to be applied to the face of the pile wall in two layers, each 5.0 cm thick, with Q-188 reinforcement mesh, to prevent material sloughing between the micropiles. Temporary protection for the lower excavation floor is to be provided by shotcrete applied in two layers, each 5.0 cm thick, with one layer of Q-188 reinforcement mesh, combined with one row of self-drilling anchors with a minimum diameter of 32.0 mm, a length of 4.0 meters, installed with horizontal spacing of 2.25 meters and 2.50 meters (only in the zone where the pile wall is above it). The anchors will be installed with an inclination of 20° from the horizontal.
Zone 6 of the open pit covers the excavation with a slope of 2V:1H (within the embankment) for the platform east of the building, along the boundary of the property, to a height of up to 2.50 meters. Shotcrete is planned to be applied in two layers, each 5.0 cm thick, along with one layer of Q-188 reinforcement mesh. For drainage of any seepage water behind the shotcrete surface, the installation of geocomposite strips is planned, with a spacing of 2.0 meters (for vertical excavations) and 3.0 meters (for excavations with a slope).
Conclusion
This project considers the open pit protection measures as temporary. The structure of the future building must be able to withstand all loads from the surrounding soil (for both permanent and seismic design situations) during the use of the building, as this geotechnical design only analyzes the condition of open pit protection. After the construction of the future building, all horizontal loads (both static and dynamic) will be transferred to it.
