Abstract (english) | A detailed analysis of the “Žirovac” landslide on Croatia’s state road section in the village of Žirovac is given in this case study. The landslide was triggered by the Petrinja earthquake in December 2020 and was subject to fast-paced processes of investigation and mitigation. The engineering geological and geotechnical survey including boreholes and geophysical investigations were performed on a large local scale. The earthquake-induced rotational landslide was observed on the road embankment section, which was reported to be an old landslide, continuously covered by new layers of gravel material. Despite the localized, earthquake-induced landslide, the wider slope area showed significant signs of terrain sliding and/or creeping which could be observed on the existing damaged buildings and shallow constructions. Performed investigation results indicated the presence of two landsliding mechanisms: (1) The local, rotational landslide of the road embankment induced by the Petrinja earthquake combined with the unfavorable load of the continuously added embankment layers and the underlying material degradation due to groundwater flow; (2) The global, translational creeping landslide of the wider slope area caused by occasional but significant groundwater flow and consequential degradation of the deeper-seated bedrock. The local landslide, as a primary subject of the investigation works performed, was limited to the road embankment section and embankment material. Although 225 m wide, the length of the local landslide was only 20 m, with a sliding surface depth of 2.5 m. The global landslide was reported as an old creeping landslide, causing occasional but continuous damage to the surrounding buildings and infrastructure. According to the investigation works performed, the global landslide was defined as a translational landslide, approximately 300 m wide and 300 m long with its sliding surface formed at a depth of 5-8 m, just above the underlying impermeable cretaceous clays. Although the investigated local landslide was induced by the Petrinja earthquake, the effect of the global landslide on the local sliding was taken into consideration in the engineering geological report for landslide mitigation purposes. The continuously reported local landslides, before the Petrinja earthquake, were probably induced by the continuous creep of the global landslide. This case study also observes the imperfections of the fast-paced, local-scale investigations for quick mitigation purposes regarding the landslide characteristics determination on a regional scale. |