Slope and rockfall protection – the ZVIR complex
Works on the slope and rockfall protection at the Zvir Complex in Rijeka have been completed. For this project we have carried out engineering geological and geotechnical investigation and testing and made the detailed slope and rockfall protection design.
The supervision of protection works we performed included the analysis and verification of the situation in the field, as well as adjustments of the design.
The concerned slope micro-location at the Zvir Complex sits in the northwestern part of the right bank of the Rječina riverbed, at the end of Vodovodna street, behind a building complex along the access road to the Zvir Complex. It is presented as a steep to subvertical slope of approximately west-east extension. The steeper parts of the slope are presented as bare rock mass, while the more moderately steep parts are overgrown with low vegetation and sparse trees. In the slope area there are several low walls made of stone blocks. The base of the slope is completely built in the form of existing buildings and paved surfaces. The altitude of the terrain is approximately 8.0 m above sea level at the foot of the slope and up to 95.0 m above sea level at the location of the existing rockfall protection barrier under the Rijeka bypass.
Over time rockfall of smaller rock blocks was observed at the location, endangering the users of the access road to the complex. The execution of works began in March 2021 and was completed in May 2021.
Geotechnical investigation and testing
For the purpose of the construction execution design (the geotechnical part) for slope and rockfall protection, observation points were recorded at the positions of engineering geological measurements and local engineering geological conditions were determined. In addition, we have carried out engineering geological mapping, geological prospecting of the wider area, geotechnical prospecting of the location and data processing of the previous investigation.
The geotechnical and engineering geological investigation and testing were carried out in March 2017. Additional engineering mapping at the location was conducted in March 2020.
In the scope of slope and rockfall protection, works were planned to increase slope stability and rockfall protection. Slope protection included the installation of the following protection measures:
- protection of unstable blocks by installing anchors;
- rod anchors;
- protective mesh;
- installation of rockfall protection barriers.
Before beginning the works on slope protection, the area was cleared of vegetation, shrubs and trees, as well as clay, rocks and loose blocks using blowing air under pressure.
After the clearing, the positions of slope protection measures on the basis of project data were staked and marked (height and position).
In order to prevent the collapse of rockfalls, slope protection was performed by installing a protective galvanized double-twisted hexagonal wire mesh Type 8×10. The mesh was additionally reinforced with concrete weights at its bottom. The weights are made of concrete of compressive strength class C 25/30, dimensions 30x30x10 cm.
On a part of the slope, an unstable rock block was anchored by installing rod anchors (minimum diameter Φ = 32.0 mm) made of steel B 500B, length L = 3.0 and 6.0 m. Rod anchors were installed in the potentially unstable rock block. The anchors have a base plate that adheres to the face of the slope. They are installed at least 10 days after the injection and are tightened to a force of P0 = 50.0 kN.
The protection against possible future rockfalls included the construction of rockfall protection barriers B-ZVIR-1 and B-ZVIR-2 with potential energy absorption (energy capacity) of 1000.0 kJ.
After the vegetation was removed, the geodetic staking out of the barrier pillars was conducted. Based on the inspection of the staking and a better insight into the situation in the field and in agreement with the investor, the designer and the contractor, and also in accordance with the detailed technical instructions of the manufacturer for each barrier, the exact location, spacing and barrier length for rockfall protection was determined.
The length of the constructed B-ZVIR-1 barrier is 40.0 m, and the length of the constructed B-ZVIR-2 barrier is 36.0 m. The length of the constructed barriers for rockfall protection is a total of 76.0 m.
The works at the location lasted approximately 3 months and were finished within the contractual deadline, in accordance with the contractual obligations. In addition, the works were conducted in accordance with the contractual cost statement and the requirements of the investor.