Rockfall and slope protection on state road D66, section 003, from km 15+000 to km 23+000
Works on rockfall and slope protection on state road D66, section 003, from km 15+000 to km 23+000 are completed. We have carried out the engineering geological and geotechnical exploration and investigation works and made the main and detailed rockfall and slope protection design.
In addition, we have carried out the engineering supervision which included the analysis and verification of the situation in the field.
This section of the state road D66 stretches from the village of Brseč in the south to the municipality of Mošćenička Draga in the north, along the eastern slope of the Učka ridge. The existing road was constructed mostly by cutting into the existing terrain, with some parts constructed by backfilling. Numerous slopes up to 16.0 m high were opened by cutting. The slopes are mostly on the left side of the road, subvertical to a steep slope towards the south, southeast, east and northeast, and are mostly bare (not overgrown with local vegetation).
The works began in November, 2019 and were completed in April, 2020.
The protection of the whole section as planned in the project documentation was conducted. The remediated section is 7.6 km long.
Geotechnical exploration and investigation works
We have carried out the engineering geological mapping, slope categorization, geological prospecting of the wider area, geotechnical prospecting of the location and data processing of previous research for the (the geotechnical part) main and detailed rockfall and slope protection designs.
Geotechnical and engineering geological works were conducted in May and June, 2018.
Protection measures
As part of the rockfall and slope protection, works to increase slope stability and rockfall protection were planned. Rockfall and slope protection included the following protection measures:
- removal of unstable blocks,
- underpinning the building walls with mortar and stone blocks,
- installing rock bolts,
- installing self-drilling anchors,
- installing protective mesh,
- installing protective mesh reinforced with steel ropes,
- slope protection with shotcrete,
- installing rockfall barriers.
Before implementing the rockfall and slope protection, the slope was cleared of vegetation, clay, stones and loose blocks up to 50.0 kg (by blowing under pressure).
At positions P-01_L and P-02_D, instabilities were observed in the form of rockfall blocks of approx. 0.5 m3 loosened by bioerosion and atmospherics. The protection was conducted 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.
At the position P-33b_L, instabilities were observed in the form of rock blocks of approx. 1.0 m3 loosened by bioerosion and atmospherics and rockfall in overhangs. The protection was conducted by removing the unstable blocks and 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.
At the position P-10_L, instabilities were observed in the form of rockfall blocks up to approx. 0.5 m3 loosened by bioerosion and atmospherics and overturning and rockfall of rock mass in the overhang, up to approx. 5.0 m3. The protection was conducted by underpinning the unstable parts of the slope and installing New Jersey concrete bumpers along the edge of the road.
At the position P-14c_L, instabilities were observed in the form of rockfall blocks of approx. 0.5 m3 loosened by bioerosion and atmospherics. The protection was conducted by installing rock bolts of Ø 32 mm, L = 3.0 m, a protective mesh and steel ropes. A galvanized double-twisted hexagonal wire mesh Type 8×10 was additionally reinforced with steel ropes of Ø 12.0 mm. Steel rope is placed diagonally in both directions and vertically, and is fastened with specially shaped anchor plates.
At the position P-27c_L, instabilities were observed in the form of rock blocks up to 1.0 m3 loosened by bioerosion and atmospherics, planar faults, overturning and rockfall of rock mass in the overhang. The protection was conducted by installing rock bolts of Ø 32 mm, L = 3.0 m. In addition to the bolts, a protective mesh and steel ropes were installed. A galvanized double-twisted hexagonal wire mesh Type 8×10 was additionally reinforced with steel ropes of Ø 12.0 mm. Steel ropes are placed diagonally in both directions and vertically, and are fastened with specially shaped anchor plates.
After the removal of vegetation during supervision, a better insight into the situation in the field was gained and it was decided that the location around the part of the slope with a high shelf shall be protected by installing a rockfall barrier. It was constructed as protection from the fall of smaller unstable blocks from the top of the shelf, and the barrier, H = 1.85 m and L = 35.0 m, was installed to protect against falling debris.
At the position P-27b_L, instabilities were observed in the form of erosion of parts of the rock mass and rock blocks in the overhang. Slope protection was conducted by injecting shotcrete, installing reinforcing mesh and self-drilling anchors of Ø 32 mm, L = 3 m. Shotcrete is set in two 5,00 cm layers with one layer of Q 188 reinforcing mesh between them. In order to eliminate possible hydrostatic pressure behind the shotcrete, drains of L = 2.0 m are made using perforated hard PVC or similar material pipes with a minimum diameter of 50.0 mm.
Conclusion
The works took approximately 5 months and were conducted within the contractual deadline and in accordance with the contractual obligations, in the sense of the cost estimate and the investor requirements. The protection of the whole section as planned in the project documentation was conducted. When choosing protection measures, we tried to use shotcrete as seldom as possible in order to fit the remediated slope into the natural environment. The remediated section is 7.6 km long.
Read more: Protective mesh, Rockfall barriers
