Kosavin Landslide Remediation on the 5062 County Road
In the village of Kosavin of Primorje-Gorski Kotar County, a landslide has occurred along the 5062 county road, approximately 37.0 meters wide and 25.0 meters long, on the southern roadside. The landslide is characterized by a frontal crack approximately 3.0 m high. In some parts, the landslide has the properties of a mud flow, and with its failure surface, it has engulfed and damaged the existing road culvert.
Furthermore, on the northern side of the site, there is an additional smaller landslide measuring approximately 12.0 meters in width. Fortunately, this landslide did not impact the road itself.
The material sliding at the site is primarily attributed to a combination of insufficient drainage and culvert capacity, exacerbated by heavy rainfall that initiated the sliding process.
Geotechnical investigation and testing
For the landslide remediation design, we carried out engineering, geological and geotechnical investigation and testing. These works consisted of prospecting a wider area, mapping the terrain and exploratory drilling. In addition to the above, further investigation was carried out, which included determination of drill cores, standard penetration tests (SPT) and laboratory tests.
As part of the exploratory drilling, three boreholes (B-1, B-2 and B-3) were drilled in the field, each 15.0 m long. By processing all the data, we created a geotechnical report that served as a basis for a further landslide remediation design. The geotechnical report provided insight into the appearance and dimensions of the sliding surface, as well as the materials at the site and their characteristics.
The geotechnical profile is composed of three geotechnical units: embankments (CW/CL — Geotechnical unit 1) and a base of highly erosive marls (HW — Geotechnical unit 2) as well as medium erosive marls (MW — Geotechnical unit 3).
The landslide remediation measures
As part of the landslide remediation, works are planned as part of increasing the global stability of the slope and the reconstruction of the road and the storm drainage system.
Landslide remediation is to be provided by the construction of a pile wall. The pile wall is to be made of reinforced concrete drilled piles with dimensions D = 620.0 mm / 540.0 mm, L = 6.0 m at a horizontal distance of 1.25 m. A retaining wall with a height of 2.50 m is to be installed on top of the piles, and its foundation is to act as the capping beam of the pilot wall. For the purpose of additional pile wall protection, it is planned to install rod anchors with a diameter of 32.0 mm and a length of 10.0 m at a horizontal distance of 2.50 m.
The site is currently undergoing road reconstruction, including the execution of a new culvert and an upgrade of the storm drainage system to mitigate future occurrences.
To assess the effectiveness of the designed interventions, a systematic observation plan is to be implemented during the execution of the construction works and subsequently during the exploitation phase. For this purpose, a vertical inclinometer with a length of 12.0 m is to be installed through the embankment to measure displacement accurately. Additionally, it is planned to conduct testing on all the piles to ensure their characteristics align with the design requirements.
