Landslide Remediation on the DC6 State Road, Jurovski Brod–Dvor Section
In Karlovac County, on the DC6 state road, in the Jurovski Brod–Dvor section, at station 14 + 400 km, two landslides have activated. The western landslide has occurred over a total width of approximately 65.0 m and affects the roadway over a width of about 40.0 m. The eastern landslide has occurred over a total width of approximately 55.0 m and affects the roadway over a width of about 30.0 m. Both landslides have been found downhill from the road.
The most likely cause of both landslides is inadequate drainage of the slope and road pavement, the load on the slope from traffic vibrations and the unfavorable inclination of the slope.
Geotechnical investigation and testing
For the landslide remediation design, we conducted engineering and geological as well as geotechnical investigation and testing. The works included:
- geological and geotechnical prospecting of the wider area;
- engineering and geological mapping of the terrain;
- exploratory drilling;
- a standard penetration test (SPT);
- inclinometer measurements;
- geophysical testing;
- laboratory testing; and
- an analysis of previous research.
As part of the exploratory drilling, six boreholes were drilled on the site, five with a depth of 8.0 meters and one with a depth of 13.0 meters. Inclinometer pipes were installed in two of the boreholes, and measurements of horizontal soil displacements were conducted to approximately determine the position of the slip surface at both landslides. Inclinometer testing revealed that the slip surface at both landslides occurs at approximately 3.50–4.0 m below the elevation of the existing road pavement.
In the investigated area, we also conducted geophysical seismic refraction tests on two (2) seismic profiles with a total length of 100.0 m.
By processing all the data, we prepared a geotechnical report that served as a basis for further landslide remediation design. The report provided insight into the shape and dimensions of the slip surface, as well as the materials at the site and their characteristics.
The geotechnical profile at the site consists of three (3) geotechnical units: made ground (GW — Geotechnical Unit 1), red clay (CL, CH — Geotechnical Unit 2), and highly to moderately weathered limestones (Geotechnical Unit 3).
Remediation measures for the eastern landslide
As part of the remediation of the eastern landslide, works are planned to enhance the overall stability of the slope over a length of 40.0 m (from station 13 + 830.50 to station 13 + 870.50). The remediation plan includes the construction of a pile wall using reinforced concrete bored piles with a length of 10.0 m and a nominal diameter of 620.0 mm / 540.0 mm, spaced 1.0 m apart. The piles are to be made of C-30/37-grade concrete. Above the piles, a reinforced concrete capping beam with dimensions measuring 62.0 cm × 60.0 cm (W × H) is to be constructed, also made of C-30/37-grade concrete.
In addition to these measures aimed at ensuring the overall stability of the slope, the reconstruction of the stormwater drainage system at the landslide location is also planned.
Remediation measures for the western landslide
As part of the remediation of the western landslide, construction works are planned to enhance the overall stability of the slope over a length of 40.0 m (from station 13 + 906.00 to station 13 + 946.00). Similarly to the eastern landslide, the remediation strategy involves the construction of a pile wall consisting of reinforced concrete bored piles with a length of 10.0 m and a nominal diameter of 620.0 mm / 540.0 mm, spaced 1.0 m apart.
Given that the planned reconstruction of this section of the state road includes a roadway widening into the slope, the design incorporates a reinforced concrete retaining wall with a height of 2.80 m above the piles. The foundation of this wall serves the dual purpose of interconnecting the piles (pile cap) and supporting the new roadway embankment. Additionally, the area behind the retaining wall is planned to be backfilled with stone material to stabilize the structure further. In conjunction with these stabilization measures, the reconstruction of the stormwater drainage system at the landslide location is also planned.
To verify the success of the designed interventions, a systematic monitoring process is planned during construction and, subsequently, during the execution phase. Additionally, all the piles that are to be constructed are also to be tested to ensure that their characteristics meet the project requirements.
A unique aspect of this landslide remediation design is that the remediation measures had to be coordinated with both the existing and the newly planned conditions of the roadway, as a reconstruction project for this section had already been prepared. The remediation works for both landslides will be carried out consecutively along with the reconstruction of the roadway for the entire section.
